Functional characterization of the phospholipase C activity of Rv3487c and its localization on the cell wall of Mycobacterium tuberculosis

摘要

Mycobacterium tuberculosis survives and persists for prolonged periods within its host in an asymptomatic, latent state and can reactivate years later if the host’s immune system weakens. The dormant bacilli synthesize and accumulate triacylglycerol, reputed to be an energy source during latency. Among the phospholipases, phospholipase C plays an important role in the pathogenesis. Mutations in a known phospholipase C, plcC, of M. tuberculosis attenuate its growth during the late phase of infection in mice. Hydrolysis of phospholipids by phospholipase C generates diacylglycerol, a well-known signalling molecule that participates in the activation of extracellular signal-regulated kinases (ERK) through protein kinase C leading to macrophage activation. In the present study, we show that M. tuberculosis possesses an additional cell wall-associated protein, Rv3487c, with phospholipase C activity. The recombinant Rv3487c hydrolyses the substrate phosphatidylcholine and generates diacylglycerol by removing the phosphocholine. Furthermore, Rv3487c is expressed during infection as it exhibits significant humoral immunoreactivity with sera from children with tuberculosis, but not with that from adult patients.