Phospholipase Cβ1b directly binds the SH3 domain of Shank3 for targeting and activation in cardiomyocytes

Phospholipase Cβ1b (PLCβ1b) is an atypical splice variant of PLCβ1 that has a C-terminal proline-rich sequence instead of the PDZ-interacting motif common to other PLCβ subtypes. PLCβ1b targets to the cardiomyocyte sarcolemma through an undefined association with the scaffolding protein Shank3. The C-terminal splice variant specific sequence of PLCβ1b bound to deletion mutants of Shank3 that included the SH3 domain, but not to constructs lacking this domain. Mutating proline residues in the extreme C-terminal region of PLCβ1b prevented the interaction between PLCβ1b and Shank3 resulting in reduced sarcolemmal localization and downstream signalling responses. We conclude that PLCβ1b activation and downstream signalling require the association of a previously unidentified C-terminal proline-rich motif with the SH3 domain of Shank3. PLCβ1b is the first confirmed protein ligand for the SH3 domain of Shank3.