Mt. Schaerer et al., Interaction between GABA(A) receptor beta subunits and the multifunctionalprotein gC1q-R, J BIOL CHEM, 276(28), 2001, pp. 26597-26604
gamma -Aminobutyric acid type A (GABA,) receptors were immunopurified from
bovine brain using a monoclonal antibody directed against the alpha1 subuni
t, Of the several proteins that copurified, a 34-kDa protein was analyzed f
urther. After enrichment and tryptic proteolysis, the resulting fragments w
ere sequenced, and the protein was identified as gC1q-R. Using anti-gC1q-R
and anti-GABA(A) receptor antibodies, mutual coimmunoprecipitation could be
demonstrated from solubilized rat brain membranes. The stability of this i
nteraction was estimated to be very high, Using the yeast two-hybrid system
, various GABAA receptor subunit intracellular loop constructs were tested
for an interaction with gC1q-R. All beta subunits, but not alpha1 and gamma
2 subunits, were found to bind to gC1q-R, NH2- and COOH-terminally truncate
d beta2 subunit loops were used to find the region responsible for the inte
raction with gC1q-R, A stretch of 15 amino acids containing 7 positively ch
arged residues was identified (amino acids 399-413), This region contains r
esidue Ser-410, which is a protein kinase substrate, and it is known that p
hosphorylation of this residue leads to an alteration in receptor activity.
Localization studies suggested a predominantly intracellular localization.
Our observations therefore suggest a tight interaction between gC1q-R and
the GABA(A) receptor which might be involved in receptor biosynthesis or mo
dulation of the mature function.