Complexes of the G protein subunit G beta(5) with the regulators of G protein signaling RGS7 and RGS9 - Characterization in native tissues and in transfected cells
Ds. Witherow et al., Complexes of the G protein subunit G beta(5) with the regulators of G protein signaling RGS7 and RGS9 - Characterization in native tissues and in transfected cells, J BIOL CHEM, 275(32), 2000, pp. 24872-24880
A novel protein class, termed regulators of G protein signaling (RGS), nega
tively regulates G protein pathways through a direct interaction with G alp
ha subunits and stimulation of GTP hydrolysis. An RGS subfamily including R
GS6, -7, -9, and -11, which contain a characteristic G gamma-like domain, a
lso has the unique ability to interact with the G protein beta subunit G be
ta(5). Here, we examined the behavior of G beta(5), RGS7, RGS9, and G alpha
in tissue extracts using immunoprecipitation and conventional chromatograp
hy. Native G beta(5) and RGS7 from brain, as well as photoreceptor-specific
G beta(5)L and RGS9, always co-purified as tightly associated dimers, and
neither RGS-free G beta(5) nor G beta(5)-free RGS could be detected, Co-exp
ression in COS-7 cells of GP, dramatically increased the protein level of R
GS7 and vice versa, indicating that cells maintain GP,:RGS stoichiometry in
a manner similar to GP gamma complexes. This mechanism is non-transcriptio
nal and is based on increased protein stability upon dimerization. Thus, an
alysis of native G beta(5)-RGS and their coupled expression argue that in v
ivo, G beta(5) and G gamma-like domain-containing RGSs only exist as hetero
dimers. Native G beta(5)-RGS7 did not co-precipitate or co-purify with G al
pha(o) or G alpha(q); nor did G beta(5)-L-RGS9 with G alpha(t). However, in
transfected cells, RGS7 and G beta(5)-RGS7 inhibited G alpha(q)-mediated C
a2+ response to muscarinic M3 receptor activation. Thus, G beta(5)-RGS dime
rs differ from other RGS proteins in that they do not bind to G alpha with
high affinity, but they can still inhibit G protein signaling.