PHOSPHORYLATION OF THE GABA(A) RECEPTOR BY CAMP-DEPENDENT PROTEIN-KINASE AND BY PROTEIN-KINASE-C - ANALYSIS OF THE SUBSTRATE DOMAIN

Previous work has shown that the GABA(A)-receptor (GABA(A)-R) could be phosphorylated by cAMP-dependent protein kinase (PKA), protein kinase C (PKC), and a receptor associated kinase. However, no clear picture has yet emerged concerning the particular subunit\subtypes of the GABA(A)-R that were phosphorylated by PKA and PKC. In the present report we show that an antibody raised against a 23 amino acid polypeptide corresponding to a sequence in the putative intracellular loop of the beta1 subunit of the receptor blocks the in vitro phosphorylation of the purified receptor by PKA and PKC. Moreover, N-terminal sequence analysis of the principal phosphopeptide fragment obtained after proteolysis of the receptor yielded a sequence that corresponds to the beta3 subunit of the receptor. Such data provide additional support for our hypothesis (Browning et al., 1990, Proc. Natl. Acad. Sci. USA 87:1315-1317) that both PKA and PKC phosphorylate the beta-subunit of the GABA(A)-R.