Manganese superoxide dismutase (MnSOD) is a dimer in bacteria and a tetramer in mitochondria of eukaryotes. In order to investigate the evolutionary significance of the transition from dimer to tetramer, two yeast MnSODs, one from Saccharomyces cerevisiae mitochondria (ScMnSOD) and the other from Candida albicans cytosol (CaMnSODc), were characterized. ScMnSOD is a tetramer, while CaMnSODc can either be a dimer or a tetramer depending on solution conditions. This difference is likely due to distinct hydrogen bonding at the tetramer inferface of ScMnSOD and CaMnSODc. The tetrameric structure renders ScMnSOD much more resistance to heat and denaturant than the dimeric structure does to CaMnSODc. Mutations of two dimer interface residues caused significant loss of stability, resulting in higher sensitivity to pH, heat and denaturant in the mutant of dimeric CaMnSODc, but not in that of tetramric ScMnSOD. Therefore, the tetrameric structure also reinforces the integrity of MnSOD dimer interface.

Tetramer vs. dimer: The evolutionary significance of the quaternary structure of MnSOD

243rd National Meeting (2012)

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