SEQUENCES SURROUNDING THE SRC-HOMOLOGY-3 DOMAIN OF PHOSPHOLIPASE C-GAMMA-1 INCREASE THE DOMAINS ASSOCIATION WITH CBL

SH3 domains are protein modules that interact with proline-rich polype ptide fragments. Cbl is an adapter-like protein known to interact with several SH3 domains, including the PLC gamma 1 SH3 domain and the Grb 2 amino terminal SH3 domain. Here we explore whether sequences surroun ding the PLC gamma 1 SH3 domain core sequence (aa.796-851) can affect the binding to Cbl, a target used as a prototypical ligand. Consistent with previous reports, our results demonstrated a weak binding of Cbl to GST fusion proteins that strictly encompass the structural core of the PLC gamma 1 SH3 domain but a high-avidity binding to the Grb2 ami no-terminal SH3 domain. Inclusion of amino acids immediately flanking the PLC gamma 1 SH3 core domain, however, substantially increased bind ing of Cbl to a level comparable to that of the Grb2 amino-terminal SH 3 domain. The interaction of this extended PLC gamma 1 SH3 domain fusi on protein with Cbl was shown to depend entirely upon the interaction of the domain with a proline-rich motif in Cbl, ruling out the possibi lity that amino acids adjacent to the core SH3 domain of PLC gamma 1 p rovide independent Cbl binding. These data suggest that sequences surr ounding the SH3 domain of PLC gamma 1 may contribute to or stabilize t he association of the domain with the target protein, thus increasing its binding efficiency. (C) 1998 Academic Press.