Activation of phospholipase C-γ1 (PLC-γ1), a critical early step in T cell activation through the T cell antigen receptor (TCR), is regulated by a complex of hematopoietic-specific adaptor proteins that includes SLP-76 (SH2 domain-containing leukocyte protein of 76 kD). P-I, a proline-rich 67-amino acid region of SLP-76 that binds to the SH3 domain of PLC-γ1 (SH3PLC), is required for TCR-mediated activation of PLC-γ1. Gonen et al. expressed deletion mutants of SLP-76 in an SLP-76-deficient cell line and discovered that, whereas complete deletion of P-I attenuated TCR-induced PLC-γ1 tyrosine phosphorylation and downstream sequelae of PLC-γ1 activation (calcium flux and NFAT activation), this did not depend on any particular portion of P-I. Further, SLP-76 functionality did not depend on its ability to bind SH3PLC. Indeed, a mutant in which the SH3PLC-binding region was deleted and the remaining amino acid sequence of P-I was scrambled to disrupt any other protein-binding domains retained the ability to mediate NFAT activation. Thus, the authors conclude that function of the P-I region may be independent of any protein-protein interactions and that this region may instead serve a structural role, perhaps as a spacer or a hinge.
R. Gonen, D. Beach, C. Ainey, D. Yablonski, T cell receptor-induced activation of phospholipase C-γ1 depends on a sequence-independent function of the P-I region of SLP-76. J. Biol. Chem. 280, 8364-8370 (2005). [Abstract] [Full Text]