Interaction between GABA(A) receptor beta subunits and the multifunctional protein gC1q-R.
gamma-Aminobutyric acid type A (GABA(A)) receptors were immunopurified from bovine brain using a monoclonal antibody directed against the alpha1 subunit. Of the several proteins that copurified, a 34-kDa protein was analyzed further. After enrichment and tryptic proteolysis, the resulting fragments were 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 interaction was estimated to be very high. Using the yeast two-hybrid system, various GABA(A) receptor subunit intracellular loop constructs were tested for an interaction with gC1q-R. All beta subunits, but not alpha 1 and gamma 2 subunits, were found to bind to gC1q-R. NH(2)- and COOH-terminally truncated beta 2 subunit loops were used to find the region responsible for the interaction with gC1q-R. A stretch of 15 amino acids containing 7 positively charged residues was identified (amino acids 399--413). This region contains residue Ser-410, which is a protein kinase substrate, and it is known that phosphorylation 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 modulation of the mature function.
Schaerer
M T
MT
Department of Pharmacology, University of Bern, CH-3010 Bern, Switzerland.
Kannenberg
K
K
Hunziker
P
P
Baumann
S W
SW
Sigel
E
E
D000818:Animals; D002417:Cattle; D006624:Hippocampus / Q000378:metabolism; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D010766:Phosphorylation; D051381:Rats; D020239:Receptor Cross-Talk; D011951:Receptors, Complement / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000378:metabolism*; D015398:Signal Transduction
C490195:C1qbp protein, rat; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011951:Receptors, Complement; D011963:Receptors, GABA-A; C032402:complement 1q receptor