Mutations at the 46th residue change properties of Cx50 gap junction channels

Xiaoling Tong, The University of Western Ontraio

Abstract

The interface of the first transmembrane domain and the first extracellular loop (TM1/E1 border) in several gap junction (GJ) channels is known to line a portion of the pore and plays an important role in determining GJ channel properties. By introduction of a charged residue into this domain of Cx50, the resultant mutant channels showed drastically altered unitary conductance (γ_j) and transjunctional voltage-dependent gating (V_j-gating). Specifically G46D and G46E increased the Cx50 γ_j from 201 to 256 and 293 pS, respectively and G46K channel showed a decreased γ_j of only 20 pS. Moreover, in single channel recordings of homotypic G46K and heterotypic Cx50/G46K channels, only loop gating transitions were observed, indicating an apparent loss of fast V_j-dependent gating transitions. The homology structural models indicate that the pore surface electrostatic potential at the TM1/E1 border is a dictating factor in determining efficiency of ion permeation and V_j-gating of Cx50 GJ channels.