Chou K C, Maggiora G M, Némethy G, Scheraga H A
Computational Chemistry Unit, Upjohn Company, Kalamazoo, MI 49001.
Proc Natl Acad Sci U S A. 1988 Jun;85(12):4295-9. doi: 10.1073/pnas.85.12.4295.
The main features of the four-alpha-helix bundle, one of the characteristic structural elements of many proteins, can be explained in terms of noncovalent interactions between the constituent helices. Conformational energy computations have been carried out on four types of four-alpha-helix bundles, each consisting of four CH3CO-(L-Ala)10-NHCH3 polypeptide chains, with various combinations of parallel and antiparallel orientations of the helices. In the bundle with the most favorable energy, all pairs of neighboring helices are oriented antiparallel--i.e., in the orientation that is favored by electrostatic interactions between the helices. In this structure, the orientation angle between neighboring helix axes is -168 degrees, within +/- 7 degrees, in close agreement with the orientation angles observed in proteins and with the value that we computed earlier for the most favorable packing of pairs of interacting alpha-helices. This orientation corresponds to a left-handed twisting of the helical bundle. The preferred handedness of this twisting arises as a result of favorable nonbonded interactions between the alpha-helices.
四螺旋束是许多蛋白质的特征性结构元件之一，其主要特征可以用组成螺旋之间的非共价相互作用来解释。已对四种类型的四螺旋束进行了构象能量计算，每种四螺旋束均由四条CH3CO-(L-丙氨酸)10-NHCH3多肽链组成，螺旋具有平行和反平行取向的各种组合。在能量最有利的束中，所有相邻螺旋对均呈反平行取向，即呈螺旋之间静电相互作用所青睐的取向。在这种结构中，相邻螺旋轴之间的取向角为-168度，误差在±7度以内，这与在蛋白质中观察到的取向角以及我们之前计算的相互作用的α螺旋对的最有利堆积值非常一致。这种取向对应于螺旋束的左手扭转。这种扭转的优选手性是α螺旋之间有利的非键相互作用的结果。
