3-10序列空间上的随机事件--它们在蛋白质宇宙中偶然发生的原因及其意义
3-10 and Pi-Helices: Stochastic Events on Sequence Space; Reasons and Implications of their Accidental Occurrences across Protein Universe
摘要：
考虑到所有可用的非冗余蛋白质结构在不同的结构类别，本研究确定的概率特性，描述了几个方面的出现3（10）和π螺旋的蛋白质。3（10）和Pi螺旋的出现情况表明，它们的存在遵循一级结构上的泊松流;这意味着，它们的出现情况是罕见的，随机的和偶然的。3（10）和Pi-螺旋连续出现之间的序列间隔的结构类特异性统计分析表明，这些可以最好地描述伽马和指数分布，跨结构类。3（10）、Pi和α-螺旋中非甘氨酸和非脯氨酸残基的归一化百分比的比较研究揭示了在Ramachandran图谱的不允许、慷慨和允许区域中3（10）和Pi-螺旋残基的相当高的比例。从进化的角度对这些发现进行探讨，清楚地表明3（10）螺旋和π-螺旋应被适当地看作是长时间尺度上的进化中间体，因为不仅α-螺旋构象，而且“转角”的可能性也是相等的。因此，3（10）和π-螺旋的偶然和随机性质，以及它们的进化非保守性，可以从一个不变的定量框架来描述和解释。本文还研究了以前提出的关于3（10）螺旋和π螺旋的两个假设的正确程度。除此之外，提出了一种新的算法来区分相关序列，该算法可靠地研究了蛋白质二级结构的进化距离。
英文摘要：
Considering all available non-redundant protein structures across different structural classes, present study identified the probabilistic characteristics that describe several facets of the occurrence of 3(10) and Pi-helices in proteins. Occurrence profile of 3(10) and Pi-helices revealed that, their presence follows Poisson flow on the primary structure; implying that, their occurrence profile is rare, random and accidental. Structural class-specific statistical analyses of sequence intervals between consecutive occurrences of 3(10) and Pi-helices revealed that these could be best described by gamma and exponential distributions, across structural classes. Comparative study of normalized percentage of non-glycine and non-proline residues in 3(10), Pi and alpha-helices revealed a considerably higher proportion of 3(10) and Pi-helix residues in disallowed, generous and allowed regions of Ramachandran map. Probe into these findings in the light of evolution suggested clearly that 3(10) and Pi-helices should appropriately be viewed as evolutionary intermediates on long time scale, for not only the α-helical conformation but also for the 'turns', equiprobably. Hence, accidental and random nature of occurrences of 3(10) and Pi-helices, and their evolutionary non-conservation, could be described and explained from an invariant quantitative framework. Extent of correctness of two previously proposed hypotheses on 3(10) and Pi-helices, have been investigated too. Alongside these, a new algorithm to differentiate between related sequences is proposed, which reliably studies evolutionary distance with respect to protein secondary structures.
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