Comparison of Two Yeast MnSODs: Mitochondrial Saccharomyces cerevisiae versus Cytosolic Candida albicans
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- 作者：Yuewei Sheng ; Troy A. Stich ; Kevin Barnese ; Edith B. Gralla ; Duilio Cascio ; R. David Britt ; Diane E. Cabelli ; Joan Selverstone Valentine
- 刊名：Journal of the American Chemical Society
- 出版年：2011
- 出版时间：December 28, 2011
- 年：2011
- 卷：133
- 期：51
- 页码：20878-20889
- 全文大小：1128K
- 年卷期：v.133,no.51(December 28, 2011)
- ISSN：1520-5126
文摘
Human MnSOD is significantly more product-inhibited than bacterial MnSODs at high concentrations of superoxide (O2鈥?/sup>). This behavior limits the amount of H2O2 produced at high [O2鈥?/sup>]; its desirability can be explained by the multiple roles of H2O2 in mammalian cells, particularly its role in signaling. To investigate the mechanism of product inhibition in MnSOD, two yeast MnSODs, one from Saccharomyces cerevisiae mitochondria (ScMnSOD) and the other from Candida albicans cytosol (CaMnSODc), were isolated and characterized. ScMnSOD and CaMnSODc are similar in catalytic kinetics, spectroscopy, and redox chemistry, and they both rest predominantly in the reduced state (unlike most other MnSODs). At high [O2鈥?/sup>], the dismutation efficiencies of the yeast MnSODs surpass those of human and bacterial MnSODs, due to very low level of product inhibition. Optical and parallel-mode electron paramagnetic resonance (EPR) spectra suggest the presence of two Mn3+ species in yeast Mn3+SODs, including the well-characterized 5-coordinate Mn3+ species and a 6-coordinate L鈥揗n3+ species with hydroxide as the putative sixth ligand (L). The first and second coordination spheres of ScMnSOD are more similar to bacterial than to human MnSOD. Gln154, an H-bond donor to the Mn-coordinated solvent molecule, is slightly further away from Mn in yeast MnSODs, which may result in their unusual resting state. Mechanistically, the high efficiency of yeast MnSODs could be ascribed to putative translocation of an outer-sphere solvent molecule, which could destabilize the inhibited complex and enhance proton transfer from protein to peroxide. Our studies on yeast MnSODs indicate the unique nature of human MnSOD in that it predominantly undergoes the inhibited pathway at high [O2鈥?/sup>].