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首页> 外文期刊>Biochemistry >Evidence for hydrogen bond formation to the PsaB chlorophyll of P700 in photosystem I mutants of Synechocystis sp PCC 6803
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Evidence for hydrogen bond formation to the PsaB chlorophyll of P700 in photosystem I mutants of Synechocystis sp PCC 6803

机译：在Synechocystis sp PCC 6803光系统I突变体中，P700的PsaB叶绿素形成氢键的证据。

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摘要

P700, the primary electron donor of photosystem 1, is an asymmetric dimer made of one molecule of chlorophyll a' (P-A) and one of chlorophyll a (P-B) that are bound to the homologous PsaA and PsaB polypeptides. While the carbonyl groups of PA are involved in hydrogen-bonding interactions with several surrounding amino acid side chains and a water molecule, P-B does not engage hydrogen bonds with the protein. Notably, the residue Thr A739 is donating a strong hydrogen bond to the 9-keto C=O group Of PA and the homologous residue Tyr B718 is free from interaction with P-B. Light-induced FTIR difference spectroscopy of the photooxidation of P700 has been combined with a site-directed mutagenesis attempt to introduce hydrogen bonds to the carbonyl groups Of PB in Synechocystis sp. PCC 6803. The FTIR study of the Y(B718)T mutant provides evidence that the 9-keto C=O group Of P-B and P-B(+) engages a relatively strong hydrogen-bonding interaction with the surroundings in a significant fraction (40 10%) of the reaction centers. Additional mutations on the two PsaB residues homologous to those involved in the main interactions between the PsaA polypeptide and the 10a-carbomethoxy groups Of P-A affect only marginally the vibrational frequency of the 10a-ester C=O group of P-B. The FTIR data on single, double, and triple mutants at these PsaB sites indicate a plasticity of the interactions of the carboryl groups Of PB with the surrounding protein. However, these mutations do not perturb the hydrogen-bonding interactions assumed by the 9-keto and 10a-ester C=O groups Of P-A and P-A(+) with the protein and have only a limited effect on the relative charge distribution between P-A(+) and P-B(+).
机译：P700是光系统1的主要电子供体，是一种不对称的二聚体，由与同源PsaA和PsaB多肽结合的一分子叶绿素a'（P-A）和叶绿素a（P-B）组成。当PA的羰基与周围的几个氨基酸侧链和水分子发生氢键相互作用时，P-B不会与蛋白质发生氢键结合。值得注意的是，残基Thr A739正在向PA的9-酮C ＝ O基团提供强氢键，而同源残基Tyr B718没有与P-B相互作用。 P700的光氧化的光诱导FTIR差异光谱已与定点诱变结合，试图将氢键引入到Synechocystis sp。的PB羰基中。 PCC6803。对Y（B718）T突变体的FTIR研究提供了证据，表明PB和PB（+）的9-酮C = O基团与周围环境发生了较强的氢键相互作用（40 10 ％）的反应中心。与PsaA多肽和P-A的10a-甲氧基甲氧基之间的主要相互作用涉及的两个PsaB残基同源的其他突变，仅对P-B的10a-酯C = O基团的振动频率产生微小影响。在这些PsaB位点上的单，双和三突变体的FTIR数据表明PB的碳硼基与周围蛋白质的相互作用具有可塑性。但是，这些突变不会干扰由PA和PA（+）的9-酮基和10a-酯C = O基团与蛋白质形成的氢键相互作用，并且对PA（ +）和PB（+）。

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