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首页> 外文期刊>Biochemistry >Structural and Spectroscopic Consequences of Hexacoordination of a Bacteriochlorophyll Cofactor in the Rhodobacter sphaeroides Reaction Center,
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Structural and Spectroscopic Consequences of Hexacoordination of a Bacteriochlorophyll Cofactor in the Rhodobacter sphaeroides Reaction Center,

机译：球形红球菌反应中心中细菌叶绿素辅因子的六配位的结构和光谱结果，

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The structural and functional consequences of changing the coordination state of one of thenbacteriochlorophyll (BChl) cofactors in the purple bacterial reaction center have been explored. Ancombination of steady state spectroscopy and X-ray crystallography was used to demonstrate thatnmutagenesis of residue 181 of the L-polypeptide from Phe to Arg (FL181R) causes the BChl at the accessoryn(BB) position on the so-called inactive cofactor branch to become hexacoordinated, with no significantnchanges to the structure of the surrounding protein. This change was accompanied by the appearance of andistinctive absorbance band at 631 nm in the room-temperature absorbance spectrum. The ligand donor wasnnot the Arg side chain but rather an intervening water molecule, and contrary to expectations, the Mg of BBndid not adopt a more in-plane geometry in response to hexacoordination. The mutation caused a disturbancento the detailed conformation of the BChl macrocycle that manifested in a number of subtle changes to thenresonance Raman spectrum. Hexacoordination of BB produced a small increase in the lifetime of the excitednelectronic state of the primary donor bacteriochlorophylls (P*), indicating some disturbance to light-drivennenergy and/or electron transfer events on the time scale of a few picoseconds after light excitation. The BBnbacteriochlorophyll returned to a pentacoordinated state in a doublemutantwhere the FL181Rmutation wasncombined with removal of the native axial ligand through mutation of His M182 to Leu. Experimentalnevidence of hexacoordinated bacteriochlorophylls in the literature on antenna proteins is considered, andnpossible reasons why hexacoordinated bacteriochlorophylls and chlorophylls appear to be avoided innphotosynthetic proteins are discussed.
机译：研究了改变紫色细菌反应中心中一种细菌叶绿素（BChl）辅因子的配位状态的结构和功能后果。稳态光谱学和X射线晶体学的结合用于证明L多肽残基181从Phe到Arg（FL181R）的诱变导致所谓的非活性辅因子分支的antn（BB）位置的BChl变为六配位，周围蛋白质的结构无明显变化。该变化伴随着室温吸收光谱中631nm处的吸收吸收带的出现。配体供体不是Arg侧链，而是中间的水分子，与预期相反，BBndid的Mg对六配位反应没有采用更面内的几何形状。该突变引起对BChl大环的详细构象的干扰，该构象表现为随后的共振拉曼光谱的许多细微变化。 BB的六配位作用使初级供体细菌叶绿素（P *）的激发电子状态的寿命略有增加，这表明在光激发后几皮秒的时间范围内，对光驱动能和/或电子转移事件产生了一些干扰。 BBn叶绿素在双突变体中恢复到五配位状态，其中FL181R突变与通过将His M182突变为Leu去除了天然的轴向配体相结合。考虑到天线蛋白上六配位细菌叶绿素的实验证据，并讨论了在光合蛋白中避免避免六配位细菌叶绿素和叶绿素的可能原因。

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    《Biochemistry》 |2010年第9期|p.1882-1892|共11页
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    Dmitrij Frolov May Marsh Lucy I. Crouch Paul K. Fyfe Bruno Robert Rienk van Grondelle Andrea Hadfield and Michael R. Jones;

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    §Department of Physics and Astronomy, Free University of Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands,) Department of Biochemistry, School ofMedical Sciences, University of Bristol, UniversityWalk, Bristol BS8 1TD, United Kingdom,and ^Service de Biophysique des FonctionsMembranaires,DBJC/CEA and URA 2096/CNRS, CEA-Saclay, F-91191 Gif-sur-Yvette,France@ Present address: Department of Biochemistry, University of Cambridge, 80 Tennis Court Rd., Cambridge CB2 1GA,United Kingdom.#Present address: Division of Biological Chemistry and Drug Discovery, Faculty of LifeSciences, University of Dundee, Nethergate, Dundee DD1 4HN, United Kingdom.;

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