Point Mutations In Proteins

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La caractérisation et l'identification d'une mutante de la pyruvate kinase

L’isoforme M2 du pyruvate kinase (PKM2) est responsable de la conversion du phosphoénolpyruvate (PEP) en pyruvate. Cette étape est la dernière étape de catalyse dans le processus de glycolyse puis joue un rôle essentiel dans la fermentation lactique effectuée chez les cellules anaérobiques, notamment les cellules myocardiques. De plus, le pyruvate kinase joue un rôle important dans le métabolisme des cellules cancéreuses. Au cours de cette expérience, nous caractérisent une mutante (K422R) de la PKM2 à l’aide de dosages enzymatiques des deux formes de l’enzyme en présence de certains effecteurs étant déjà identifiés comme régulateurs allostérique de la PKM2. La mutation a été confirmée à l’aide de séquençage et alignement de séquence avec la séquence protéique de la PKM2, retrouvée sur NCBI. Nos résultats démontrent que la mutation K422R favorise l’état T tétramérique et inactive de la PKM2 à cause de formation de liens stabilisantes au sein de la structure globulaire. La PKM2, sous sa forme active, existe plutôt sous l’état R tétramérique (3). Notre étude met en évidence une façon efficace de réguler l’activité enzymatique de la PKM2 à travers un changement dans la structure cristalline du type sauvage. Cette information s’avère utile pour des études dans le traitement du cancer qui vise à inhiber la fonction de la PKM2.

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- by Moriah Bertholet
- •
- 9
  Protein Stability, Pyruvate Kinase, Mutation, Allosteric Proteins

Molecular mechanism of Ras-related protein Rab-5A and effect of mutations in the catalytically active phosphate-binding loop

Ras-related protein (Rab-5a) is primarily involved in the regulation of early endosome fusion during endocytosis and takes part in the budding process. During GTP hydrolysis, Rab5a was spotted in the cytoplasmic side of early endo-somes in association with the GTP. Previous study suggested that the substitution of alanine with proline at position 30 of Rab5a reduces the GTPase activity around 12-fold, while, with arginine substitution stimulates the intrinsic GTP hydrolysis by 5-fold. Most of the other substitutions at this position show a little or no effect on the GTPase activity. In this paper, structure analysis and molecular dynamics (MD) simulation studies of human Rab5a and its mutants have been extensively carried out. The effect of binding of a non-hydrolyzable GTP analog guanosine-5′-(β, γ)-imidotriphos-phate (GppNHp) with Rab5a and its mutants are described. The objective of the current study is to perform a detailed examination of structural flexibility of Rab5a and its mutants p.Ala30Pro and p.Ala30Arg using MD simulations. Our observations suggest that mutant p.Ala30Arg stabilize the protein molecule when bound to GppNHp which offers additional contacts. Despite an in silico approach, this study provides a deep insight into the impact of mutation on the structure , function, stability, and mechanism of binding of GppNHp to the Rab5a at molecular level.

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Molecular Dynamics of Mesophilic-Like Mutants of a Cold-Adapted Enzyme: Insights into Distal Effects Induced by the Mutations

Networks and clusters of intramolecular interactions, as well as their ''communication'' across the three-dimensional architecture have a prominent role in determining protein stability and function. Special attention has been dedicated to their role in thermal adaptation. In the present contribution, seven previously experimentally characterized mutants of a cold-adapted a-amylase, featuring mesophilic-like behavior, have been investigated by multiple molecular dynamics simulations, essential dynamics and analyses of correlated motions and electrostatic interactions. Our data elucidate the molecular mechanisms underlying the ability of single and multiple mutations to globally modulate dynamic properties of the cold-adapted a-amylase, including both local and complex unpredictable distal effects. Our investigation also shows, in agreement with the experimental data, that the conversion of the cold-adapted enzyme in a warm-adapted variant cannot be completely achieved by the introduction of few mutations, also providing the rationale behind these effects. Moreover, pivotal residues, which are likely to mediate the effects induced by the mutations, have been identified from our analyses, as well as a group of suitable candidates for protein engineering. In fact, a subset of residues here identified (as an isoleucine, or networks of mesophilic-like salt bridges in the proximity of the catalytic site) should be considered, in experimental studies, to get a more efficient modification of the features of the cold-adapted enzyme.

