A lover of the outdoors, music and cycling who is obsessed with the role of protein modifications in the language of cells. Also an ardent believer in the need for political reform and an education system that works for everyone.
Phosphorylation of proteins on tyrosine (Tyr) residues evolved in metazoan organisms as a mechani... more Phosphorylation of proteins on tyrosine (Tyr) residues evolved in metazoan organisms as a mechanism of coordinating tissue growth1. Multicellular eukaryotes typically have more than 50 distinct protein Tyr kinases that catalyse the phosphorylation of thousands of Tyr residues throughout the proteome1–3. How a given Tyr kinase can phosphorylate a specific subset of proteins at unique Tyr sites is only partially understood4–7. Here we used combinatorial peptide arrays to profile the substrate sequence specificity of all human Tyr kinases. Globally, the Tyr kinases demonstrate considerable diversity in optimal patterns of residues surrounding the site of phosphorylation, revealing the functional organization of the human Tyr kinome by substrate motif preference. Using this information, Tyr kinases that are most compatible with phosphorylating any Tyr site can be identified. Analysis of mass spectrometry phosphoproteomic datasets using this compendium of kinase specificities accurately identifies specific Tyr kinases that are dysregulated in cells after stimulation with growth factors, treatment with anti-cancer drugs or expression of oncogenic variants. Furthermore, the topology of known Tyr signalling networks naturally emerged from a comparison of the sequence specificities of the Tyr kinases and the SH2 phosphotyrosine (pTyr)-binding domains. Finally we show that the intrinsic substrate specificity of Tyr kinases has remained fundamentally unchanged from worms to humans, suggesting that the fidelity between Tyr kinases and their protein substrate sequences has been maintained across hundreds of millions of years of evolution.
The clonal selection theory of the immune response elegantly solves the problem of how it is poss... more The clonal selection theory of the immune response elegantly solves the problem of how it is possible for an individual to make antibodies to virtually any foreign antigen. It does this by postulating that each lymphocyte can only produce antibodies of a single specificity and that a very large number of distinct lymphocytes exist. That may be restated to say that the universe of foreign antigens is matched by an internal universe of lymphocytes. The penalty exacted by this strategy for achieving antibody diversity is that lymphocytes specific for any particular antigenic determinant exist at very low frequency in an unimmunized animal. Since immune responses must be both prompt and of considerable magnitude if they are to protect against pathogenic microorganisms or against newly emerging tumor cells, it is clear that the rare cells specific for any particular antigen must expand in number rapidly. Thus, growth regulation of lymphocytes is a matter of central importance in the physiology of the immune system.
Double immunodiffusion owes its success to the unique nature of antibody‐antigen interactions. Wh... more Double immunodiffusion owes its success to the unique nature of antibody‐antigen interactions. When polyvalent antibodies with moderate‐to‐high intrinsic affinities are mixed with antigen at the right ratio (called the zone of equivalence) lattices of antibody‐antigen complexes form and precipitate out of solution. When, as described in this unit, gradients of antigen and antibody are established by diffusion from adjacent wells in a bed of agar, a line of practically insoluble precipitation forms at the equivalence zone (precipitin lines).
Most tools developed to visualize hierarchically clustered heatmaps generate static images. Clust... more Most tools developed to visualize hierarchically clustered heatmaps generate static images. Clustergrammer is a web-based visualization tool with interactive features such as: zooming, panning, filtering, reordering, sharing, performing enrichment analysis, and providing dynamic gene annotations. Clustergrammer can be used to generate shareable interactive visualizations by uploading a data table to a web-site, or by embedding Clustergrammer in Jupyter Notebooks. The Clustergrammer core libraries can also be used as a toolkit by developers to generate visualizations within their own applications. Clustergrammer is demonstrated using gene expression data from the cancer cell line encyclopedia (CCLE), original post-translational modification data collected from lung cancer cells lines by a mass spectrometry approach, and original cytometry by time of flight (CyTOF) single-cell proteomics data from blood. Clustergrammer enables producing interactive web based visualizations for the analysis of diverse biological data.
