Genetic and immunological analysis of Mycobacterium tuberculosis fibronectin-binding proteins

Recombinant phage clones, TB1 and TB2, were selected from a Mycobacterium tuberculosis lambda gt11 DNA expression library by screening with a polyclonal antiserum raised against the antigen 85 complex of Mycobacterium bovis BCG. Analysis of recombinant DNA inserts and expressed fusion proteins showed that two new genes had been isolated. The product of clone TB2 was identified as a member of the 30/31-kDa antigen 85 complex. Restriction enzyme analysis showed that this gene differs from previously cloned members of this antigen complex, with detailed serological analysis indicating that it may encode the 85C component. Antisera raised against the expressed product of clone TB1 recognized a 55-kDa protein in M. tuberculosis extracts. The 55-kDa protein also has fibronectin-binding activity and, like the 30/31-kDa family, is a prominent target of the antibody response in patients with mycobacterial disease. Although the clones were selected by using the same antiserum, detailed analysis by serology and by DNA hybridization showed that they represent two quite distinct types of fibronectin-binding activities expressed by M. tuberculosis. Further analysis of the fibronectin-binding antigens of M. tuberculosis may provide important insights into their role in mediating the interaction with the host immune system.