Characterization of the major membrane protein of virulent Mycobacterium tuberculosis

A protein with a molecular mass of 19 kDa was isolated and purified from enriched membrane fractions of the virulent Erdman strain of Mycobacterium tuberculosis. The protein is different from another 19-kDa protein, a lipoprotein, that was recently described (D. B. Young and T. R. Garbe, Res. Microbiol. 142:55-65, 1991). The sequencing strategy applied to this major membrane protein employed four different endoproteinases and resulted in sufficient overlapping peptide sequences for assignment of the entire protein sequence. Electron spray ionization mass spectrometry demonstrated a measured mass of 16,100, deviating from the predicted mass by only 2.86 atomic mass units. The sequence of this protein is unique. However, some similarities with other low-molecular-weight heat shock proteins were observed. Immunoblotting indicated that this protein is highly expressed in the virulent strains of M. tuberculosis. Its application to sera from patients with pulmonary tuberculosis showed promise as a serodiagnostic tool.