Here, we report the identification and characterization of a novel tyrosine phosphorylation site ... more Here, we report the identification and characterization of a novel tyrosine phosphorylation site in the carboxy-terminal Src Homology 3 (SH3) (SH3C) domain of the Crk adaptor protein. Y251 is located in the highly conserved RT loop structure of the SH3C, a region of Crk involved in the allosteric regulation of the Abl kinase. Exploiting kinase assays to show that Y251 is phosphorylated by Abl in vitro, we generated affinity-purified antisera against phosphorylated Y251 in Crk and showed that Abl induces phosphorylation at Y251 in vivo, and that the kinetics of phosphorylation at Y251 and the negative regulatory Y221 site in vitro are similar. Y251 on endogenous Crk was robustly phosphorylated in chronic myelogenous leukemia cell lines and in A431 and MDA-MB-468 cells stimulated with epidermal growth factor. Using streptavidin-biotin pull downs and unbiased high-throughput Src Homology 2 (SH2) profiling approaches, we found that a pY251 phosphopeptide binds specifically to a subset of SH2 domains, including Abl and Arg SH2, and that binding of pY251 to Abl SH2 induces transactivation of Abl 1b. Finally, the Y251F Crk mutant significantly abrogates Abl transactivation in vitro and in vivo. These studies point to a yet unrealized positive regulatory role resulting from tyrosine phosphorylation of Crk, and identify a novel mechanism by which an adaptor protein activates a non-receptor tyrosine kinase by SH2 domain displacement.
For 15 years the mission of PhosphoSitePlus ® (PSP, https://www.phosphosite.org) has been to prov... more For 15 years the mission of PhosphoSitePlus ® (PSP, https://www.phosphosite.org) has been to provide comprehensive information and tools for the study of mammalian post-translational modifications (PTMs). The number of unique PTMs in PSP is now more than 450 000 from over 22 000 articles and thousands of MS datasets. The most important areas of growth in PSP are in disease and isoform informatics. Germline mutations associated with inherited diseases and somatic cancer mutations have been added to the database and can now be viewed along with PTMs and associated quantitative information on novel 'lollipop' plots. These plots enable researchers to interactively visualize the overlap between disease variants and PTMs, and to identify mutations that may alter phenotypes by rewiring signaling networks. We are expanding the sequence space to include over 30 000 human and mouse isoforms to enable researchers to explore the important but understudied biology of isoforms. This represents a necessary expansion of sequence space to accommodate the growing precision and depth of coverage enabled by ongoing advances in mass spectrometry. Isoforms are aligned using a new algorithm. Exploring the worlds of PTMs and disease mutations in the entire isoform space will hopefully lead to new biomarkers, therapeutic targets, and insights into isoform biology.
Cross-linkage of membrane receptors of B cells leads to cellular activation and progress through ... more Cross-linkage of membrane receptors of B cells leads to cellular activation and progress through the G1 phase of the cell cycle. Entry into S phase is generally determined by the action of costimulatory factors. We describe here the cellular biochemical events which result in B cell activation as a result of cross-linkage of membrane receptors and present evidence for a feedback regulatory mechanism which leads to cellular desensitization. We further describe the purification, characterization, and receptor-binding properties of B cell stimulatory factor-1 (BSF-1), a T cell-derived lymphokine whose action is important in B cell entry into S phase. We provide evidence that BSF-1 acts as a cocompetence factor in the growth regulation of B and T lymphocytes and suggest that it acts in a similar manner on all cells of hematopoietic lineage.
