Expression of the Mycobacterium tuberculosis 19-kilodalton antigen in Mycobacterium smegmatis: Immunological analysis and evidence of glycosylation

The gene encoding a 19-kDa antigen from Mycobacterium tuberculosis was expressed as a recombinant protein in the rapid-growing species Mycobacterium smegmatis. The recombinant antigen was expressed at a level approximately ninefold higher than in M. tuberculosis and, like the native antigen, was found in the pellet fraction after high-speed centrifugation of bacterial extracts. The 19-kDa antigen in crude bacterial extracts, and the purified recombinant antigen, bound strongly to concanavalin A, indicating the possibility of posttranslational glycosylation. The recombinant antigen stimulated T-cell proliferation in vitro when added to assays either in the form of whole recombinant bacteria or as a purified protein. Homologous expression of mycobacterial antigens in a rapid-growing mycobacterial host may be particularly useful for the immunological characterization of proteins which are subject to posttranslational modification.