Matsuno M, Takeuchi H, Overman S A, Thomas G J
Pharmaceutical Institute, Tohoku University, Sendai, Japan.
Biophys J. 1998 Jun;74(6):3217-25. doi: 10.1016/S0006-3495(98)78028-2.
Virions of the Ff group of bacteriophages (fd, f1, M13) are morphologically identical filaments (approximately 6-nm diameter x approximately 880-nm length) in which a covalently closed, single-stranded DNA genome is sheathed by approximately 2700 copies of a 50-residue alpha-helical subunit (pVIII). Orientations of pVIII tyrosines (Tyr21 and Tyr24) with respect to the filament axis have been determined by Raman linear intensity difference (RLID) spectroscopy of flow-oriented mutant virions in which the tyrosines were independently mutated to methionine. The results show that the twofold axis of the phenolic ring (C1-C4 line) of Tyr21 is inclined at 39.5 +/- 1.4 degrees from the virion axis, and that of Tyr24 is inclined at 43.7 +/- 0.6 degrees. The orientation determined for the Tyr21 phenol ring is close to that of a structural model previously proposed on the basis of fiber x-ray diffraction results (Protein Data Bank, identification code 1IFJ). On the other hand, the orientation determined for the Tyr24 phenol ring differs from the diffraction-based model by a 40 degrees rotation about the Calpha-Cbeta bond. The RLID results also indicate that each tyrosine mutation does not greatly affect the orientation of either the remaining tyrosine or single tryptophan (Trp26) of pVIII. On the basis of these results, a refined model is proposed for the coat protein structure in Ff.
噬菌体Ff组（fd、f1、M13）的病毒粒子在形态上是相同的丝状结构（直径约6纳米×长度约880纳米），其中一个共价闭合的单链DNA基因组被大约2700个50个残基的α-螺旋亚基（pVIII）包裹。通过对酪氨酸分别突变为甲硫氨酸的流动取向突变病毒粒子进行拉曼线性强度差（RLID）光谱分析，确定了pVIII酪氨酸（Tyr21和Tyr24）相对于丝状轴的取向。结果表明，Tyr21酚环（C1-C4线）的二重轴与病毒粒子轴的夹角为39.5±1.4度，Tyr24的夹角为43.7±0.6度。为Tyr21酚环确定的取向与先前基于纤维X射线衍射结果提出的结构模型（蛋白质数据库，识别码1IFJ）相近。另一方面，为Tyr24酚环确定的取向与基于衍射的模型相比，绕Cα-Cβ键旋转了40度。RLID结果还表明，每个酪氨酸突变对pVIII中剩余酪氨酸或单个色氨酸（Trp26）的取向影响不大。基于这些结果，提出了一个Ff外壳蛋白结构的精细模型。
