A BROWNIAN DYNAMICS STUDY OF THE INTERACTIONS OF THE LUMENAL DOMAINS OF THE CYTOCHROME
B6f COMPLEX WITH PLASTOCYANIN AND CYTOCHROME C6:
THE EFFECTS OF THE RIESKE FES PROTEIN ON THE INTERACTIONS
Esmael J. Haddadian 1 and Elizabeth L. Gross 1*
1 The Ohio State University
* To whom correspondence should be addressed. E-mail: gross.3{at}osu.edu.
Submitted on April 3, 2006
Revised on May 9, 2006
Accepted on 21 June 2006
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Abstract |
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The availability of the structures of the cytochrome b6f complex (cyt b6f), plastocyanin (PC), and cytochrome c6 (cyt c6) from Chlamydomonas reinhardtii allowed us, for the first time, to model electron transfer interactions between the lumenal domains of this complex (including cyt f and the Rieske FeS protein) and its redox partners in the same species. We also generated a model structure, in which the FeS center of the Rieske protein was positioned closer to the heme of cyt f than observed in the crystal structure and studied its interactions with both PC and cyt c6. Our data showed that the Rieske protein in both the original crystal structure and in our modeled structure of the cyt b6f complex did not physically interfere with binding position or orientation of PC or cyt c6 on cyt f. PC docked on cyt f with the same orientation in the presence or the absence of the Rieske protein, which matched well with the previously reported NMR structures of complexes between cyt f and PC. When the FeS center of the Rieske protein was moved close to the heme of cyt f, it even enhanced the interaction rates. Studies using a cyt f modified in #184-191 loop showed that the cyt f structure is a more important factor in determining the rate of complex formations than is the presence or the absence of the Rieske protein, or its position with respect to cyt f.
Key Words:
Brownian Dynamics, Plastocyanin, Rieske, cytochrome c6, cytochrome f, protein interactions
