title: A fully atomistic model of the Cx32 connexon.
abstract: Connexins are plasma membrane proteins that associate in hexameric complexes to form channels named connexons. Two connexons in neighboring cells may dock to form a "gap junction" channel, i.e. an intercellular conduit that permits the direct exchange of solutes between the cytoplasm of adjacent cells and thus mediate cell-cell ion and metabolic signaling. The lack of high resolution data for connexon structures has hampered so far the study of the structure-function relationships that link molecular effects of disease-causing mutations with their observed phenotypes. Here we present a combination of modeling techniques and molecular dynamics (MD) to infer side chain positions starting from low resolution structures containing only C alpha atoms. We validated this procedure on the structure of the KcsA potassium channel, which is solved at atomic resolution. We then produced a fully atomistic model of a homotypic Cx32 connexon starting from a published model of the C alpha carbons arrangement for the connexin transmembrane helices, to which we added extracellular and cytoplasmic loops. To achieve structural relaxation within a realistic environment, we used MD simulations inserted in an explicit solvent-membrane context and we subsequently checked predictions of putative side chain positions and interactions in the Cx32 connexon against a vast body of experimental reports. Our results provide new mechanistic insights into the effects of numerous spontaneous mutations and their implication in connexin-related pathologies. This model constitutes a step forward towards a structurally detailed description of the gap junction architecture and provides a structural platform to plan new biochemical and biophysical experiments aimed at elucidating the structure of connexin channels and hemichannels.
authors.affiliation: Institut Pasteur of Montevideo, Montevideo, Uruguay. spantano@pasteur.edu.uy
authors.forename: Sergio
authors.initials: S
authors.lastname: Pantano
authors.forename: Francesco
authors.initials: F
authors.lastname: Zonta
authors.forename: Fabio
authors.initials: F
authors.lastname: Mammano
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry; D002244:Carbon / Q000737:chemistry; D002462:Cell Membrane / Q000378:metabolism; D017630:Connexins / Q000737:chemistry* / Q000378:metabolism; D017629:Gap Junctions; D051379:Mice; D008854:Microscopy, Electron / Q000379:methods; D008968:Molecular Conformation; D009154:Mutation; D010641:Phenotype; D015221:Potassium Channels / Q000737:chemistry; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013302:Streptomyces / Q000378:metabolism; D000097002:Gap Junction beta-1 Protein
chemical_list: D001426:Bacterial Proteins; D002244:Carbon; D017630:Connexins; D015221:Potassium Channels; D000097002:Gap Junction beta-1 Protein; C107790:prokaryotic potassium channel