The leader sequence of Mycobacterium tuberculosis Cu,Zn superoxide dismutase (Cu,ZnSOD) contains a prokaryotic membrane lipoprotein attachment site. In the present study, we have found that the protein, which exhibits detectable SOD activity, is lipid-modified and associated with the bacterial membrane when expressed either in M. tuberculosis or in Escherichia coli. These results provide the first demonstration of lipid modification of a Cu,ZnSOD. An analysis of the sodC genes present in available databases indicates that the same signal for lipid modification is also present in the sodC gene products from other mycobacteria and Gram-positive bacteria and, uniquely, in two distinct sodC gene products from the Gram-negative bacterium Salmonella typhimurium. Evidence is also provided for an up-regulation of M. tuberculosis sodC in response to phagocytosis by human macrophages, suggesting that Cu,ZnSOD is involved in the mechanisms that facilitate mycobacterial intracellular growth.
Abbreviations used: MOI, multiplicities of infection; RT-PCR, reverse transcriptase-PCR; SOD, superoxide dismutase.