tailieunhanh - Báo cáo Y học: Thermostability of manganese- and iron-superoxide dismutases from Escherichia coli is determined by the characteristic position of a glutamine residue

The structurally homologous mononuclear iron and man-ganese superoxide dismutases (FeSOD and MnSOD, respectively) containa highly conservedglutamine residue in the active site which projects toward the active-site metal centre and participates in an extensive hydrogen bonding network. The position of this residue is different for each SOD isoenzyme (Q69 in FeSOD and Q146 in MnSOD of Escherichia coli). | Eur. J. Biochem. 269 5137-5148 2002 FEBS 2002 doi Thermostability of manganese- and iron-superoxide dismutases from Escherichia coli is determined by the characteristic position of a glutamine residue Therese Hunter1 Joe V. Bannister1 2 and Gary J. Hunter1 1Department of Physiology and Biochemistry University of Malta Msida Malta 2Cranfield Biotechnology Centre Institute of BioScience and Technology Cranfield University Silsoe Bedfordshire UK The structurally homologous mononuclear iron and manganese superoxide dismutases FeSOD and MnSOD respectively contain a highly conserved glutamine residue in the active site which projects toward the active-site metal centre and participates in an extensive hydrogen bonding network. The position of this residue is different for each SOD isoenzyme Q69 in FeSOD and Q146 in MnSOD of Escherichia coli . Although site-directed mutant enzymes lacking this glutamine residue FeSOD Q69G and MnSOD Q146A demonstrated a higher degree of selectivity for their respective metal they showed little or no activity compared with wild types. FeSOD double mutants FeSOD Q69G A141Q which mimic the glutamine position in MnSOD elicited 25 the activity of wild-type FeSOD while the activity of the corresponding MnSOD double mutant MnSOD G77Q Q146A increased to 150 relative to wild-type MnSOD . Both double mutants showed reduced selectivity toward their metal. Differences exhibited in the thermostability of SOD activity was most obvious in the mutants that contained two glutamine residues FeSOD A141Q and MnSOD G77Q where the MnSOD mutant was thermostable and the FeSOD mutant was thermolabile. Significantly the MnSOD double mutant exhibited a thermal-inactivation profile similar to that of wild-type FeSOD while that of the FeSOD double mutant was similar to wild-type MnSOD. We conclude therefore that the position of this glutamine residue contributes to metal selectivity and is responsible for some of the different .