The SH3 domain of Bruton's tyrosine kinase interacts with Vav, Sam68 and EWS.

Bruton tyrosine kinase (BTK) is a cytoplasmic protein tyrosine kinase which controls crucial steps of differentiation of B lymphocytes. Mutations affecting either the PH, SH3, SH2 or kinase domain of BTK all give rise to X linked agammaglobulinaemia (XLA) in humans. In this study, the authors report that the BTK-SH3 domain binds to a set of proteins expressed in pro-B, pre-B and B cell lines. Three of them were characterized as Vav, Sam68 and EWS. The authors show that a Pro-->Leu substitution in a region of the SH3 domain, which is deleted in an XLA patient, is sufficient to abolish BTK-SH3 binding potential. The authors also report that several of the BTK-SH3 binding proteins, including Sam68, EWS and Vav, are tyrosine phosphorylated in conditions that also promote BTK kinase activity. For EWS and Sam68 this tyrosine phosphorylation was cell cycle dependent.