Structural organization of intercellular channels II. Amino terminal domain of the connexins: sequence, functional roles, and structure

Abstract

The amino terminal domain (NT) of the connexins consists of their first 22–23 amino acids. Site-directed mutagenesis studies have demonstrated that NT amino acids are determinants of gap junction channel properties including unitary conductance, permeability/selectivity, and gating in response to transjunctional voltage. The importance of this region has also been emphasized by the identification of multiple disease-associated connexin mutants affecting amino acid residues in the NT region. The first part of the NT is α-helical. The structure of the Cx26 gap junction channel shows that the NT α-helix localizes within the channel, and lines much of the wall of the pore. Interactions of the amino acid residues in the NT with those in the transmembrane helices may be critical for holding the channel open. The predicted sites of these interactions and the applicability of the Cx26 structure to the NT of other connexins are considered.

Structural studies of N-terminal mutants of Connexin 32 using 1H NMR spectroscopy

“…The NT plays an important role in the structure-function relation of connexin channels [11]. In channels formed by Cx26 and Cx32 the NT: 1) forms a portion of the large diameter aqueous pore by virtue of an open turn involving residues 11–15 that positions the first 10 residues into the channel pore [12–14], 2) contains at least a portion of the transjunctional (V j ) voltage sensor [15–17], 3) is an important determinant of conductance, charge selectivity, ionic rectification and permeation of both intercellular channels and undocked hemichannels formed by Cx32 [18,19].…”

A structural and functional comparison of gap junction channels composed of connexins and innexins

“…In connexins, the NT is 22-23 amino acids in length including a short a-helix. The NT likely folds into the pore, lining part of the conduction pathway, consistent with its involvement in permeability, conductance and Vj-gating (reviewed by Beyer et al, 2012). Innexins also appear to require an NT which also plays a role in Vj-gating and rectification (Marks and Skerrett, 2014).…”

A Conserved LIR Motif in Connexins Mediates Ubiquitin-Independent Binding to LC3/GABARAP Proteins

“…In silico analysis of the amino acid sequence of rat Cx43 through the iLIR webtool [18] revealed a potential LIR motif in the amino terminal of the protein with core residues corresponding to tryptophan 4 (W4) and leucine 7 (L7). Further analysis of the amino acid sequence of the human [1] and rat connexin families ( Figure S1) evidenced that these residues were strongly conserved within the family, being present in 17 of the 20 human connexins and 15 of the 17 rat connexins. Given these observations we proceeded to explore the interaction between several connexins of the alpha subfamily with LC3B.…”

“…In humans, twenty members form the connexin family, while at least seventeen members have been reported in rats. Based on sequence homology, connexin genes can be grouped into four classes, α, β, γ and δ [1]. Each connexin consists of four transmembrane regions, two extracellular loops and one intracellular loop, with both the amino and carboxyl terminals facing the cytosol.…”