Carlacci L, Chou K C
Upjohn Research Laboratories, Kalamazoo, MI 49001.
Protein Eng. 1990 May;3(6):509-14. doi: 10.1093/protein/3.6.509.
The packing of four alpha-helices, which each consist of 12 Ala residues and are sequentially connected to each other by a segment of 10 Ala residues, has been investigated by means of energy minimizations. For the lowest energy structure thus obtained, the following features have been found: (i) the four alpha-helices are intimately packed to form an assembly with an approximately square section; (ii) the distances of closest approach between two adjacent interhelix axes are 7.7 +/- 0.2 A and those between two diagonal interhelix axes are 11.2 +/- 0.2 A; (iii) the adjacent interhelix angles are -163 +/- 2 degrees; and (iv) the diagonal interhelix angles are 24 +/- 4 degrees. These results indicate that the polypeptide chain, driven by energetics (nonbonded and electrostatic interactions), is folded into a typical left-handed twisted four-helix bundle with an approximately 4-fold symmetric array, as observed in most four alpha-helix proteins. Furthermore, it has been found that the interaction between the loops formed by the connecting segments and the other part of molecule plays a significant role in stabilizing such a bundle structure. The technology developed here and the relevant knowledge obtained through this study are very useful for the study of modeling four-helix bundle proteins.
通过能量最小化方法研究了由四个α-螺旋组成的结构，每个α-螺旋由12个丙氨酸残基组成，并通过一段10个丙氨酸残基依次相互连接。对于由此获得的能量最低的结构，发现了以下特征：（i）四个α-螺旋紧密堆积形成一个截面近似为正方形的聚集体；（ii）两个相邻螺旋轴之间的最近距离为7.7±0.2 Å，两个对角螺旋轴之间的距离为11.2±0.2 Å；（iii）相邻螺旋间角度为-163±2°；（iv）对角螺旋间角度为24±4°。这些结果表明，在能量（非键合和静电相互作用）的驱动下，多肽链折叠成一个典型的左手扭曲四螺旋束，具有近似四重对称排列，这在大多数四个α-螺旋蛋白中都有观察到。此外，还发现由连接段形成的环与分子的其他部分之间的相互作用在稳定这种束状结构中起着重要作用。这里开发的技术以及通过本研究获得的相关知识对于四螺旋束蛋白的建模研究非常有用。
