Structure of the amino terminus of a gap junction protein

Charged amino acid residues in the amino terminus of gap junction forming p roteins (connexins) form part, if not all, of the transjunctional voltage s ensor of gap junction channels and play a fundamental role in ion permeatio n. Results from studies of the voltage dependence of N-terminal mutants pre dict that residues 1-10 of Group I connexins lie within the channel pore an d that the N-terminus forms the channel vestibule by the creation of a turn initiated by the conserved G12 residue. Here we report that intercellular channels containing mutations of G12 :in Cx32 to residues that are likely t o interfere with flexibility of this locus (G12S, G12Y, and G12V) do not ex press junctional currents, whereas a connexin containing a proline residue at G12 (Cx32G12P), which is expected to maintain a structure similar to tha t of the G12 locus, forms nearly wild-type channels. We have solved the str ucture of an N-terminal peptide of Cx26 (MD-WGTLQSILGGVNK) using H-1 2D NMR . The peptide contains two structured domains connected by a flexible hinge (domain-hinge-domain motif) that would allow the placement of the amino te rminus within the channel pore. Residues 1-10 adopt a helical conformation and line the channel entrance while residues 12-15 form an open turn. Overa ll, there is good agreement between the structural and dynamic features of the N-terminal peptide provided by MMR and the functional studies of the vo ltage dependence of channels formed by wild-type and N-terminal mutations, (C) Academic Press.