Surface-modulated motion switch: capture and release of iron-sulfur protein in the cytochrome bc1 complex.
In the cytochrome bc(1) complex, the swivel motion of the iron-sulfur protein (ISP) between two redox sites constitutes a key component of the mechanism that achieves the separation of the two electrons in a substrate molecule at the quinol oxidation (Q(o)) site. The question remaining is how the motion of ISP is controlled so that only one electron enters the thermodynamically favorable chain via ISP. An analysis of eight structures of mitochondrial bc(1) with bound Q(o) site inhibitors revealed that the presence of inhibitors causes a bidirectional repositioning of the cd1 helix in the cytochrome b subunit. As the cd1 helix forms a major part of the ISP binding crater, any positional shift of this helix modulates the ability of cytochrome b to bind ISP. The analysis also suggests a mechanism for reversal of the ISP fixation when the shape complementarity is significantly reduced after a positional reorientation of the reaction product quinone. The importance of shape complementarity in this mechanism was confirmed by functional studies of bc(1) mutants and by a structure determination of the bacterial form of bc(1). A mechanism for the high fidelity of the bifurcated electron transfer is proposed.
Esser
Lothar
L
Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Gong
Xing
X
Yang
Shaoqing
S
Yu
Linda
L
Yu
Chang-An
CA
Xia
Di
D
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D004583:Electrons; D006860:Hydrogen Bonding; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000737:chemistry
D007506:Iron-Sulfur Proteins; D050505:Mutant Proteins; D021122:Protein Subunits; D014450:Electron Transport Complex III