Mutations in the carboxyl-terminal domain of phospholipase C-β1 delineate the dimer interface and a potential Gαq interaction site

Abstract

The carboxyl-terminal domain of phospholipase C-β is required for its stimulation by Gαq and for its Gαq-specific GTPase-activating protein (GAP) activity. We subjected this domain to a combination of deletion and alanine/glycine scanning mutagenesis to detect mutations that would inhibit either responsiveness to Gq or Gq GAP activity. Most mutations that altered either response or GAP activity diminished both in parallel. Many of these mutations map at the interface at which the carboxyl-terminal domain was recently shown to form a dimer (Singer, A. U., et al. (2001) Nat. Struct. Biol., 9, 32-36). Most others clustered in an area that is a plausible Gαq binding site. In addition, one mutation that differentially inhibited GAP activity relative to responsiveness to Gαq mapped in this region at a location modeled to be in close contact with the switch II region of Gαq. This is the site at which RGS proteins are thought to exert their GAP activity. Last, a deletion mutation differentially inhibited the response of phospholipase C-β1 to Gαq without blocking GAP activity. Its location in the molecule suggests that moving the attachment point of the catalytic domain can disrupt its ability to be activated by Gαq.