G protein βγ subunits bind to and inhibit the function of multiple Qa- and Qb,c-SNARE isoforms.

Abstract

While the ability of G protein {beta}{gamma} subunits (G{beta}{gamma}) to bind to and functionally inhibit the neuronal SNARE proteins Stx1A, SNAP25, and synaptobrevin in the presence of the calcium sensor synaptotagmin I is well documented, these three SNARE proteins, which form the core SNARE complex for synchronous evoked release in neurons, are but a subset of the larger family of SNARE proteins, which participate in many other exocytic processes within the cell and in other populations of secretory cells throughout the body, from which the release of neurotransmitters, hormones, and other factors is regulated by Gi/o-coupled GPCRs. The ability of G{beta}{gamma} to regulate these processes is unknown. To investigate the feasibility of this mechanism to inhibit SNARE function more broadly, we utilized a series of biochemical assays of binding and function with four Qa-SNAREs (Stx1A, Stx2, Stx3, and Stx4) and four Qb,c-SNAREs (SNAP25, SNAP23, SNAP29, and SNAP47) in tandem with the R-SNARE synaptobrevin, synaptotagmin I, and G{beta}{gamma}. G{beta}{gamma} was found to bind to multiple Qa-SNARE isoforms as well as SNAP23, and inhibit the lipid mixing function of these SNAREs, as well as SNAP29. Together, this data suggests a more broad role for the G{beta}{gamma}-SNARE pathway in the regulation of exocytosis beyond cells that express Stx1A or SNAP25.