Many scientists use quantitative measurements to compare the presence and amount, of various prot... more Many scientists use quantitative measurements to compare the presence and amount, of various proteins and nucleotides among series of one- and two-dimensional (1-D and 2-D) electrophoretic gels. These gels are often scanned into digital image files. Gel spots are then quantified using stand-alone analysis software. However, as more research collaborations take place over the Internet, it has become useful to share intermediate quantitative data between researchers. This allows research group members to investigate their data and share their work in progress. We developed a World Wide Web group-accessible software system, WebGel, for interactively exploring qualitative and quantitative differences between electrophoretic gels. Such Internet databases are useful for publishing quantitative data and allow other researchers to explore the data with respect to their own research. Because intermediate results of one user may be shared with their collaborators using WebGel, this form of active data-sharing constitutes a groupware method for enhancing collaborative research. Quantitative and image gel data from a stand-alone gel image processing system are copied to a database accessible on the WebGel Web server. These data are then available for analysis by the WebGel database program residing on that server. Visualization is critical for better understanding of the data. WebGel helps organize labeled gel images into montages of corresponding spots as seen in these different gels. Various views of multiple gel images, including sets of spots, normalization spots, labeled spots, segmented gels, etc. may also be displayed. These displays are active and may be used for performing database operations directly on individual protein spots by simply clicking on them. Corresponding regions between sets of gels may be visually analyzed using Flicker-comparison (Electrophoresis 1997, 18, 122-140) as one of the WebGel methods for qualitative analysis. Quantitative exploratory data analysis can be performed by comparing protein concentration values between corresponding spots for multiple samples run in separate gels. These data are then used to generate reports on statistical differences between sets of gels (e.g., between different disease states such as benign or metastatic cancers, etc.). Using combined visual and quantitative methods, WebGel can help bridge the analysis of dissimilar gels which are difficult to analyze with stand-alone systems and can serve as a collaborative Internet tool in a groupware setting.
Proceedings of the National Academy of Sciences of the United States of America, Apr 1, 1988
Lamin B is rapidly phosphorylated in lymphocytes after activation of protein kinase C (signal tra... more Lamin B is rapidly phosphorylated in lymphocytes after activation of protein kinase C (signal transduction/nuclear lamina/protein kinase M/two-dimensional chromatography)
Lymphocyte growth and differentiation are controlled by signals resulting from the interaction of... more Lymphocyte growth and differentiation are controlled by signals resulting from the interaction of antigen and cellular products, such as lymphokines, with specific cell membrane receptors. Resting B lymphocytes can be activated by low concentrations (l-5 &ml) of antibodies to membrane IgM, which is the B-lymphocyte receptor for antigen. The binding of anti-IgM to B cells causes a rapid increase in intracellular free calcium concentration ([Ca"]i), in inositol phosphate concentration, and in protein kinase activity. Moreover, the effects of anti-IgM on B cells are mimicked by the combined use of calcium ionophores and phorbol esters. Since phorbol esters activate protein kinase c, this suggests that the increase in [Ca*']i and in phosphatidylinositol metabolism stimulated by anti-&M are critical events in B-cell activation. The entry into S phase of B cells stimulated with anti-IgM depends on the action of a T-cell-derived factor designated B-cell stimulatory factor (BSF)-1. This is a 20,000-Da protein which is a powerful inducer of class II major histocompatibility complex molecules. Although an important cofactor for B-cell proliferative responses to anti-IgM, its major locus of action is on resting B cells. B cells stimulated with anti-IgM and BSF-1 do not synthesize secretory IgM. However, if two additional T-cellderived factors, B 15 I-TRF and interleukin-2, are added to cultures, a substantial proportion of stimulated B cells produce secretory IgM. BSF-1 has also been shown to participate in the "switch" in Ig class expression. Resting B cells cultured with lipopolysaccharide will switch to IgG, secretion in the presence of purified BSF-1.
