ATTEMPTS TO DEFINE FUNCTIONAL DOMAINS OF GAP JUNCTION PROTEINS WITH SYNTHETIC PEPTIDES

To map the binding sites involved in channel formation, synthetic pept ides representing sequences of connexin32 were tested for their abilit y to inhibit cell-cell channel formation. Both large peptides represen ting most of the two presumed extracellular loops of connexin32 and sh orter peptides representing subsets of these larger peptides were foun d to inhibit cell-cell channel formation. The properties of the peptid e inhibition suggested that the binding site is complex, involving sev eral segments of both extracellular loops. One of the peptides (a 12-m er) did not inhibit but instead was found to form channels in membrane s. Both in oocyte membranes and in bilayers, the channels formed by th e peptide were asymmetrically voltage dependent. Their unit conductanc es ranged from 20 to 160 pS. These data are discussed in the form of a model in which the connexin sequence represented by the peptide is pa rt of a beta structure providing the lining of the channel pore.