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Molecular mechanism of Ras-related protein Rab-5A and effect of mutations in the catalytically active phosphate-binding loop

Ras-related protein (Rab-5a) is primarily involved in the regulation of early endosome fusion during endocytosis and takes part in the budding process. During GTP hydrolysis, Rab5a spotted in the cytoplasmic side of early endosomes in association with the GTP. Previous study suggested that substitution of alanine with proline at position 30 of Rab5a reduces the GTPase activity around 12-fold. While, with arginine substitution stimulates the intrinsic GTP hydrolysis by 5-fold. Most of the other substitutions at this position show a little or no effect on the GTPase activity. In this paper, structure analysis and molecular dynamics (MD) simulation studies of human Rab5a and its mutants have been extensively carried out. The effect of binding of a nonhydrolyzable GTP analog guanosine-5’-(β,γ)-imidotriphosphate (GppNHp) with Rab5a and its mutants are described. The objective of the current study is to perform a detailed examination of structural flexibility of Rab5a and its mutants p.Ala30Pro and p.Ala30Arg using MD simulations. Our observations suggest that mutant p.Ala30Arg stabilize the protein molecule when bound to GppNHp which offers additional contacts. Despite of an in silico approach, this
study provides a deep insight into the impact of mutation on the structure, function, stability and mechanism of binding of GppNHp to the Rab5a at molecular level.

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Stability scale and atomic solvation parameters extracted from 1023 mutation experiments

The stability scale of 20 amino acid residues is derived from a database of 1023 mutation experiments on 35 proteins. The resulting scale of hydrophobic residues has an excellent correlation with the octanol-to-water transfer free energy corrected with an additional Flory–Huggins molar-volume term (correlation coefficient r = 0.95, slope = 1.05, and a near zero intercept). Thus, hydrophobic contribution to folding stability is characterized remarkably well by transfer experiments. However, no corresponding correlation is found for hydrophilic residues. Both the hydrophilic portion and the entire scale, however, correlate strongly with average burial accessible surface (r = 0.76 and 0.97, respectively). Such a strong correlation leads to a near uniform value of the atomic solvation parameters for atoms C, S, O/N, O−0.5, and N+0.5,1. All are in the range of 12–28 cal mol−1 Å−2, close to the original estimate of hydrophobic contribution of 25–30 cal mol−1 Å−2 to folding stability. Without any adjustable parameters, the new stability scale and new atomic solvation parameters yielded an accurate prediction of protein–protein binding free energy for a separate database of 21 protein–protein complexes (r = 0.80 and slope = 1.06, and r = 0.83 and slope = 0.93, respectively). Proteins 2002;49:483–492. © 2002 Wiley-Liss, Inc.

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An Acidic Loop and Cognate Phosphorylation Sites Define a Molecular Switch That Modulates Ubiquitin Charging Activity in Cdc34-Like Enzymes

E2 ubiquitin-conjugating enzymes are crucial mediators of protein ubiquitination, which strongly influence the ultimate fate of the target substrates. Recently, it has been shown that the activity of several enzymes of the ubiquitination pathway is finely tuned by phosphorylation, an ubiquitous mechanism for cellular regulation, which modulates protein conformation. In this contribution, we provide the first rationale, at the molecular level, of the regulatory mechanism mediated by casein kinase 2 (CK2) phosphorylation of E2 Cdc34-like enzymes. In particular, we identify two co-evolving signature elements in one of the larger families of E2 enzymes: an acidic insertion in b4a2 loop in the proximity of the catalytic cysteine and two conserved key serine residues within the catalytic domain, which are phosphorylated by CK2. Our investigations, using yeast Cdc34 as a model, through 2.5 ms molecular dynamics simulations and biochemical assays, define these two elements as an important phosphorylation-controlled switch that modulate opening and closing of the catalytic cleft. The mechanism relies on electrostatic repulsions between a conserved serine phosphorylated by CK2 and the acidic residues of the b4a2 loop, promoting E2 ubiquitin charging activity. Our investigation identifies a new and unexpected pivotal role for the acidic loop, providing the first evidence that this loop is crucial not only for downstream events related to ubiquitin chain assembly, but is also mandatory for the modulation of an upstream crucial step of the ubiquitin pathway: the ubiquitin charging in the E2 catalytic cleft.

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- by Paola Coccetti and +1
  Valeria Ranzani
- •
- 16
  Thermodynamics, Molecular Dynamics Simulation, Principal Component Analysis, Protein Dynamics

Point Mutations In Proteins

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