Tyrosine phosphatases (PTPs) constitute a family of closely related key regulatory enzymes that,in conjunction with protein-tyrosine kinases,control the state of tyrosine phosphorylation in a cellular context.M.tuberculosis has two phosphotyrosine phosphatases (PTPs),PtpA and PtpB,and has no tyrosine kinase genes annotated in its genome sequence database,suggesting that the targets of these two phosphatases may be present in the host cell,and involved in host-pathogen interactions.YossefAv-Gay,however,demonstrated the existence of a tyrosine kinase in M.tuberculosis,which phosphorylates PtpA (Bach et al.,2009).It was demonstrated that PtpA is secreted by M.tuberculosis in infected human macrophages,and it was also very elegantly demonstrated that VPS33B,a regulator of membrane fusion,is a PtpA substrate.Considered together,these data demonstrate that PtpA is essential for mycobacterial intracellular persistence,emerging as a promising target for therapeutic intervention.