The highly conserved methionine of subunit I of the heme-copper oxidases is not at the heme-copper dinuclear center: Mutagenesis of M110 in subunit I of cytochrome bo3-type ubiquinol oxidase from Escherichia coli

Abstract A common feature within the heme-copper oxidase superfamily is the dinuclear heme-copper center. Analysis via extended X-ray absorption fine structure (EXAFS) has led to the proposal that sulfur may be bound to CU B , a component of the dinuclear center, and a highly conserved methionine (M110 in the E. coli oxidase) in subunit I has been proposed as the ligand. Recent models of subunit I, however, suggest that this residue is unlikely to be near CU B , but is predicted to be near the low spin heme component of the heme-copper oxidases. In this paper, the role of M110 is examined by spectroscopic analyses of site-directed mutants of the bo 3 -type oxidase from Escherichia coli . The results show that M110 is a non-essential residue and suggest that it is probably not near the heme-copper dinuclear center.