Proceedings of the National Academy of Sciences of the United States of America, Aug 1, 1988
Thy-1, a cell-surface glycoprotein of undetermined function, is expressed in relatively large amo... more Thy-1, a cell-surface glycoprotein of undetermined function, is expressed in relatively large amounts on mouse thymocytes, peripheral T cells, and neurons. It is widely used as a marker to distinguish peripheral T cells from B cells in mice. We show here that, in five distinct mouse strains, recombinant interleukin 4 (IL-4/B-cell stimulatory factor 1) strikingly induces membrane expression of Thy-i on the vast majority of lipopolysaccharide (LPS)-stimulated normal murine B cells. Thy-1 + B cells are precursors for immunoglobulinsecreting cells. RNA blot analysis indicates that B cells express a Thy-i mRNA of 1.8 kilobases, the same size as that found in T cells. Cell mixing experiments show that only cells derived from Thy-1.2' donors express Thy-1.2, indicating that B cells expressing Thy-1 have not passively absorbed the glycoprotein from another cell source. Recombinant interferon-y inhibits Thy-1 induction by B cells stimulated with LPS and IL-4. Thy-1 is also induced on B cells that have been stimulated as a result of the specific activation of an IL-4-producing T-helper clone. Anti-IL-4 monoclonal antibody inhibits the induction of B-cell Thy-1 in this T-cell-B-cell interaction.
Current protocols in molecular biology, Jul 1, 1991
This unit describes six different ELISA systems for the detection of specific antibodies, soluble... more This unit describes six different ELISA systems for the detection of specific antibodies, soluble antigens, or cell-surface antigens. In all six systems, soluble reactants are removed from solution after specifically binding to solid-phase reactants. In the first four protocols, solid-phase reactants are prepared by adsorbing an antigen or antibody onto plastic microtiter plates; in the next two protocols, the solid-phase reactants are cell-associated molecules. In all protocols, the solid-phase reagents are incubated with secondary or tertiary reactants covalently coupled to an enzyme. Unbound conjugates are washed out and a chromogenic or fluorogenic substrate is added. As the substrate is hydrolyzed by the bound enzyme conjugate, a colored or fluorescent product is generated. Finally, the product is detected visually or with a microtiter plate reader. The amount of product generated is proportional to the amount of analysate in the test mixture. Support protocols are provided for optimizing the different ELISAs and preparing lysates for use as test antigen from bacterial cultures containing expressed protein.
Differences in the binding of the substrate analogue chitotriose to lysozymes correlate with amin... more Differences in the binding of the substrate analogue chitotriose to lysozymes correlate with amino acid substitutions in the binding site and not with substitutions elsewhere. This is evident from binding studies done with an immunological method as well as a conventional spectroscopic method. The immunological technique, based on the microcomplement fixation assay, required thousands of times less lysozyme than did the conventional technique. For eight bird lysozymes of known amino acid sequence, the immunologically and physically measured association constants were in approximate agreement. Five of the eight lysozymes have about the same affinity for chitotriose and have identical amino acids at the sites of contact between substrate and enzyme. In contrast, the three lysozymes that have altered affinities have amino acid substitutions in the binding site. Some of the lysozymes with similar affinities for chitotriose differ greatly in amino acid sequence outside the binding site. This suggests that evolutionary substitutions do not generally have long-range effects on the active site region of lysozyme.
Phosphorylation of proteins on tyrosine (Tyr) residues evolved in metazoan organisms as a mechani... more Phosphorylation of proteins on tyrosine (Tyr) residues evolved in metazoan organisms as a mechanism of coordinating tissue growth1. Multicellular eukaryotes typically have more than 50 distinct protein Tyr kinases that catalyse the phosphorylation of thousands of Tyr residues throughout the proteome1–3. How a given Tyr kinase can phosphorylate a specific subset of proteins at unique Tyr sites is only partially understood4–7. Here we used combinatorial peptide arrays to profile the substrate sequence specificity of all human Tyr kinases. Globally, the Tyr kinases demonstrate considerable diversity in optimal patterns of residues surrounding the site of phosphorylation, revealing the functional organization of the human Tyr kinome by substrate motif preference. Using this information, Tyr kinases that are most compatible with phosphorylating any Tyr site can be identified. Analysis of mass spectrometry phosphoproteomic datasets using this compendium of kinase specificities accurately identifies specific Tyr kinases that are dysregulated in cells after stimulation with growth factors, treatment with anti-cancer drugs or expression of oncogenic variants. Furthermore, the topology of known Tyr signalling networks naturally emerged from a comparison of the sequence specificities of the Tyr kinases and the SH2 phosphotyrosine (pTyr)-binding domains. Finally we show that the intrinsic substrate specificity of Tyr kinases has remained fundamentally unchanged from worms to humans, suggesting that the fidelity between Tyr kinases and their protein substrate sequences has been maintained across hundreds of millions of years of evolution.
