SEQUENCE REQUIREMENTS FOR ASSOCIATION OF PROTEIN-TYROSINE-PHOSPHATASEPEP WITH THE SRC-HOMOLOGY-3 DOMAIN OF INHIBITORY TYROSINE PROTEIN-KINASE P50(CSK)

Previously, we reported that the inhibitory tyrosine protein kinase p5 0(csk) is physically associated with the protein-tyrosine phosphatase PEP in hematopoietic cells. This interaction was shown to involve the Src homology 3 (SH3) region of Csk and a proline-rich sequence of PEP termed P1 (SRRTDDEIPPPLPERTPESFIVVEE). In this report, we have attempt ed to understand the structural basis for the highly specific associat ion of these two molecules in vivo. Our studies revealed that the prol ine-rich core of the P1 region of PEP (PPPLPERT) was necessary but not sufficient for binding to p50(csk). Additional sequences located carb oxyl to this motif were also needed for binding to the Csk SH3 domain in vitro and in vivo. Further analyses revealed that two aliphatic res idues (isoleucine 625 and valine 626; PESFIVVEE) mere especially impor tant for this effect. In addition to clarifying the molecular basis fo r the selective ability of PEP to associate with Csk, these results co nstitute further evidence that sequences outside proline-rich cores di ctate the specificity of SH3 domain-mediated interactions in vivo.