CHARACTERIZATION OF A NOVEL MYCOBACTERIUM-BOVIS SECRETED ANTIGEN CONTAINING PGLTS REPEATS

Serum from naturally infected cattle was used to identify a novel Myco bacterium bovis antigen from an expression library. The first recombin ant product identified was a fusion protein with lacZ (55 kDa). A clon e containing the whole gene was also obtained. This clone expressed a 38-kDa protein. A rabbit serum against the recombinant antigen reacts in M. bovis supernatants with two proteins of 36 and 34 kDa. The new p rotein was called P36/P34. The gene cloned has a deduced amino acid se quence with a predicted molecular mass of 28 kDa, showing a characteri stic signal sequence for exportation. The protein bears partial homolo gy to a 28 kDa protein from M. leprae. An interesting feature of the P 36/P34 sequence is that it contains several PGLTS repeats, which are n ot present in the M. leprae protein. Antigenic determinants seem also to be conserved between the two proteins because sera from leprosy pat ients recognized the recombinant M. bovis protein. The discrepancy amo ng the molecular mass deduced from the sequence (28 kDa), that of the recombinant protein in Escherichia coli (38 kDa), and that of the nati ve protein in M. bovis (36 and 34 kDa) could be attributed to posttran slational modifications or to the high proline content that may alter the migration properties of the protein. This antigen seems to be immu nodominant during bovine tuberculosis, because 8 of 9 serum specimens from diseased cattle are reactive. The homology among the M. leprae 28 -kDa protein, the protein described in this article, and a recently de scribed M. tuberculosis protein suggests the existence of a new protei n family in mycobacteria.