The clonal selection theory of the immune response elegantly solves the problem of how it is poss... more The clonal selection theory of the immune response elegantly solves the problem of how it is possible for an individual to make antibodies to virtually any foreign antigen. It does this by postulating that each lymphocyte can only produce antibodies of a single specificity and that a very large number of distinct lymphocytes exist. That may be restated to say that the universe of foreign antigens is matched by an internal universe of lymphocytes. The penalty exacted by this strategy for achieving antibody diversity is that lymphocytes specific for any particular antigenic determinant exist at very low frequency in an unimmunized animal. Since immune responses must be both prompt and of considerable magnitude if they are to protect against pathogenic microorganisms or against newly emerging tumor cells, it is clear that the rare cells specific for any particular antigen must expand in number rapidly. Thus, growth regulation of lymphocytes is a matter of central importance in the physiology of the immune system.
Double immunodiffusion owes its success to the unique nature of antibody‐antigen interactions. Wh... more Double immunodiffusion owes its success to the unique nature of antibody‐antigen interactions. When polyvalent antibodies with moderate‐to‐high intrinsic affinities are mixed with antigen at the right ratio (called the zone of equivalence) lattices of antibody‐antigen complexes form and precipitate out of solution. When, as described in this unit, gradients of antigen and antibody are established by diffusion from adjacent wells in a bed of agar, a line of practically insoluble precipitation forms at the equivalence zone (precipitin lines).
Most tools developed to visualize hierarchically clustered heatmaps generate static images. Clust... more Most tools developed to visualize hierarchically clustered heatmaps generate static images. Clustergrammer is a web-based visualization tool with interactive features such as: zooming, panning, filtering, reordering, sharing, performing enrichment analysis, and providing dynamic gene annotations. Clustergrammer can be used to generate shareable interactive visualizations by uploading a data table to a web-site, or by embedding Clustergrammer in Jupyter Notebooks. The Clustergrammer core libraries can also be used as a toolkit by developers to generate visualizations within their own applications. Clustergrammer is demonstrated using gene expression data from the cancer cell line encyclopedia (CCLE), original post-translational modification data collected from lung cancer cells lines by a mass spectrometry approach, and original cytometry by time of flight (CyTOF) single-cell proteomics data from blood. Clustergrammer enables producing interactive web based visualizations for the analysis of diverse biological data.
Here, we report the identification and characterization of a novel tyrosine phosphorylation site ... more Here, we report the identification and characterization of a novel tyrosine phosphorylation site in the carboxy-terminal Src Homology 3 (SH3) (SH3C) domain of the Crk adaptor protein. Y251 is located in the highly conserved RT loop structure of the SH3C, a region of Crk involved in the allosteric regulation of the Abl kinase. Exploiting kinase assays to show that Y251 is phosphorylated by Abl in vitro, we generated affinity-purified antisera against phosphorylated Y251 in Crk and showed that Abl induces phosphorylation at Y251 in vivo, and that the kinetics of phosphorylation at Y251 and the negative regulatory Y221 site in vitro are similar. Y251 on endogenous Crk was robustly phosphorylated in chronic myelogenous leukemia cell lines and in A431 and MDA-MB-468 cells stimulated with epidermal growth factor. Using streptavidin-biotin pull downs and unbiased high-throughput Src Homology 2 (SH2) profiling approaches, we found that a pY251 phosphopeptide binds specifically to a subset of SH2 domains, including Abl and Arg SH2, and that binding of pY251 to Abl SH2 induces transactivation of Abl 1b. Finally, the Y251F Crk mutant significantly abrogates Abl transactivation in vitro and in vivo. These studies point to a yet unrealized positive regulatory role resulting from tyrosine phosphorylation of Crk, and identify a novel mechanism by which an adaptor protein activates a non-receptor tyrosine kinase by SH2 domain displacement.
