BBMB Research Seminars

March 6
Lie Min
Iowa State University
“Tyrosine kinase substrate recognition in T cell signaling"

1414 Molecular Biology Buidling
4:10 p.m.

Abstract:
Interleukin-2-tyrosine kinase (Itk) is a tyrosine kinase that is implicated in the T cell signal transduction and cytoskeleton reorganization after T cell receptor (TCR) engagement.  During T cell signaling, Itk selectively phosphorylates a tyrosine within phospholipase Cg1 (PLCg1).  We find that the remote SH2 domain in the substrate is required to achieve efficient tyrosine phosphorylation by Itk and extend this observation to two other Tec family kinases, Btk and Tec.  Additionally, we detect a stable interaction between the substrate SH2 domains and the kinase domain of Itk, and find that addition of specific, exogenous SH2 domains to the in vitro kinase assay competes directly with substrate phosphorylation.  Based on these results, we show that the kinetic parameters of a generic peptide substrate of Itk are significantly improved by fusing the peptide substrate to the SH2 domain of PLCg1.  The binding surface on PLCg1 that mediates recognition by Itk highlights a non-classical binding activity of the well-studied Src homology 2 (SH2) domain providing evidence that SH2 domains participate in important interactions beyond recognition of phosphotyrosine.  We extend this substrate docking mechanism into the full-length PLCg1.  This work is the first characterization of a substrate docking mechanism for the Tec kinases and provides insight into the mechanism of Tec family kinases substrate recognition.  This work also provides evidence for a novel, phosphotyrosine-independent regulatory role for the ubiquitous SH2 domain.