Proton Uptake in the Reaction Center Mutant L210DN from Rhodobacter sphaeroides via Protonated Water Molecules

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• 作者：Sabine Hermes ; Joanna M. Stachnik ; Delphine Onidas ; André ; Remy ; Eckhard Hofmann ; Klaus Gerwert
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：November 21, 2006
• 年：2006
• 卷：45
• 期：46
• 页码：13741 - 13749
• 全文大小：298K
• 年卷期：v.45,no.46(November 21, 2006)
• ISSN：1520-4995

文摘

The reaction center (RC) of Rhodobacter sphaeroides uses light energy to reduce and protonatea quinone molecule, Q_B (the secondary quinone electron acceptor), to form quinol, Q_BH₂. Asp210 in theL-subunit has been shown to be a catalytic residue in this process. Mutation of Asp210 to Asn leads toa deceleration of reoxidation of Q_A^- in the Q_A^-Q_B Q_AQ_B^- transition. Here we determined the structureof the Asp210 to Asn mutant to 2.5 Å and show that there are no major structural differences as comparedto the wild-type protein. We found Q_B in the distal position and a chain of water molecules betweenAsn210 and Q_B. Using time-resolved Fourier transform infrared (trFTIR) spectroscopy, we characterizedthe molecular reaction mechanism of this mutant. We found that Q_B^- formation precedes Q_A^- oxidationeven more pronounced than in the wild-type reaction center. Continuum absorbance changes indicatedeprotonation of a protonated water cluster, most likely of the water chain between Asn210 and Q_B. Adetailed analysis of wild-type structures revealed a highly conserved water chain between Asp210 orGlu210 and Q_B in Rb. sphaeroides and Rhodopseudomonas viridis, respectively.