Ramakrishnan C, Srinivasan N, Prashanth D
Int J Pept Protein Res. 1987 May;29(5):629-37. doi: 10.1111/j.1399-3011.1987.tb02293.x.
Glycine is unique among the amino acids in view of its symmetric nature. While the overall distribution of glycyl residues in the (phi, psi) plane is near-symmetric, there can be certain preferences for the individual conformations. An analysis of the observed glycyl conformations in 70 proteins has been carried out to find the influence of residues adjoining the glycyl residues. For this purpose, the (phi, psi) plane has been divided into two regions: the region in which phi is negative and the region in which phi is positive. The analysis is done in terms of the number of conformations occurring in these regions. It has been found that while the overall percentage distribution of glycyl residues between the positive and the negative phi regions is 54:46, the distribution shows asymmetry when the examples are sorted out in terms of X-Gly and Gly-Y doublets. The asymmetry becomes more prominent when the data are sorted out into triplets X-Gly-Y. Using the available information, it has been possible to designate 25 triplets as P-predominant and 19 as N-predominant. An examination of P-predominant triplets for possible occurrence in beta-bends having one of the conformations in the positive phi region shows that only 25% are of this nature. Thus, the P-preference of P-predominant triplets is not an outcome of the bend formation alone and must be an inherent property of these triplets.
甘氨酸因其对称性质在氨基酸中独具特色。虽然甘氨酰残基在（φ，ψ）平面上的总体分布近乎对称，但各个构象可能存在某些偏好。对70种蛋白质中观察到的甘氨酰构象进行了分析，以探究与甘氨酰残基相邻的残基的影响。为此，（φ，ψ）平面被划分为两个区域：φ为负的区域和φ为正的区域。分析是根据这些区域中出现的构象数量进行的。研究发现，虽然甘氨酰残基在正φ区域和负φ区域之间的总体百分比分布为54:46，但当按照X - Gly和Gly - Y双峰进行分类时，分布呈现出不对称性。当数据被分类为三联体X - Gly - Y时，这种不对称性变得更加明显。利用现有信息，已将25个三联体指定为P型占主导，19个为N型占主导。对可能出现在正φ区域具有构象之一的β - 转角中的P型占主导三联体进行检查发现，只有25%具有这种性质。因此，P型占主导三联体的P偏好并非仅由转角形成导致，而必定是这些三联体的固有属性。
