A specific intermolecular association between the regulatory domains of a Tec family kinase

Interleukin-2 tyrosine kinase (Itk), is a T-cell specific tyrosine kinase o f the Tec family. We have examined a novel intermolecular interaction betwe en the SH3 and SH2 domains of Itk. In addition to the interaction between t he isolated domains, we have found that the dual SH3/SH2 domain-containing fragment of Itk self-associates in a specific manner in solution. Tec famil y members contain the SH3, SH2 and catalytic domains common to many kinase families but are distinguished by a unique amino-terminal sequence, which c ontains a proline-rich stretch. Previous work has identified an intramolecu lar regulatory association between the proline-rich region and the adjacent SH3 domain of Itk. The intermolecular interaction between the SH3 and SH2 domains of Itk that we describe provides a possible mechanism for displacem ent of this intramolecular regulatory sequence, a step that may be required for full Tec kinase activation. Additionally, localization of the interact ing surfaces on both the SH3 and SH2 domains by chemical shift mapping has provided information about the molecular details of this recognition event. The interaction involves the conserved aromatic binding pocket of the SH3 domain and a newly defined binding surface on the SH2 domain. The interacti ng residues on the SH2 domain do not conform to the consensus motif for an SH3 proline-rich ligand. Interestingly, we note a striking correlation betw een the SH2 residues that mediate this interaction and those residues that, when mutated in the Tec family member Btk, cause the hereditary immune dis order, X-linked agamaglobulinemia. (C) 2000 Academic Press.