We have developed a geometrical approach to quantify differences in the stereochemistry of α-helical and turning regions in four iron proteins. Two spatial signatures are used to analyze residue coordinate data for each protein; and a third is employed to analyze amino-acid molecular volume data. The residue-by-residue analysis of the results, taken together with the finding that two major factors stabilize an α-helix (minimization of side-chain steric interference and intrachain H-bonding), lead to the conclusion that certain residues are preferentially selected for α-helix formation. In the sequential, de novo synthesis of a turning region, residues are preferentially selected such that the overall molecular volume profile (representing purely repulsive, excluded-volume effects) spans a small range Δ of values (Δ = 39.1 Å3) relative to the total range that could be spanned (Δ = 167.7 Å3). It follows that excluded-volume effects are of enormous importance for residues in helical regions as well as those in adjacent turning regions. Once steric effects are taken into account, down-range attractive interactions between residues come into play in the formation of α-helical regions. The geometry of α-helices can be accommodated by conformational changes in less-structured turning regions of a polypeptide, thereby producing a globally optimized (native) protein structure.

中文翻译：

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螺旋蛋白质转向区域中残基的立体化学。

我们已经开发出了一种几何方法来量化四种铁蛋白中α-螺旋和转向区域的立体化学差异。两个空间特征用于分析每种蛋白质的残基坐标数据；第三是分析氨基酸分子体积数据。结果的逐个残基分析，以及两个主要因素稳定α-螺旋（最小化侧链空间干扰和链内H键）的发现，得出以下结论：优先选择某些残基形成α-螺旋。在转向区域的顺序，从头合成中，应优先选择残基，以使总分子体积分布图（代表纯排斥力，排除体积的影响）跨越值的小范围Δ（Δ= 39）。相对于可跨越的总范围（Δ= 167.7Å3）1Å3）。因此，对于螺旋区域以及相邻车削区域中的残渣，排除体积的影响极为重要。一旦考虑到空间效应，则残基之间的低范围吸引相互作用将在α螺旋区的形成中发挥作用。α-螺旋的几何结构可以通过多肽的结构较少的转向区域中的构象变化来适应，从而产生整体优化的（天然）蛋白质结构。残基之间的低范围吸引相互作用在α-螺旋区的形成中起作用。α-螺旋的几何形状可以通过多肽的结构较少的转向区域中的构象变化来适应，从而产生整体优化的（天然）蛋白质结构。残基之间的低范围吸引相互作用在α-螺旋区的形成中起作用。α-螺旋的几何结构可以通过多肽的结构较少的转向区域中的构象变化来适应，从而产生整体优化的（天然）蛋白质结构。