Cs. Myung et Jc. Garrison, Role of C-terminal domains of the G protein beta subunit in the activationof effecters, P NAS US, 97(16), 2000, pp. 9311-9316
Citations number
31
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
The prenyl group on the G protein gamma subunit is an important determinant
of protein-protein interactions between the beta gamma dimer and its targe
ts, such as alpha subunits, receptors, and effectors. In an effort to ident
ify domains of the beta subunit important for the activation of effecters,
we have prepared two types of mutants, one set in the domain suggested to f
orm a hydrophobic prenyl-binding pocket for the gamma subunit's prenyl grou
p (prenyl pocket mutants) and the other set in a domain between Gly(306) an
d Gly(319) in the beta propeller, which undergoes a conformational change w
hen the dimer binds to phosducin (conformational change mutants). Recombina
nt baculoviruses for each set of mutants were prepared, and the nine mutant
beta subunits were overexpressed with either the gamma(2) subunit (modifie
d with geranylgeranyl) or the gamma(2-L71S) subunit (gamma(2) with altered
CAAX sequence and modified with farnesyl), The purified dimers were tested
for their ability to couple G alpha(i1) to the A1 adenosine receptor and to
activate phospholipase C-beta or type II adenylyl cyclase, All dimers cont
aining mutant beta subunits were indistinguishable from wild-type beta(1)ga
mma(2) or beta(1)gamma(2-L71S) in coupling the receptor to G alpha(i1). The
prenyl pocket mutants expressed with gamma(2) were 10-fold less potent in
activating phospholipase C-beta and adenylyl cyclase than beta(1)gamma(2) a
nd had similar activities to beta(1)gamma(2-L71S). The conformational chang
e mutants caused a 15- to 23-fold decrease in EC50 values for activation of
these two effecters. Overall, the results suggest that the sites in G beta
identified by these mutants are very important in the activation of effect
ors. Furthermore, the nature of the prenyl group on G gamma may play an imp
ortant role in the conformational change leading to the activity of G beta
gamma on effecters.