DIFFERENTIAL INTERACTIONS OF THE C-TERMINUS AND THE CYTOPLASMIC-I-II LOOP OF NEURONAL CA2-PROTEIN-ALPHA AND BETA-GAMMA-SUBUNITS - II - EVIDENCE FOR DIRECT BINDING( CHANNELS WITH G)

The present study was designed to obtain evidence for direct interacti ons of G-protein alpha (G alpha) and beta gamma subunits (G beta gamma ) with N- (alpha(1B)) and P/Q-type (alpha(1A)) Ca2+ channels, using sy nthetic peptides and fusion proteins derived from loop 1 (cytoplasmic loop between repeat I and II) and the C terminus of these channels. Fo r N-type, prepulse facilitation as mediated by G beta gamma was impair ed when a synthetic loop 1 peptide was applied intracellulary. Recepto r agonist-induced inhibition of N-type as mediated by G alpha was also impaired by the loop 1 peptide but only when applied in combination w ith a C-terminal peptide. For P/Q-type channels, by contrast, the G al pha-mediated inhibition was diminished by application of a C-terminal peptide alone. Moreover, in vitro binding analysis for N- and P/Q-type channels revealed direct interaction of G alpha with C-terminal fusio n proteins as well as direct interaction of G beta gamma with loop 1 f usion proteins. These findings define loop 1 of N- and P/Q-type Ca2+ c hannels as an interaction site for G beta gamma and the C termini for G alpha.