MONOCLONAL-ANTIBODIES AGAINST THE ACETYLCHOLINE-RECEPTOR GAMMA-SUBUNIT AS SITE-SPECIFIC PROBES FOR RECEPTOR TYROSINE PHOSPHORYLATION

Tyrosine phosphorylation of the nicotinic acetylcholine receptor (AChR ) may be involved in AChR desensitization and clustering. Torpedo AChR gamma-subunit is phosphorylated at Tyr(365). Using overlapping synthe tic peptides, we have precisely mapped the epitopes of five anti-gamma -subunit monoclonal antibodies (mAbs) and found that the epitope(s) fo r the mAbs 154, 165 and 168 (gamma 365-370) all contain Tyr(365). mAb 168 is a known blocker of AChR channel function. Using peptide analogu es, Tyr(365) was found to be indispensable for mAb165 binding; further more its binding was selectively inhibited by in vitro AChR tyrosine p hosphorylation. The possible connection between gamma-subunit phosphor ylation and regulation of AChR function and the proven usefulness of t hese mAbs as tools should facilitate functional studies of AChR gamma- subunit phosphorylation.