For 15 years the mission of PhosphoSitePlus ® (PSP, https://www.phosphosite.org) has been to prov... more For 15 years the mission of PhosphoSitePlus ® (PSP, https://www.phosphosite.org) has been to provide comprehensive information and tools for the study of mammalian post-translational modifications (PTMs). The number of unique PTMs in PSP is now more than 450 000 from over 22 000 articles and thousands of MS datasets. The most important areas of growth in PSP are in disease and isoform informatics. Germline mutations associated with inherited diseases and somatic cancer mutations have been added to the database and can now be viewed along with PTMs and associated quantitative information on novel 'lollipop' plots. These plots enable researchers to interactively visualize the overlap between disease variants and PTMs, and to identify mutations that may alter phenotypes by rewiring signaling networks. We are expanding the sequence space to include over 30 000 human and mouse isoforms to enable researchers to explore the important but understudied biology of isoforms. This represents a necessary expansion of sequence space to accommodate the growing precision and depth of coverage enabled by ongoing advances in mass spectrometry. Isoforms are aligned using a new algorithm. Exploring the worlds of PTMs and disease mutations in the entire isoform space will hopefully lead to new biomarkers, therapeutic targets, and insights into isoform biology.
Cross-linkage of membrane receptors of B cells leads to cellular activation and progress through ... more Cross-linkage of membrane receptors of B cells leads to cellular activation and progress through the G1 phase of the cell cycle. Entry into S phase is generally determined by the action of costimulatory factors. We describe here the cellular biochemical events which result in B cell activation as a result of cross-linkage of membrane receptors and present evidence for a feedback regulatory mechanism which leads to cellular desensitization. We further describe the purification, characterization, and receptor-binding properties of B cell stimulatory factor-1 (BSF-1), a T cell-derived lymphokine whose action is important in B cell entry into S phase. We provide evidence that BSF-1 acts as a cocompetence factor in the growth regulation of B and T lymphocytes and suggest that it acts in a similar manner on all cells of hematopoietic lineage.
Many scientists use quantitative measurements to compare the presence and amount, of various prot... more Many scientists use quantitative measurements to compare the presence and amount, of various proteins and nucleotides among series of one- and two-dimensional (1-D and 2-D) electrophoretic gels. These gels are often scanned into digital image files. Gel spots are then quantified using stand-alone analysis software. However, as more research collaborations take place over the Internet, it has become useful to share intermediate quantitative data between researchers. This allows research group members to investigate their data and share their work in progress. We developed a World Wide Web group-accessible software system, WebGel, for interactively exploring qualitative and quantitative differences between electrophoretic gels. Such Internet databases are useful for publishing quantitative data and allow other researchers to explore the data with respect to their own research. Because intermediate results of one user may be shared with their collaborators using WebGel, this form of active data-sharing constitutes a groupware method for enhancing collaborative research. Quantitative and image gel data from a stand-alone gel image processing system are copied to a database accessible on the WebGel Web server. These data are then available for analysis by the WebGel database program residing on that server. Visualization is critical for better understanding of the data. WebGel helps organize labeled gel images into montages of corresponding spots as seen in these different gels. Various views of multiple gel images, including sets of spots, normalization spots, labeled spots, segmented gels, etc. may also be displayed. These displays are active and may be used for performing database operations directly on individual protein spots by simply clicking on them. Corresponding regions between sets of gels may be visually analyzed using Flicker-comparison (Electrophoresis 1997, 18, 122-140) as one of the WebGel methods for qualitative analysis. Quantitative exploratory data analysis can be performed by comparing protein concentration values between corresponding spots for multiple samples run in separate gels. These data are then used to generate reports on statistical differences between sets of gels (e.g., between different disease states such as benign or metastatic cancers, etc.). Using combined visual and quantitative methods, WebGel can help bridge the analysis of dissimilar gels which are difficult to analyze with stand-alone systems and can serve as a collaborative Internet tool in a groupware setting.
