Structure-based epitope mapping of Mycobacterium tuberculosis secretary antigen MTC28

Abstract Secretary proteins of Mycobacterium tuberculosis are the key players of mycobacterial infection pathway. MTC28 is a 28kDa proline-rich secretary antigen of Mycobacterium tuberculosis and is only conserved in pathogenic strains of mycobacteria. Here we report the crystal structure of MTC28 at 2.8 and 2.15 angstrom resolutions for structure based epitope design. MTC28 shares a mog1p fold consisting of seven antiparallel beta strands stacked between alpha helices. Five probable epitopes have been located on a solvent accessible flexible region by computational analysis of the structure of MTC28. Simultaneously, the protein is digested with trypsin and the resulting fragments are purified by HPLC. Such 10 purified peptide fragments are screened against sera from patients infected with pulmonary tuberculosis (PTB). Two out of these ten fragments namely128ALDITLPMPPR137 and 138WTQVPDPNVPDAFVVIADR157 are found to be major immunogenic epitopes that are localized on the outer surface of the protein molecule and are part of a single continuous epitope that have been predicted in silico. Mutagenesis and antibody inhibition studies are in accordance with the results obtained from epitope mapping.