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arXiv 1606.05802q-bio.PEq-bio.BM
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进化选择在蛋白质结构进化动力学中的作用

The role of evolutionary selection in the dynamics of protein structure evolution

Amy I. Gilson, Ahmee Marshall-Christensen, Jeong-Mo Choi, Eugene I. Shakhnovich

摘要:

新的蛋白质结构的出现已经被证明很难在自然界中追踪,也很难在实验室中进行工程改造。然而,结构进化的一个方面已被证明对从序列中确定蛋白质的三维结构非常有用:在绝大多数情况下,共享超过30%序列同一性的蛋白质具有相似的结构。在这个标记之下是“模糊区”,蛋白质可能具有相同或非常不同的结构。这些观察形成了结构同源建模背后的基本直觉。然而,尽管它们很重要,却从未得到过全面的生物物理理由。在这里,我们表明,发病的朦胧区是更渐进的蛋白质与低接触密度,一个代理低热力学稳定性,比蛋白质与高接触密度。然后,我们提出了一个分析模型,把分歧折叠进化作为一个激活的过程,在类比化学动力学,序列进化必须克服化学不稳定的进化中间体,发现新的折叠。这个模型解释了模糊区的存在,并解释了为什么某些蛋白质的出现比其他蛋白质更突然。我们测试模型的假设,并使用模型蛋白质和细胞群体的进化模拟来表征折叠进化的动力学。总的来说,这些结果显示了基本的生物物理约束如何指导演化动力学,从而导致现代蛋白质结构和序列的宇宙。

英文摘要:

Emergence of new protein structures has proved difficult to trace in nature and engineer in the laboratory. However, one aspect of structure evolution has proved immensely helpful for determining the three-dimensional structure of proteins from their sequences: in the vast majority of cases, proteins that share more than 30% sequence identity have similar structures. Below this mark is the "twilight zone" where proteins may have identical or very different structures. These observations form the foundational intuition behind structure homology modeling. Despite their importance, however, they have never received a comprehensive biophysical justification. Here we show that the onset of the twilight zone is more gradual for proteins with low contact density, a proxy for low thermodynamic stability, than proteins with high contact density. Then we present an analytical model that treats divergent fold evolution as an activated process, in analogy to chemical kinetics, where sequence evolution must overcome thermodynamically unstable evolutionary intermediates to discover new folds. This model explains the existence of a twilight zone and explains why its onset is more abrupt for some classes of proteins than for others. We test the assumptions of the model and characterize the dynamics of fold evolution using evolutionary simulations of model proteins and cell populations. Overall these results show how fundamental biophysical constraints directed evolutionary dynamics leading to the Universe of modern protein structures and sequences.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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