The Rv2633c protein of is a non-heme di-iron catalase with a possible role in defenses against oxidative stress.

The gene in is rapidly up-regulated after macrophage infection, suggesting that is involved in pathogenesis. However, the activity and role of the Rv2633c protein in host colonization is unknown. Here, we analyzed the Rv2633c protein sequence, which revealed the presence of an HHE cation-binding domain common in hemerythrin-like proteins. Phylogenetic analysis indicated that Rv2633c is a member of a distinct subset of hemerythrin-like proteins exclusive to mycobacteria. The Rv2633c sequence was significantly similar to protein sequences from other pathogenic strains within that subset, suggesting that these proteins are involved in mycobacteria virulence. We expressed and purified the Rv2633c protein in and found that it contains two iron atoms, but does not behave like a hemerythrin. It migrated as a dimeric protein during size-exclusion chromatography. It was not possible to reduce the protein or observe any evidence for its interaction with O However, Rv2633c did exhibit catalase activity with a of 1475 s and of 10.1 ± 1.7 mm Cyanide and azide inhibited the catalase activity with values of 3.8 μm and 37.7 μm, respectively. Rv2633c's activity was consistent with a role in defenses against oxidative stress generated during host immune responses after infection of macrophages. We note that Rv2633c is the first example of a non-heme di-iron catalase, and conclude that it is a member of a subset of hemerythrin-like proteins exclusive to mycobacteria, with likely roles in protection against host defenses.