Using transposon mutagenesis, a BCG library, was screened for differences in colony formation. One clone, BCG TN18D9, was identified which demonstrates a unique phenotypic growth pattern in culture. The gene was cloned and sequenced and shown to be a member of a Glycine-rich family of proteins recently identified from the sequencing of M. tuberculosis H37Rv. We have made a His-tagged construct and used Nickel-column chromatography to purify the 18D9 protein from an E. coli expression system. This protein is being used for structural and functional studies. The investigations demonstrate that expression of this protein in transfected cells inhibits expression of heterologous antigens suggesting that it may effet antigen presentation. A DNA-vaccine construct has also been made and mice have been immunized to study the immune response to this protein and for its ability to protect against challenge with virulent M. tb organisms. Further studies will focus on characterization of this novel antigen as a mycobacterial immunosuppression factor.
