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arXiv 1308.4342q-bio.PEq-bio.BM
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考虑结构约束的蛋白质进化模型的新表述

A new formulation of protein evolutionary models that account for structural constraints

Andrew J. Bordner, Hans D. Mittelmann

摘要:

尽管具有保守折叠的结构稳定性对蛋白质功能的重要性,但几乎所有的进化模型都忽略了由相邻氨基酸位点之间的物理相互作用引起的位点-位点相关性。这主要是由于难以制定一个计算上易于处理的模型,因为率矩阵可以不再使用。在这里,我们介绍了一个通用的框架,因子图的基础上,构建概率模型的蛋白质进化与网站的相互依赖性。方便地,有效的近似推理算法,如置信传播,可以用来计算这些模型的似然性。我们适合这种类型的氨基酸取代模型,占溶剂的可及性和网站的相关性。新模型与速率矩阵模型和仅考虑溶剂可及性的模型的比较表明,它更好地拟合序列数据。我们还研究了同六聚体酶家族内的进化,发现大多数接触亚基之间的位点相关性有助于更高的可能性。此外,我们表明,新的替代模型有一个类似的数学形式(Rodrigue等人,2005年)中介绍的,虽然不同的参数解释和值。我们还进行了统计分析的氨基酸在相邻的网站上的替代概率的影响,并找到一个显着的扰动的概率,进一步支持蛋白质进化中的重要作用的站点站点之间的相互作用,并激励新的进化模型的发展,如这里所描述的。最后,我们讨论了新的替代模型的可能的扩展和应用。

英文摘要:

Despite the importance of a thermodynamically stable structure with a conserved fold for protein function, almost all evolutionary models neglect site-site correlations that arise from physical interactions between neighboring amino acid sites. This is mainly due to the difficulty in formulating a computationally tractable model since rate matrices can no longer be used. Here we introduce a general framework, based on factor graphs, for constructing probabilistic models of protein evolution with site interdependence. Conveniently, efficient approximate inference algorithms, like Belief Propagation, can be used to calculate likelihoods for these models. We fit an amino acid substitution model of this type that accounts for both solvent accessibility and site-site correlations. Comparisons of the new model with rate matrix models and a model accounting only for solvent accessibility demonstrate that it better fits the sequence data. We also examine evolution within a family of homohexameric enzymes and find that site-site correlations between most contacting subunits contribute to a higher likelihood. In addition, we show that the new substitution model has a similar mathematical form to the one introduced in (Rodrigue et al. 2005), although with different parameter interpretations and values. We also perform a statistical analysis of the effects of amino acids at neighboring sites on substitution probabilities and find a significant perturbation of most probabilities, further supporting the significant role of site-site interactions in protein evolution and motivating the development of new evolutionary models like the one described here. Finally, we discuss possible extensions and applications of the new substitution models.

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