Cloning and sequencing of the gene for α antigen from Mycobacterium avium and mapping of B-cell epitopes

The complete nucleotide sequence of α antigen secreted from Mycobacterium avium (A-α) was determined. The gene encodes 330 amino acids, including 40 amino acids for the signal peptide, followed by 290 amino acids for the mature protein with a molecular mass of 30,811 Da. This is the first sequence of A-α. Comparisons between A-α and α antigens of Mycobacterium leprae, Mycobacterium bovis BCG, and Mycobacterium kansasii showed highly homologous regions which suggested a conserved functional domain and two less-homologous regions. Serological analysis of recombinant A-α, expressed by a series of deletion constructs, indicated the possibility that A-α carries at least six B-cell epitopes. The three antigenic determinants were common to Mycobacterium tuberculosis, M. kansasii, and M. avium. The results also suggested the possibility that there are three species-specific epitopes.