Resonance raman characterization of reaction centers with an Asp residue near the photoactive bacteriopheophytin.
Resonance raman characterization of reaction centers with an Asp residue near the photoactive bacteriopheophytin.
复制标题
光活性细菌脱镁叶绿素附近具有 Asp 残基的反应中心的共振拉曼表征。
DOI：
10.1021/bi972410e
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Bocian,DF
中科院分区：
文献类型：
--
作者：
Cua,A;Kirmaier,C;Holten,D;Bocian,DF
报道了一系列含有L多肽第121位突变的红细菌被膜反应中心的QY激发共振拉曼光谱研究。这些研究集中在用Asp残基取代天然Phe引起的BPhL的电子/结构微扰。早期的工作表明，F(L121)D RCS的电子转移性质与BPhL被细菌叶绿素(BCHL)(β-型RCS)或叶绿素取代的RCS的电子转移性质密切相关。除了F(L121)D单突变体外，还对F(L121)D/E(L104)L双突变体进行了RR研究，该双突变体额外地消除了Bp之间的氢键，使天然Glu L104残基成为可能。比较了含有天冬氨酸L121的单突变体和双突变体的振动特征，以及与野生型和F(L121)L RCS的振动特征。用Leu取代芳香族Phe残基对BPhL的振动性质没有明显的影响，这一发现与之前报道的突变对RC的电子转移特性没有影响是一致的。相反，用天冬氨酸取代Phe显著扰乱了BPhL的振动特性，并且以与天冬氨酸L121去质子化和带负电荷最一致的方式。天冬氨酸L121的羧基的负电荷与BPhLin的π-电子系统以一种相对非特异的方式相互作用，减弱了C9-酮基的电荷分离共振形式对辅因子电子结构的贡献。BPhL附近的负电荷的存在与已知的F(L121)D RCS的光化学一致，这表明P+BPhL-的自由能明显高于野生型RCS。
Qy-excitation resonance Raman (RR) studies are reported for a series ofRhodobacter capsulatusreaction centers (RCs) containing mutations at L-polypeptide residue 121 near the photoactive bacteriopheophytin (BPhL). The studies focus on the electronic/structural perturbations of BPhLinduced by replacing the native Phe with an Asp residue. Earlier work has shown that the electron-transfer properties of F(L121)D RCs are closely related to those of RCs in which BPhLis replaced by bacteriochlorophyll (BChl) (beta-type RCs) or by pheophytin. In addition to the F(L121)D single mutant, RR studies were performed on the F(L121)D/E(L104)L double mutant, which additionally removes the hydrogen bond between BPhLand the native Glu L104 residue. The vibrational signatures of BPhLin the single and double mutants containing Asp L121 are compared with one another and with those of BPhLin both wild-type and F(L121)L RCs. The replacement of the aromatic Phe residue with Leu has no discernible effect on the vibrational properties of BPhL, a finding in concert with the previously reported absence of an effect of the mutation on the electron-transfer characteristics of the RC. In contrast, replacement of Phe with Asp significantly perturbs the vibrational characteristics of BPhL, and in a manner most consistent with Asp L121 being deprotonated and negatively charged. The negative charge of the carboxyl group of Asp L121 interacts with the π-electron system of BPhLin a relatively nonspecific fashion, diminishing the contribution of charge-separated resonance forms of the C9-keto group to the electronic structure of the cofactor. The presence of a negative charge near BPhLis consistent with the known photochemistry of F(L121)D RCs, which indicates that the free energy of P+BPhL-is substantially higher than in wild-type RCs.