The mycosins of Mycobacterium tuberculosis H37Rv: a family of subtilisin-like serine proteases

There is little information regarding the role of proteolysis in Mycobacter ium tuberculosis and no studies on the potential involvement of proteases i n the pathogenesis of tuberculosis. We identified five M. tuberculosis gene s (mycP1-5) that encode a family of serine proteases (mycosins-1 to 5), ran ging from 36 to 47% identity. Each protein contains a catalytic triad (Asp, His, Ser) within highly conserved sequences, typical of proteases of the s ubtilisin family. These genes are also present in M bovis BCG and other vir ulent mycobacteria, but only one homologue (mycP3) was detected in M. smegm atis. The mycosins have N-terminal signal sequences and C-terminal transmem brane anchors, and the localisation of the mycosins to the membrane/cell wa ll was verified by Western blot analysis of heterologously expressed protei ns in cellular fractions of M. smegmatis. In M. tuberculosis, all the mycos ins were expressed constitutively during growth in broth. Mycosins-2 and 3 were also expressed constitutively in M. bovis BCG, but no expression of my cosin-1 was detected. Mycosin-2 was modified by cleavage in all three mycob acterial species. The multiplicity and constitutive expression of these pro teins suggests that they have an important role in the biology of M. tuberc ulosis. (C) 2000 Elsevier Science B.V. All lights reserved.