Glaeser R M, Downing K H, Jap B K
Division of Cell and Molecular Biology, Lawrence Berkeley Laboratory, University of California, Berkeley 94720.
Biophys J. 1991 Apr;59(4):934-8. doi: 10.1016/S0006-3495(91)82307-4.
The recently published model of the structure of bacteriorhodopsin (bR), developed by fitting the peptide chain to a high-resolution, three-dimensional density map, rules out the existence of transmembrane beta-sheet and provides an accurate estimate of the helix content. The precise geometry of the dihedral angles in the helical regions of the polypeptide cannot yet be specified from the diffraction data, however. Published data on the circular dichroism (CD) spectrum between 190 and 240 nm, and the infrared (IR) spectrum in the amide I band suggest that the helical conformation in bR may be, for the most part, a rather unusual one. The precise structural model, which specifies the number of residues in transmembrane helices, can now be used as an additional constraint in seeking models of the helical conformation that are in quantitative agreement with the CD and IR spectroscopic data. Further spectroscopic measurements can also be used to determine whether there are changes in the unusual dihedral-angle conformation within the helices during the photocycle.
最近发表的细菌视紫红质（bR）结构模型，是通过将肽链拟合到高分辨率三维密度图而构建的，该模型排除了跨膜β-折叠的存在，并对螺旋含量进行了准确估计。然而，从衍射数据尚无法确定多肽螺旋区域中二面角的精确几何形状。已发表的关于190至240纳米之间的圆二色性（CD）光谱以及酰胺I带中的红外（IR）光谱的数据表明，bR中的螺旋构象在很大程度上可能是一种相当不寻常的构象。现在，指定跨膜螺旋中残基数量的精确结构模型可作为一个额外的约束条件，用于寻找与CD和IR光谱数据在数量上一致的螺旋构象模型。进一步的光谱测量还可用于确定在光循环过程中螺旋内异常二面角构象是否发生变化。
