Olsen J D, Sockalingum G D, Robert B, Hunter C N
Krebs Institute for Biomolecular Research, University of Sheffield, United Kingdom.
Proc Natl Acad Sci U S A. 1994 Jul 19;91(15):7124-8. doi: 10.1073/pnas.91.15.7124.
Site-directed mutagenesis has been used to examine the function of a highly conserved aromatic residue, alpha Trp43, in the light-harvesting 1 antenna of the photosynthetic bacterium Rhodobacter sphaeroides. In this antenna alpha Trp43 is thought to be located near the putative binding site for bacteriochlorophyll; in this work it was changed to both Tyr and Phe, and in each case the main near-infrared absorbance peak was shifted to the blue, from 876 nm to 865 nm and then to 853 nm, respectively. Resonance Raman spectroscopy of the resulting complexes shows a shift of one component of the 1640-cm-1 peak to 1632 cm-1 for the Tyr mutant and to 1660 cm-1 for the Phe mutant. This demonstrates a strengthening of an existing H bond for the Tyr change and a breakage of this bond for the change to Phe. The 1640-cm-1 peak has been previously assigned to H-bonded C2 acetyl carbonyl groups of both bacteriochlorophylls in the light-harvesting 1 antenna dimer [Robert, B. & Lutz, M. (1985) Biochim. Biophys. Acta 807, 10-21]. These results indicate that one of these H bonds is to alpha Trp43, placing this residue in close proximity to the bacteriochlorophyll a macrocycle with which it interacts. The existence of this bond places constraints on the conformation of the alpha polypeptide, and a model of an alpha beta heterodimer is presented incorporating these data.
定点诱变已被用于研究光合细菌球形红杆菌光捕获1天线中一个高度保守的芳香族残基αTrp43的功能。在该天线中，αTrp43被认为位于细菌叶绿素的假定结合位点附近；在这项工作中，它被分别替换为Tyr和Phe，并且在每种情况下，主要的近红外吸收峰都向蓝光方向移动，分别从876nm移至865nm，然后再移至853nm。所得复合物的共振拉曼光谱显示，对于Tyr突变体，1640-cm-1峰的一个组分移至1632 cm-1，对于Phe突变体则移至1660 cm-1。这表明对于Tyr的变化，现有氢键得到加强，而对于变为Phe的变化，该氢键断裂。1640-cm-1峰先前已被指定为光捕获1天线二聚体中两种细菌叶绿素的氢键结合的C2乙酰羰基[罗伯特，B.和卢茨，M.（1985年）《生物化学与生物物理学报》807，10 - 21]。这些结果表明其中一个氢键与αTrp43形成，使该残基紧邻与其相互作用的细菌叶绿素a大环。该键的存在对α多肽的构象施加了限制，并提出了一个包含这些数据的αβ异二聚体模型。
