Location of a cytochrome c binding site on the surface of flavocytochrome b
2 |
| |
Authors: | Duncan M Short Malcolm D Walkinshaw Paul Taylor Graeme A Reid S K Chapman |
| |
Institution: | (1) Department of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, Scotland, UK Tel. & Fax: +44-131-650-4760; e-mail: S.K.Chapman@ed.ac.uk, GB;(2) Department of Biochemistry, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, Scotland, UK, GB;(3) Institute of Cell and Molecular Biology, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, Scotland, UK, GB |
| |
Abstract: | Saccharomyces cerevisiae flavocytochrome b 2 couples the oxidation of L-lactate to the reduction of cytochrome c. The second-order rate constant for cytochrome c reduction by flavocytochrome b 2 depends on the rate of complex formation and is sensitive to ionic strength. Mutations in the heme domain of flavocytochrome b 2 (Glu63→Lys, Asp72→Lys and the double mutation Glu63→Lys:Asp72→Lys) have significant effects on the reaction with cytochrome c, implicating these residues in complex formation. This kinetic information has been used to guide molecular modelling studies, which are consistent with there being no one single best-configuration. Rather, there is a set of possible complexes in which the docking-face of cytochrome c can approach flavocytochrome b 2 in a variety of orientations. Four cytochromes c can be accommodated on the flavocytochrome b 2 tetramer, with each cytochrome c forming interactions with only one flavocytochrome b 2 subunit. All the models involve residues 72 and 63 on flavocytochrome b 2 but in addition predict that Glu237 may also be important for complex formation. These acidic residues interact with the basic residues 13, 27 and 79 on cytochrome c. Through this triangle of interactions runs a possible σ-tunnelling pathway for electron transfer. This pathway starts with the imidazole ring of His66 (a ligand to the heme-iron of flavocytochrome b 2) and ends with the ring of Pro68, which is in van der Waals contact with the cytochrome c heme. In total, the edge-to-edge "through space" distance from the imidazole ring of His66 to the C3C pyrrole ring of cytochrome c is 13.1?Å. |
| |
Keywords: | Flavocytochrome b2 Cytochrome c Electron transfer Modelling site-directed mutagenesis |
本文献已被 SpringerLink 等数据库收录! |
|