Resonance Raman characterization of H(M200)L mutant reaction centers from Rhodobacter capsulatus. Effects of heterodimer formation on the structural and electronic properties of the cofactors.
Resonance Raman characterization of H(M200)L mutant reaction centers from Rhodobacter capsulatus. Effects of heterodimer formation on the structural and electronic properties of the cofactors.
复制标题
荚膜红杆菌 H(M200)L 突变反应中心的共振拉曼表征。
DOI：
10.1021/bi00035a016
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发表时间：
1995
期刊：
影响因子：
2.9
通讯作者：
Bocian,DF
中科院分区：
文献类型：
--
作者：
Palaniappan,V;Bocian,DF
修订稿于 1995 年 6 月 19 日收到® 摘要：报道了荚膜红杆菌 H (M200) L 突变体的光合反应中心 (RC) 的共振拉曼 (RR) 光谱。在该突变体中，连接野生型 RC 的特殊对主要供体 (P) 的 M 侧细菌叶绿素 (BCh) 的组氨酸残基被非配位亮氨酸取代。这导致异二聚体主要供体 (D) 的形成，其中细菌脱镁叶绿素 (BPh) 取代了 M 侧 BCh。 H (M200) L 突变体的 RR 数据是在大量激发波长下获得的，这些波长跨越 RC 中各种菌绿素辅助因子的 B、Q* 和 Qv 吸收带。为了进行比较，还在相同的激发波长下获取了野生型 RC 的光谱。获得的突变体 RR 数据表明异二聚体形成引起 RC 中辅因子的结构和电子特性的各种变化。这些扰动超出了主要供体的范围，包括两个辅助 BCh 之一。总体而言，RR 研究表明：(1) D [Dl (BCIi)] 中单个 BCh 辅因子的结构与 P 中两个 BCh 中任何一个的结构不同。然而，Dl (BCIi) 与 Pl 比与 Pm 更相似——Pm 辅因子在构象上比 Pl 或 Dl (BCIi) 更扭曲。(2) D [Dm (BPIi)] 中 BPh 辅因子的结构与 RC 中其他两个 BPh 类似。然而，Dm (BPIi) 的 Cg-酮羰基模式的频率异常低 (1678 cm-1)，Pm 的情况也是如此。Dm (BP1i)/Pm 与 DL (BCh)/PL 的 Cg-酮羰基振动的振动特性与介电效应控制模式频率以及初级 L 侧与 M 侧的有效介电常数不同的概念是一致的。 (3) 异二聚体的形成扰乱了 RC 中两个辅助 BChs 之一（最有可能是 BCIil）的结构和电子特性。这些扰动表现为环骨架模式频率的上移和 Q* 吸收带（从 600 到 580 nm）的蓝移。异二聚体扰乱其中一个辅助 BCh 的事实表明，当主要供体中辅因子的配体被去除时，蛋白质基质中会发生整体结构重排。(4) 对于 H (M200) L 突变体和野生型 RC，主要供体的氧化显着影响类胡萝卜素的 RR 横截面。这种效应表明主要供体与类胡萝卜素之间存在很强的相互作用，并表明这些辅助因子之间发生超快能量转移（100 fs 或更少）。类胡萝卜素的 RR 横截面对这些相互作用敏感，这一事实为研究 RC 中类胡萝卜素的 S2 激发态动力学开辟了新途径。细菌光合作用中的主要电子转移过程发生在称为反应中心 (RC) 1 的膜蛋白复合物中（Kirmaier & Holten，1987；Boxer 等，1989；Deisenhofer & Michel，1989a；Feher， 1989；弗里斯纳和温，1989；戴森霍费尔和诺里斯，1993； RC 中的主要电子供体是细菌叶绿素 (BCh) 分子的二聚体 [特殊对 (P)]；主要受体是细菌脱镁叶绿素 (BPh) 分子。 RC 还含有另一种 BPh、两种单体 BCh、一种类胡萝卜素和一个非血红素铁中心。对球形红杆菌和绿色红假单胞菌 RC 的 X 射线晶体学研究表明，P、
Revised Manuscript Received June 19, 1995® abstract: Resonance Raman (RR) spectra are reported for photosynthetic reactionscenters (RCs) from the H (M200) L mutant of Rhodobacter capsulatus. In this mutant, the histidine residue which ligates the M-side bacteriochlorophyll (BCh) of the special pair primary donor (P) of wild-type RCs is replaced by a noncoordinating leucine. This results in the formation of a heterodimer primary donor (D) in which a bacteriopheophytin (BPh) replaces the M-side BCh. The RR data for the H (M200) L mutant were acquired at a large number of excitation wavelengths which span the B, Q*, and Qv absorption bands of the various bacteriochlorin cofactors in the RC. For comparison, spectra were also acquired for wild-type RCs at the same excitation wavelengths. The RR data obtained for the mutant indicate that heterodimerformation induces a variety of changes in the structural and electronic properties of the cofactors in the RC. These perturbations extend beyond the primary donor and include one of the two accessory BChs. Collectively, the RR studies indicate the following:(1) Thestructure of the single BCh cofactor in D [Dl (BCIi)] is different from that of either of the two BChs in P. However, Dl (BCIi) is more similar to Pl than to Pm-The Pm cofactor is conformationally more distorted than either Pl or Dl (BCIi).(2) The structure of the BPh cofactor in D [Dm (BPIi)] is similar to that of the other two BPhs in the RC. However, the frequency of the Cg-keto carbonyl mode of Dm (BPIi) is anomalously low (1678 cm-1), as is also the case for Pm-The vibrational characteristics of the Cg-keto carbonyl vibrations of Dm (BP1i)/Pm versus DL (BCh)/PL are consistent the notion that dielectric effects govern the frequency of the mode and that the effective dielectric constant is different on the L-versus M-sides of the primary donor.(3) Heterodimer formation perturbs the structural and electronic properties of one of the two accessory BChs (most likely BCIil) in the RC. These perturbations are manifested as upshifts in the ring skeletal-mode frequencies and a blue-shift in the Q* absorption band (from 600 to 580 nm). The fact that heterodimerformation perturbs one of the accessory BChs suggests that global structural rearrangements occur in the protein matrix when the ligand to a cofactor in the primary donor is removed.(4) For both the H (M200) L mutant and wild-type RCs, oxidation of the primary donor significantly affects the RR cross section of the carotenoid. This effect indicates strong primary donor—carotenoid interactions and suggest that ultrafast energy transfer (100 fs or less) occurs between these cofactors. The fact that the RR cross section of the carotenoid is sensitive to these interactions opens new avenues for investigating the S2 excited-state dynamics of carotenoids in RCs.The primary electron-transfer processes in bacterialphotosynthesis occur in a membrane protein complex known as the reaction center (RC) 1 (Kirmaier & Holten, 1987; Boxer et al., 1989; Deisenhofer & Michel, 1989a; Feher, 1989; Friesner & Won, 1989; Breton & Verméglio, 1992; Deisenhofer & Norris, 1993). The primary electron donor in RCs is a dimer [the special pair (P)] of bacteriochlorophyll (BCh) molecules; the primary acceptor is a bacteriopheophytin (BPh) molecule. RCs also contain one other BPh, two monomeric BChs, a carotenoid, and a non-heme iron center. X-ray crystallographic studies of RCs from Rhodobacter sphaeroides and Rhodopseudomonas viridis indicate that P,