Tyrosine triad at the interface between the Rieske iron–sulfur protein, cytochrome c1 and cytochrome c2 in the bc1 complex of Rhodobacter capsulatus

• Published in: Biochimica et biophysica acta 2012-05, Vol.1817 (5), p.811-818
• Main Authors: Kyndt, John A., Fitch, John C., Berry, Robert E., Stewart, Matt C., Whitley, Kevin, Meyer, Terry E., Walker, F. Ann, Cusanovich, Michael A.
• Format: Article
• Language: English
• Subjects: alanine; Amino Acid Sequence; Animals; BC1 complex; Biocatalysis; Cytochromes c1 - chemistry; Cytochromes c1 - metabolism; Cytochromes c2 - chemistry; Cytochromes c2 - metabolism; electrochemistry; Electron Transport Complex III - chemistry; Electron Transport Complex III - metabolism; Electrophoresis, Polyacrylamide Gel; heme; Heme - chemistry; Models, Molecular; Molecular Sequence Data; Mutagenesis; mutants; mutation; Mutation - genetics; photosynthesis; Redox potential; Rhodobacter capsulatus; Rhodobacter capsulatus - growth & development; Rhodobacter capsulatus - metabolism; Sequence Alignment; Spectrum Analysis; tyrosine; Tyrosine - metabolism
• ISSN: 0005-2728; 0006-3002; 1879-2650; 0006-3002
• DOI: 10.1016/j.bbabio.2012.01.013

A triad of tyrosine residues (Y152–154) in the cytochrome c1 subunit (C1) of the Rhodobacter capsulatus cytochrome bc1 complex (BC1) is ideally positioned to interact with cytochrome c2 (C2). Mutational analysis of these three tyrosines showed that, of the three, Y154 is the most important, since its mutation to alanine resulted in significantly reduced levels, destabilization, and inactivation of BC1. A second-site revertant of this mutant that regained photosynthetic capacity was found to have acquired two further mutations—A181T and A200V. The Y152Q mutation did not change the spectral or electrochemical properties of C1, and showed wild-type enzymatic C2 reduction rates, indicating that this mutation did not introduce major structural changes in C1 nor affect overall activity. Mutations Y153Q and Y153A, on the other hand, clearly affect the redox properties of C1 (e.g. by lowering the midpoint potential as much as 117mV in Y153Q) and the activity by 90% and 50%, respectively. A more conservative Y153F mutant on the other hand, behaves similarly to wild-type. This underscores the importance of an aromatic residue at position Y153, presumably to maintain close packing with P184, which modeling indicates is likely to stabilize the sixth heme ligand conformation. ► We made six mutants of Rhodobacter capsulatus cytochrome c1. ► Mutant Y152A and Y153F showed no change in redox potential, spectra, or activity. ► Y153Q and Y153A had altered redox potentials and significant loss in activity. ► Close packing of Y153 with P184 is likely to stabilize the sixth heme ligand. ► Mutant Y154A was unstable, but a pseudorevertant arose which regained some activity.