Proceedings of the National Academy of Sciences of the United States of America, Apr 1, 1988
Lamin B is rapidly phosphorylated in lymphocytes after activation of protein kinase C (signal tra... more Lamin B is rapidly phosphorylated in lymphocytes after activation of protein kinase C (signal transduction/nuclear lamina/protein kinase M/two-dimensional chromatography)
Lymphocyte growth and differentiation are controlled by signals resulting from the interaction of... more Lymphocyte growth and differentiation are controlled by signals resulting from the interaction of antigen and cellular products, such as lymphokines, with specific cell membrane receptors. Resting B lymphocytes can be activated by low concentrations (l-5 &ml) of antibodies to membrane IgM, which is the B-lymphocyte receptor for antigen. The binding of anti-IgM to B cells causes a rapid increase in intracellular free calcium concentration ([Ca"]i), in inositol phosphate concentration, and in protein kinase activity. Moreover, the effects of anti-IgM on B cells are mimicked by the combined use of calcium ionophores and phorbol esters. Since phorbol esters activate protein kinase c, this suggests that the increase in [Ca*']i and in phosphatidylinositol metabolism stimulated by anti-&M are critical events in B-cell activation. The entry into S phase of B cells stimulated with anti-IgM depends on the action of a T-cell-derived factor designated B-cell stimulatory factor (BSF)-1. This is a 20,000-Da protein which is a powerful inducer of class II major histocompatibility complex molecules. Although an important cofactor for B-cell proliferative responses to anti-IgM, its major locus of action is on resting B cells. B cells stimulated with anti-IgM and BSF-1 do not synthesize secretory IgM. However, if two additional T-cellderived factors, B 15 I-TRF and interleukin-2, are added to cultures, a substantial proportion of stimulated B cells produce secretory IgM. BSF-1 has also been shown to participate in the "switch" in Ig class expression. Resting B cells cultured with lipopolysaccharide will switch to IgG, secretion in the presence of purified BSF-1.
Proceedings of the National Academy of Sciences of the United States of America, Aug 1, 1988
Thy-1, a cell-surface glycoprotein of undetermined function, is expressed in relatively large amo... more Thy-1, a cell-surface glycoprotein of undetermined function, is expressed in relatively large amounts on mouse thymocytes, peripheral T cells, and neurons. It is widely used as a marker to distinguish peripheral T cells from B cells in mice. We show here that, in five distinct mouse strains, recombinant interleukin 4 (IL-4/B-cell stimulatory factor 1) strikingly induces membrane expression of Thy-i on the vast majority of lipopolysaccharide (LPS)-stimulated normal murine B cells. Thy-1 + B cells are precursors for immunoglobulinsecreting cells. RNA blot analysis indicates that B cells express a Thy-i mRNA of 1.8 kilobases, the same size as that found in T cells. Cell mixing experiments show that only cells derived from Thy-1.2' donors express Thy-1.2, indicating that B cells expressing Thy-1 have not passively absorbed the glycoprotein from another cell source. Recombinant interferon-y inhibits Thy-1 induction by B cells stimulated with LPS and IL-4. Thy-1 is also induced on B cells that have been stimulated as a result of the specific activation of an IL-4-producing T-helper clone. Anti-IL-4 monoclonal antibody inhibits the induction of B-cell Thy-1 in this T-cell-B-cell interaction.
