Langosch D, Heringa J
Department of Neurobiology, Universität Heidelberg, Germany.
Proteins. 1998 May 1;31(2):150-9. doi: 10.1002/(sici)1097-0134(19980501)31:2<150::aid-prot5>3.0.co;2-q.
Membrane-embedded protein domains frequently exist as alpha-helical bundles, as exemplified by photosynthetic reaction centers, bacteriorhodopsin, and cytochrome C oxidase. The sidechain packing between their transmembrane helices was investigated by a nearest-neighbor analysis which identified sets of interfacial residues for each analyzed helix-helix interface. For the left-handed helix-helix pairs, the interfacial residues almost exclusively occupy positions a, d, e, or g within a heptad motif (abcdefg) which is repeated two to three times for each interacting helical surface. The connectivity between the interfacial residues of adjacent helices conforms to the knobs-into-holes type of sidechain packing known from soluble coiled coils. These results demonstrate on a quantitative basis that the geometry of sidechain packing is similar for left-handed helix-helix pairs embedded in membranes and coiled coils of soluble proteins. The transmembrane helix-helix interfaces studied are somewhat less compact and regular as compared to soluble coiled coils and tolerate all hydrophobic amino acid types to similar degrees. The results are discussed with respect to previous experimental findings which demonstrate that specific interactions between transmembrane helices are important for membrane protein folding and/or oligomerization.
膜嵌入蛋白结构域常常以α-螺旋束的形式存在，光合反应中心、细菌视紫红质和细胞色素C氧化酶就是例证。通过最近邻分析研究了它们跨膜螺旋之间的侧链堆积情况，该分析为每个分析的螺旋-螺旋界面确定了界面残基集。对于左手螺旋-螺旋对，界面残基几乎只占据七肽基序（abcdefg）中的a、d、e或g位置，每个相互作用的螺旋表面重复两到三次。相邻螺旋的界面残基之间的连接符合可溶性卷曲螺旋中已知的旋钮-入-孔型侧链堆积。这些结果在定量基础上表明，嵌入膜中的左手螺旋-螺旋对和可溶性蛋白质的卷曲螺旋的侧链堆积几何形状相似。与可溶性卷曲螺旋相比，所研究的跨膜螺旋-螺旋界面不太紧密且规则性稍差，并且对所有疏水氨基酸类型的耐受性相似。结合先前的实验结果对这些结果进行了讨论，先前的实验结果表明跨膜螺旋之间的特定相互作用对膜蛋白折叠和/或寡聚化很重要。
