Resonance Raman characterization of reaction centers in which bacteriochlorophyll replaces the photoactive bacteriopheophytin.
Resonance Raman characterization of reaction centers in which bacteriochlorophyll replaces the photoactive bacteriopheophytin.
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反应中心的共振拉曼表征，其中细菌叶绿素取代光活性细菌脱镁叶绿素。
DOI：
10.1021/bi971600m
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
Bocian,DF
中科院分区：
文献类型：
--
作者：
Czarnecki,K;Schenck,CC;Bocian,DF
报道了类球形红细菌（Rhodobacter sphaeroides）中两个突变反应中心（RC）的Q γ激发共振拉曼（RR）光谱。一个突变，（M）L214 H，通过在位置M214处引入组氨酸残基产生色素变化。另一个突变，（M）L214 H/（L）E104 V，去除了β和L104位天然谷氨酸残基之间的假定氢键。将突变体的β L辅因子的振动特征相互比较，并与β-突变体和野生型RC中的辅助BChl（BChlL，M）的振动特征进行比较。光谱数据表明：（1）βLcofactor是一个五配位的BChl分子，轴向配体为组氨酸。β的构象和Mg-组氨酸键的强度与BChlL，M非常相似。(2)β L辅因子以与野生型BPhL类似的方式在蛋白口袋中定向。(3)（M）L214 H突变体的β L辅因子通过大环的C9-酮基与谷氨酸L104形成氢键。该氢键的强度与该蛋白质残基和BPhLin野生型的C9-酮基之间形成的氢键强度相同。(4)在C9-酮位点的氢键相互作用诱导二级辅因子-蛋白质相互作用，涉及C2 a-乙酰基和Cb-烷基取代基。总的来说，β L的振动特征表明其内在物理化学性质与BChlL非常相似。因此，正如Kirmaier等人最初提出的那样，β型RC中最初的电荷分离中间体最好表征为P+β L-和P+BChlL-（P是主要的电子供体）的热/量子力学混合物[（1995）J. Phys. Chem. 99，8903−8909]。
Qy-excitation resonance Raman (RR) spectra are reported for two mutant reactions centers (RCs) fromRhodobacter sphaeroidesin which the photoactive bacteriopheophytin (BPhL) is replaced by a bacteriochlorophyll (BChl) molecule, designated by βL. One mutation, (M)L214H, yields the pigment change via introduction of a histidine residue at position M214. The other mutation, (M)L214H/(L)E104V, removes the putative hydrogen bond between βLand the native glutamic acid residue at position L104. The vibrational signatures of the βLcofactors of the mutants are compared with one another and with those of the accessory BChls (BChlL,M) in both β-mutant and wild-type RCs. The spectroscopic data reveal the following: (1) The βLcofactor is a five-coordinate BChl molecule with a histidine axial ligand. The conformation of βLand the strength of the Mg−histidine bond are very similar to that of BChlL,M. (2) The βLcofactor is oriented in the protein pocket in a manner similar to that of BPhLof wild-type. (3) The βLcofactor of the (M)L214H mutant forms a hydrogen bond with glutamic acid L104 via the C9-keto group of the macrocycle. The strength of this hydrogen bond is identical to that formed between this protein residue and the C9-keto group of BPhLin wild-type. (4) The hydrogen bonding interaction at the C9-keto site induces secondary cofactor−protein interactions which involve the C2a-acetyl and Cb-alkyl substituent groups. Collectively, the vibrational signatures of βLindicate that its intrinsic physicochemical properties are very similar to those of BChlL. Consequently, the initial charge-separated intermediate in β-type RCs is best characterized as a thermal/quantum mechanical admixture of P+βL-and P+BChlL-(P is the primary electron donor), as originally proposed by Kirmaier et al. [(1995)J. Phys. Chem. 99, 8903−8909].