title: Analysis of four connexin26 mutant gap junctions and hemichannels reveals variations in hexamer stability.
abstract: Connexin26 is a ubiquitous gap junction protein that serves critical homeostatic functions. Four single-site mutations found in the transmembrane helices (M1-M4) cause different types of dysfunctional channels: 1), Cx26T135A in M3 produces a closed channel; 2), Cx26M34A in M1 severely decreases channel activity; 3), Cx26P87L in M2 has been implicated in defective channel gating; and 4), Cx26V84L in M2, a nonsyndromic deafness mutant, retains normal dye coupling and electrophysiological properties but is deficient in IP(3) transfer. These mutations do not affect Cx26 trafficking in mammalian cells, and make normal-appearing channels in baculovirus-infected Sf9 membranes when imaged by negative stain electron microscopy. Upon dodecylmaltoside solubilization of the membrane fraction, Cx26M34A and Cx26V84L are stable as hexamers or dodecamers, but Cx26T135A and Cx26P87L oligomers are not. This instability is also found in Cx26T135A and Cx26P87L hemichannels isolated from mammalian cells. In this work, coexpression of both wild-type Cx26 and Cx26P87L in Sf9 cells rescued P87L hexamer stability. Similarly, in paired Xenopus oocytes, coexpression with wild-type restored function. In contrast, the stability of Cx26T135A hemichannels could not be rescued by coexpression with WT. Thus, T135 and P87 residues are in positions that are important for oligomer stability and can affect gap junction gating.
authors.affiliation: National Center for Microscopy and Imaging Research, Center for Research in Biological Systems, University of California, San Diego, La Jolla, California, USA.
authors.forename: Cinzia
authors.initials: C
authors.lastname: Ambrosi
authors.forename: Daniela
authors.initials: D
authors.lastname: Boassa
authors.forename: Jennifer
authors.initials: J
authors.lastname: Pranskevich
authors.forename: Amy
authors.initials: A
authors.lastname: Smock
authors.forename: Atsunori
authors.initials: A
authors.lastname: Oshima
authors.forename: Ji
authors.initials: J
authors.lastname: Xu
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Nicholson
authors.forename: Gina E
authors.initials: GE
authors.lastname: Sosinsky
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000072259:Connexin 26; D017630:Connexins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D003902:Detergents / Q000737:chemistry; D017629:Gap Junctions / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D006878:Hydroxides / Q000378:metabolism; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D009154:Mutation; D017830:Octoxynol / Q000737:chemistry; D009865:Oocytes / Q000378:metabolism; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D051381:Rats; D012995:Solubility; D013912:Threonine / Q000378:metabolism; D014981:Xenopus
chemical_list: D017630:Connexins; D003902:Detergents; C000607045:GJB2 protein, Xenopus; C000607042:GJB2 protein, human; C000607044:Gjb2 protein, rat; D006878:Hydroxides; D050505:Mutant Proteins; D000072259:Connexin 26; D013912:Threonine; D017830:Octoxynol; C031356:hydroxide ion