Interaction of phosducin-like protein with G protein beta gamma snbunits

Phosducin-like protein (PhLP), a widely expressed ethanol-responsive gene (Miles, M. F., Barhite, S., Sganga, M., and Elliott, M. (1993) Proc, Natl, Acad. Sci, U. S. A. 90, 10831-10835), is a homologue of phosducin, a known major regulator of G beta gamma signaling in retina and pineal gland, However, although phosducin has a well characterized role in retinal phototransduction, function of the PhLP remains unclear, In this study we examine the ability of PhLP to bind G beta gamma dimer in vitro and in vivo, Using PhLP glutathione S-transferase fusion proteins, we show that PhLP directly binds G beta gamma in vitro, Studies with a series of truncated PhLP fusion proteins indicate independent binding of G beta gamma to both the amino- and C-terminal halves of PhLP. Protein-protein interactions between G beta gamma and PhLP are inhibited by the alpha subunit of G(o) and G(i3), suggesting that PhLP can bind only free G beta gamma, Finally, we show that PhLP complexes, at least partially, with G beta gamma in vivo, Following overexpression of epitope-tagged PhLP together with G beta(1) gamma(2) proteins in COS-7 cells, a PhLP-G beta gamma complex is co-immunoprecipitated by monoclonal antibody directed against the epitope tag, Similarly, polyclonal anti-PhLP antibody co-precipitates endogenous PhLP and G beta gamma proteins from NG108-15 cell lysates, These data are consistent with the hypothesis that PhLP is a widely expressed modulator of G beta gamma function. Furthermore, because alternate forms of the PhLP transcript are expressed, there may be functional implications for the existence of two G beta gamma-binding domains on PhLP.