Site-Directed Mutagenesis of PsaA Residue W693 Affects Phylloquinone Binding and Function in the Photosystem I Reaction Center of Chlamydomonas reinhardtii
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- 作者：Saul Purton ; David R. Stevens ; Irine P. Muhiuddin ; Michael C. W. Evans ; Susan Carter ; Stephen E. J. Rigby ; and Peter Heathcote
- 刊名：Biochemistry
- 出版年：2001
- 出版时间：February 20, 2001
- 年：2001
- 卷：40
- 期：7
- 页码：2167 - 2175
- 全文大小：123K
- 年卷期：v.40,no.7(February 20, 2001)
- ISSN：1520-4995
文摘
To investigate the environment of the phylloquinone secondary electron acceptor A1 withinthe photosystem I reaction center, we have carried out site-directed mutagenesis of two tryptophan residues(W693 and W702) in the PsaA subunit of Chlamydomonas reinhardtii. One of these conserved tryptophans(W693) is predicted to be close to the phylloquinone and has been implicated in the interaction of A1with an aromatic residue through 
- stacking. We find that replacement of W702 with either histidineor leucine has no effect on the electronic structure of A1
- or on forward electron transfer from A1- tothe iron-sulfur center Fx. In contrast, the same mutations of W693 alter the electronic structure of thephotoaccumulated A1- and slow forward electron transfer as measured by the decay of the electron spin-polarized signal arising from the P700+/A1- radical pair. These results provide support for the hypothesisthat W693 has a role in poising the redox potential of A1/A1- so it can reduce Fx, and they indirectlyprovide evidence for electron transfer along the PsaA-side branch of cofactors in PSI.
- stacking. We find that replacement of W702 with either histidineor leucine has no effect on the electronic structure of A1- or on forward electron transfer from A1- tothe iron-sulfur center Fx. In contrast, the same mutations of W693 alter the electronic structure of thephotoaccumulated A1- and slow forward electron transfer as measured by the decay of the electron spin-polarized signal arising from the P700+/A1- radical pair. These results provide support for the hypothesisthat W693 has a role in poising the redox potential of A1/A1- so it can reduce Fx, and they indirectlyprovide evidence for electron transfer along the PsaA-side branch of cofactors in PSI.