Findlay J B, Barclay P L, Brett M, Davison M, Pappin D J, Thompson P
Vision Res. 1984;24(11):1501-8. doi: 10.1016/0042-6989(84)90312-2.
Ovine rhodopsin is organised in disc membranes as a monomer. The determination of its amino acid sequence has permitted the utilisation of structure prediction programmes which indicate the probable disposition of the polypeptide chain in the bilayer. This putative model is consistent with labelling data using the chemical probes, [14C]succinic anhydride, [125I]diazodiido sulphanilic acid and [125I]iodophenyl azide, and with the cleavage points for several proteases. More surprisingly the predicted structure points to the occurrence of breaks/distortions in the transmembrane helical segments. These distorted regions may be of primary functional importance to the protein and at least one is associated with the attachment point of the chromophore. This particular part of the structure is also identified as a "mutational hot spot", for bovine, equine, ovine and porcine opsins exhibit different sequences (but conserved molecular volumes) in the four residues following the retinyllysine. In an otherwise highly conserved protein with no obvious functional differences between the four species, the high substitution rate in this region is unexplained.
绵羊视紫红质在盘状膜中以单体形式存在。其氨基酸序列的确定使得能够利用结构预测程序，这些程序可指示多肽链在双层膜中的可能排布。这个推测模型与使用化学探针[14C]琥珀酸酐、[125I]重氮二碘磺胺酸和[125I]碘苯叠氮化物的标记数据以及几种蛋白酶的切割位点相符。更令人惊讶的是，预测结构表明跨膜螺旋段存在断裂/扭曲。这些扭曲区域可能对蛋白质具有主要功能重要性，并且至少有一个与发色团的附着点相关。结构的这一特定部分也被确定为一个“突变热点”，因为牛、马、绵羊和猪的视蛋白在视黄醛赖氨酸之后的四个残基中表现出不同的序列（但分子体积保守）。在这四个物种之间没有明显功能差异的高度保守蛋白质中，该区域的高替换率无法解释。
