A novel Mycobacterium bovis antigen was identified from an expression
library using sera from naturally infected cattle. The Escherichia col
i recombinant clone expressed a 27 kDa protein, named P27. A rabbit se
rum against the recombinant antigen recognized a protein of 27 kDa in
cellular extracts from M. bovis and M. tuberculosis. No protein was re
cognized in the culture supernatant. Sequence analysis indicated that
P27 has a molecular mass of 24 kDa, showing a characteristic signal se
quence for lipoprotein modification (a signal peptidase type II site).
The gene is identical to a gene identified in the M. tuberculosis gen
ome sequencing project. Cellular fractionation experiments suggested t
hat P27 is an integral membrane protein. The antigen was recognized by
individual sera and peripheral blood mononuclear cells (PBMC) from di
seased cattle. PCR experiments with specific primers directed to the P
27 structural gene indicated that it is only present in the M. tubercu
losis species complex. In conclusion, a novel immunogenic lipoprotein
in M. bovis/M. tuberculosis has been identified. The results presented
here and elsewhere suggest that mycobacterial lipoproteins should be
considered in the design of new recombinant vaccines and diagnostic me
thods.