MOLECULAR CHARACTERIZATION OF A SURFACE-EXPOSED SUPEROXIDE-DISMUTASE OF MYCOBACTERIUM-AVIUM

Mycobacterium avium is an intracellular pathogen capable of growing in side the phagosomal compartment of macrophages. In this work, we chara cterized the superoxide dismutase of M. avium, as a putative candidate to resist the oxidative stress. The gene sodA encoding superoxide dis mutase (SOD:EC1.15.1.1) from Mycobacterium avium TMC724 was cloned and sequenced. It encodes a 23 kDa protein (207 aminoacids) showing ident ity with the Mycobacterium leprae SOD (91%) and the M. tuberculosis SO D (83%). This enzyme was functionally expressed in both Escherichia co li and Mycobacterium smegmatis, and identified as a manganese (Mn) SOD on the basis of sequence comparison with other MnSODs from different organisms, and by activity inhibition studies. By indirect immunogold labeling of M. avium with a mAb directed against M. leprae SOD, the en zyme was found to be exposed at the cell surface of M. avium. It was a lso shown that SOD was released in supernates of M. avium TMV724 durin g exponential growth, suggesting a role of this enzyme during interact ions with the environment. When SOD was expressed in the non-pathogeni c M. smegmatis, it was also exposed at the surface of bacteria and rel eased in supernates, but this was not sufficient to protect this recom binant mycobacterium from the killing mechanisms of macrophages. (C) 1 996 Academic Press Limited.