YopH is a plasmid-encoded protein tyrosine phosphatase (PTPase) secreted by pathogenic Yersinia. Although the enzyme likely acts to dephosphorylate eukaryotic proteins during Yersinia infection of the mammalian host, the targets of YopH have not been identified. We infected the murine macrophage-like cell line J774A.1 with Yersinia pseudotuberculosis and investigated the specificity of YopH and YopHC403A, a catalytically inactive mutant derivative, for eukaryotic phosphoproteins. Upon infection, YopH specifically and rapidly dephosphorylated a macrophage protein of 120 kD. The 120-kD protein and a previously detected 55-kD substrate of YopH coprecipitated with YopHC403A. Coprecipitation of these proteins required tyrosine phosphorylation and could be competitively inhibited with excess phosphotyrosine. The 120- and 55-kD proteins that coprecipitate with YopHC403A exhibited the in vitro activity of protein tyrosine kinases (PTKases), suggesting that YopH dephosphorylates activated tyrosine kinases in vivo.

This content is only available as a PDF.