Regulation of the Primary Quinone Binding Conformation by the H Subunit in Reaction Centers from Rhodobacter sphaeroides

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• 作者：Chang Sun ; Alexander T. Taguchi ; Nathan J. Beal ; Patrick J. O鈥橫alley ; Sergei A. Dikanov ; Colin A. Wraight
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2015
• 出版时间：November 19, 2015
• 年：2015
• 卷：6
• 期：22
• 页码：4541-4546
• 全文大小：360K
• ISSN：1948-7185

文摘

Unlike photosystem II (PSII) in higher plants, bacterial photosynthetic reaction centers (bRCs) from Proteobacteria have an additional peripheral membrane subunit 鈥淗鈥? The H subunit is necessary for photosynthetic growth, but can be removed chemically in vitro. The remaining LM dimer retains its activity to perform light-induced charge separation. Here we investigate the influence of the H subunit on interactions between the primary semiquinone and the protein matrix, using a combination of site-specific isotope labeling, pulsed electron paramagnetic resonance (EPR), and density functional theory (DFT) calculations. The data reveal substantially weaker binding interactions between the primary semiquinone and the LM dimer than observed for the intact bRC; the amount of electron spin transferred to the nitrogen hydrogen bond donors is significantly reduced, the methoxy groups are more free to rotate, and the spectra indicate a heterogeneous mixture of bound semiquinone states. These results are consistent with a loosening of the primary quinone binding pocket in the absence of the H subunit.