Bowie J U
Department of Chemistry and Biochemistry, UCLA-DOE 90095-1570, USA.
J Mol Biol. 1997 Oct 10;272(5):780-9. doi: 10.1006/jmbi.1997.1279.
A survey of 45 transmembrane (TM) helices and 88 helix packing interactions in three independent transmembrane protein structures reveals the following features. (1) Helix lengths range from 14 to 36 residues with an average length of 26.4 residues. There is a preference for lengths greater than 20 residues. (2) The helices are tilted with respect to the bilayer normal by an average of 21 degrees, but there is a decided preference for smaller tilt angles. (3) The distribution of helix packing angles is very different than for soluble proteins. The most common packing angles for TM helices are centered around +20 degrees while for soluble proteins packing angles of around -35 degrees are the most prevalent. (4) The average distance of closest approach is 9.6 A, which is the same as soluble proteins. (5) There is no preference for the positioning of the point of closest approach along the length of the helices. (6) It is almost a rule that TM helices pack against neighbors in the sequence. Of the 37 helices that have a sequence neighbor, 36 of them are in significant contact with a neighbor. (7) An antiparallel orientation is more prevalent than a parallel orientation and antiparallel interactions are more intimate on average. The general features of helix bundle membrane protein architecture described in this survey should prove useful in the modeling of helix bundle transmembrane proteins.
对三个独立跨膜蛋白结构中的45个跨膜（TM）螺旋和88个螺旋堆积相互作用进行的一项研究揭示了以下特征。（1）螺旋长度范围为14至36个残基，平均长度为26.4个残基。倾向于长度大于20个残基。（2）螺旋相对于双层法线平均倾斜21度，但明显倾向于较小的倾斜角度。（3）螺旋堆积角的分布与可溶性蛋白质的非常不同。TM螺旋最常见的堆积角集中在+20度左右，而可溶性蛋白质的堆积角在-35度左右最为普遍。（4）最接近的平均距离为9.6埃，与可溶性蛋白质相同。（5）沿着螺旋长度，最接近点的定位没有偏好。（6）TM螺旋几乎总是与序列中的相邻螺旋堆积在一起。在有序列相邻螺旋的37个螺旋中，有36个与相邻螺旋有显著接触。（7）反平行取向比平行取向更普遍，并且反平行相互作用平均更紧密。本研究中描述的螺旋束膜蛋白结构的一般特征在螺旋束跨膜蛋白的建模中应会证明是有用的。
