Riek R P, Rigoutsos I, Novotny J, Graham R M
Molecular Cardiology Unit Victor Chang Cardiac Research Institute, St Vincent's Hospital, Darlinghurst, New South Wales, 2010, Australia.
J Mol Biol. 2001 Feb 16;306(2):349-62. doi: 10.1006/jmbi.2000.4402.
In "all alpha-fold" transmembrane proteins, including ion channels, G-protein-coupled receptors (GPCRs), bacterial rhodopsins and photosynthetic reaction centers, relatively long alpha-helices, straight, curved or kinked, pack into compact elliptical or circular domains. Using both existing and newly developed tools to analyze transmembrane segments of all available membrane protein three-dimensional structures, including that very recently elucidated for the GPCR, rhodopsin, we report here the finding of frequent non-alpha-helical components, i.e. 3(10)-helices ("tight turns"), pi-helices ("wide turns") and intrahelical kinks (often due to residues other than proline). Often, diverse helical types and kinks concatenate over long segments and produce complex inclinations of helical axis, and/or diverse frame shifts in the "canonical", alpha-helical side-chain pattern. Marked differences in transmembrane architecture exist even between seemingly structurally related proteins, such as bacteriorhodopsin and rhodopsin. Deconvolution of these non-canonical features into their composite elements is essential for understanding the pleiotropy of polytopic protein structure and function, and must be considered in developing valid macromolecular models.
在“全α-折叠”跨膜蛋白中，包括离子通道、G蛋白偶联受体（GPCR）、细菌视紫红质和光合反应中心，相对较长的α-螺旋，笔直的、弯曲的或扭结的，堆积成紧凑的椭圆形或圆形结构域。我们使用现有工具和新开发的工具来分析所有可用膜蛋白三维结构的跨膜片段，包括最近阐明的GPCR视紫红质的结构，在此报告发现了频繁出现的非α-螺旋成分，即3(10)-螺旋（“紧密转角”）、π-螺旋（“宽转角”）和螺旋内扭结（通常由脯氨酸以外的残基引起）。通常，不同类型的螺旋和扭结在长片段上相连，导致螺旋轴产生复杂的倾斜，和/或在“典型”α-螺旋侧链模式中出现不同的移码。即使在看似结构相关的蛋白之间，如细菌视紫红质和视紫红质，跨膜结构也存在显著差异。将这些非典型特征分解为其组成元素对于理解多结构域蛋白结构和功能的多效性至关重要，并且在开发有效的大分子模型时必须加以考虑。
