Role of lsp a gene in the biology and pathogenesis of mycobacterium tuberculosis

Abstract

In Mycobacterium tuberculosis, there is only a single gene (Rv1539) that encodes for LspA (Signal peptidase) protein. There are more than 104 lipoproteins in M. tuberculosis that are matured by signal peptidase activity of LspA. Many of these lipoproteins have been reported as virulence factors for M. tuberculosis. Therefore the lspA gene turns out to be very attractive target to develop newer therapeutics to combat tuberculosis. In an attempt to understand the role of lspA gene in the biology and pathogenesis of M .tuberculosis, the lspAgene was cloned in a suitable vector and the protein was expressed and purified to raise polyclonal antibody in rabbit. The lspA gene was also overexpressed in M. tuberculosis H37Rv (M.tb:lspAand#8593;).Overexpression of lspA gene enhanced the in-vitro growth of M. tuberculosis. Electron microscopy showed enhanced thickness of M.tb:lspAand#8593;strain. Immunogoldexperiments demonstrate accumulation of LspA coated particles along the cell wall of strain. Furtherwork demonstrates enhanced resistance to first line antitubercular drugs too. By using aerosol route of infection and mouse model it has been shown here that the overexpression of the gene (lspA) makes the M. tuberculosisstrain more pathogenic and induces a strong immunogenic effect that leads to Th1 type of immune response. Furthermore, in silico analysis revealed that the lspAgene is a constitutively expressed gene that lies in an operon with Rv1540. This observation has been experimentally confirmed here. It has also been demonstrated here that the lspA gene is constitutively expressed and regulated by a strong promoter. Taken together the present study establishes the biological relevance of the lspA gene on a firm footing. We propose this may prove to be a good drug target to combat tuberculosis in the years to come.