CLONING OF A BRUCELLA-MELITENSIS GROUP-3 ANTIGEN GENE ENCODING OMP28,A PROTEIN RECOGNIZED BY THE HUMORAL IMMUNE-RESPONSE DURING HUMAN BRUCELLOSIS

Brucella group 3 antigens (Ags) are outer membrane proteins (OMPs) wit h a molecular mass ranging from 25 to 30 kDa. The OMPs are of interest partially because of their potential use as vaccine and diagnostic re agents. We used human convalescent antibody (Ab) to clone a gene that encoded a 28-kDa protein from a lambda gt11 library of Brucella melite nsis 16M genomic DNA. DNA sequence analysis revealed a single open rea ding frame that would encode a protein of 26,552 Da. The 28-kDa protei n had a primary amino acid sequence that was 43% similar to a previous ly described Brucella abortus group 3 Ag, Omp25 (P. de Wergifosse, P. Lintermans, J. N. Limet, and A. Cloeckaert, J. Bacteriol. 177:1911-191 4, 1995). The similarity to a known group 3 OMP, immunoreactivity with Ab prepared against B. abortus group Ags, immunolabeling of whole cel ls, and Southern hybridization led to our conclusion that the B. melit ensis 28-kDa protein was a group 3 protein distinct from B. abortus Om p25. We designated the B. melitensis protein Omp28. Human convalescent sera from patients infected with B. abortus and Brucella suis as well as rabbit antisera prepared against killed B. abortus whole cells rec ognized B. melitensis Omp28 on Western blots (immunoblots). Furthermor e, mice and goats infected with smooth strains of B. melitensis produc ed Abs against Omp28. Our results may begin to explain the variability in molecular weight seen in Brucella group Ags and point toward their possible use in vaccination against infection as well as diagnosis of the disease.