The Yersinia tyrosine phosphatase YopH targets a novel adhesion-regulated signalling complex in macrophages

Abstract

The Yersinia protein tyrosine phosphatase (PTP) YopH is translocated into eukaryotic cells by a type III secretion system that requires bacterial–host cell contact. YopH is composed of two modular effector domains: a substrate‐binding domain located in the N‐terminal region (residues 1–130) and a PTP catalytic domain located in the C‐terminal region (residues 206–468). Previous studies have shown that YopH selectively targets tyrosine‐phosphorylated proteins of approximate molecular weight 120 kDa (p120) and 55 kDa (p55) in murine macrophages. It has been demonstrated that p120 actually represents two tyrosine‐phosphorylated target proteins, Cas and Fyb. We used the substrate‐binding domain of YopH to affinity purify tyrosine‐phosphorylated target proteins from lysates of J774A.1 macrophages. Protein microsequencing identified p55 as murine SKAP‐HOM. Direct interaction between SKAP‐HOM and a catalytically inactive form of YopH was demonstrated in vitro and in macrophages. In addition, we obtained evidence that SKAP‐HOM is tyrosine phosphorylated in response to macrophage cell adhesion and that it forms a signalling complex with Fyb. We suggest that dephosphorylation of SKAP‐HOM and Fyb by YopH allows yersiniae to interfere with a novel adhesion‐regulated signal transduction pathway in macrophages.