Taylor E W, Agarwal A
Computational Center for Molecular Structure and Design, University of Georgia, Athens 30602-2352.
FEBS Lett. 1993 Jul 5;325(3):161-6. doi: 10.1016/0014-5793(93)81065-8.
Bacteriorhodopsin (BR) is a membrane protein of known structure, widely used for the homology modeling of G-protein-coupled receptors (GPCR). The observation of apparently transposed sequence similarities between some of the helical domains of BR and GPCR has led to the suggestion that exon shuffling may have occurred in the later evolution of GPCR, which would necessitate a different folding pattern for the seven transmembrane helices of GPCR. An alternate hypothesis is that duplication occurred in the evolution of an ancestral gene, such that helices 5-7 originated as duplicates of helices 1-3, leading to intragenic as well as intergenic similarities between helices 1-3 and 5-7 of BR and various GPCR. Analyses of GPCR and BR sequences suggest that such a duplication may have occurred; symmetry within the BR structure is also consistent with homology between these two regions. The hypothesis of evolution by duplication is consistent with the conventional, unshuffled homology model, which is also supported by the obvious conservation of the retinal binding Lys moiety on helix 7 in both BR and the mammalian opsins.
细菌视紫红质（BR）是一种结构已知的膜蛋白，广泛用于G蛋白偶联受体（GPCR）的同源建模。观察到BR的一些螺旋结构域与GPCR之间明显的序列相似性发生了转位，这表明外显子重排可能发生在GPCR的后期进化过程中，这将使GPCR的七个跨膜螺旋需要不同的折叠模式。另一种假设是，在一个祖先基因的进化过程中发生了复制，使得螺旋5-7起源于螺旋1-3的复制，导致BR和各种GPCR的螺旋1-3与5-7之间存在基因内以及基因间的相似性。对GPCR和BR序列的分析表明可能发生了这样的复制；BR结构内的对称性也与这两个区域之间的同源性一致。复制进化假说与传统的、未重排的同源模型一致，BR和哺乳动物视蛋白中螺旋7上视网膜结合赖氨酸部分的明显保守性也支持了这一模型。