Current protocols in molecular biology, Jul 1, 1991
This unit describes six different ELISA systems for the detection of specific antibodies, soluble... more This unit describes six different ELISA systems for the detection of specific antibodies, soluble antigens, or cell-surface antigens. In all six systems, soluble reactants are removed from solution after specifically binding to solid-phase reactants. In the first four protocols, solid-phase reactants are prepared by adsorbing an antigen or antibody onto plastic microtiter plates; in the next two protocols, the solid-phase reactants are cell-associated molecules. In all protocols, the solid-phase reagents are incubated with secondary or tertiary reactants covalently coupled to an enzyme. Unbound conjugates are washed out and a chromogenic or fluorogenic substrate is added. As the substrate is hydrolyzed by the bound enzyme conjugate, a colored or fluorescent product is generated. Finally, the product is detected visually or with a microtiter plate reader. The amount of product generated is proportional to the amount of analysate in the test mixture. Support protocols are provided for optimizing the different ELISAs and preparing lysates for use as test antigen from bacterial cultures containing expressed protein.
Differences in the binding of the substrate analogue chitotriose to lysozymes correlate with amin... more Differences in the binding of the substrate analogue chitotriose to lysozymes correlate with amino acid substitutions in the binding site and not with substitutions elsewhere. This is evident from binding studies done with an immunological method as well as a conventional spectroscopic method. The immunological technique, based on the microcomplement fixation assay, required thousands of times less lysozyme than did the conventional technique. For eight bird lysozymes of known amino acid sequence, the immunologically and physically measured association constants were in approximate agreement. Five of the eight lysozymes have about the same affinity for chitotriose and have identical amino acids at the sites of contact between substrate and enzyme. In contrast, the three lysozymes that have altered affinities have amino acid substitutions in the binding site. Some of the lysozymes with similar affinities for chitotriose differ greatly in amino acid sequence outside the binding site. This suggests that evolutionary substitutions do not generally have long-range effects on the active site region of lysozyme.
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Papers by Peter Hornbeck
is only partially understood4–7. Here we used combinatorial peptide arrays to profile the substrate sequence specificity of all human Tyr kinases. Globally, the Tyr kinases demonstrate considerable diversity in optimal patterns of residues surrounding
the site of phosphorylation, revealing the functional organization of the human Tyr kinome by substrate motif preference. Using this information, Tyr kinases that are most compatible with phosphorylating any Tyr site can be identified. Analysis of
mass spectrometry phosphoproteomic datasets using this compendium of kinase specificities accurately identifies specific Tyr kinases that are dysregulated in cells after stimulation with growth factors, treatment with anti-cancer drugs or expression of oncogenic variants. Furthermore, the topology of known Tyr signalling networks naturally emerged from a comparison of the sequence specificities of the Tyr kinases and the SH2 phosphotyrosine (pTyr)-binding domains. Finally we show that the intrinsic substrate specificity of Tyr kinases has remained fundamentally unchanged from worms to humans, suggesting that the fidelity between Tyr kinases and their protein substrate sequences has been maintained across hundreds of millions of years of evolution.
is only partially understood4–7. Here we used combinatorial peptide arrays to profile the substrate sequence specificity of all human Tyr kinases. Globally, the Tyr kinases demonstrate considerable diversity in optimal patterns of residues surrounding
the site of phosphorylation, revealing the functional organization of the human Tyr kinome by substrate motif preference. Using this information, Tyr kinases that are most compatible with phosphorylating any Tyr site can be identified. Analysis of
mass spectrometry phosphoproteomic datasets using this compendium of kinase specificities accurately identifies specific Tyr kinases that are dysregulated in cells after stimulation with growth factors, treatment with anti-cancer drugs or expression of oncogenic variants. Furthermore, the topology of known Tyr signalling networks naturally emerged from a comparison of the sequence specificities of the Tyr kinases and the SH2 phosphotyrosine (pTyr)-binding domains. Finally we show that the intrinsic substrate specificity of Tyr kinases has remained fundamentally unchanged from worms to humans, suggesting that the fidelity between Tyr kinases and their protein substrate sequences has been maintained across hundreds of millions of years of evolution.