Tetramerization reinforces the dimer interface of MnSOD.

Two yeast manganese superoxide dismutases (MnSOD), one from Saccharomyces cerevisiae mitochondria (ScMnSOD) and the other from Candida albicans cytosol (CaMnSODc), have most biochemical and biophysical properties in common, yet ScMnSOD is a tetramer and CaMnSODc is a dimer or "loose tetramer" in solution. Although CaMnSODc was found to crystallize as a tetramer, there is no indication from the solution properties that the functionality of CaMnSODc in vivo depends upon the formation of the tetrameric structure. To elucidate further the functional significance of MnSOD quaternary structure, wild-type and mutant forms of ScMnSOD (K182R, A183P mutant) and CaMnSODc (K184R, L185P mutant) with the substitutions at dimer interfaces were analyzed with respect to their oligomeric states and resistance to pH, heat, and denaturant.

Six-coordinate manganese(3+) in catalysis by yeast manganese superoxide dismutase.

Reduction of superoxide (O2-) by manganese-containing superoxide dismutase occurs through either a "prompt protonation" pathway, or an "inner-sphere" pathway, with the latter leading to formation of an observable Mn-peroxo complex. We recently reported that wild-type (WT) manganese superoxide dismutases (MnSODs) from Saccharomyces cerevisiae and Candida albicans are more gated toward the "prompt protonation" pathway than human and bacterial MnSODs and suggested that this could result from small structural changes in the second coordination sphere of manganese. We report here that substitution of a second-sphere residue, Tyr34, by phenylalanine (Y34F) causes the MnSOD from S.