title: Complete predicted three-dimensional structure of the facilitator transmembrane protein and hepatitis C virus receptor CD81: conserved and variable structural domains in the tetraspanin superfamily.
abstract: Tetraspanins are a superfamily of transmembrane proteins implicated in cellular development, motility, and activation through their interactions with a large range of proteins and with specific membrane microdomains. The complete three-dimensional structure of the tetraspanin CD81 has been predicted by molecular modeling and from the crystallographic structure of the EC2 large extracellular domain. Periodicity of sequence conservation, homology modeling, secondary structure prediction, and protein docking were used. The transmembrane domain appears organized as a four-stranded left-handed coiled coil directly connecting to two helices of the EC2. A smaller extracellular loop EC1 contains a small largely hydrophobic beta-strand that packs in a conserved hydrophobic groove of the EC2. The palmitoylable intracellular N-terminal segment forms an amphipathic membrane-parallel helix. Structural variability occurs mainly in an hypervariable subdomain of the EC2 and in intracellular regions. Therefore, the variable interaction selectivity of tetraspanins originates both from sequence variability within structurally conserved domains and from the occurrence of small structurally variable domains. In CD81 and other tetraspanins, the numerous membrane-exposed aromatic residues are asymmetrically clustered and protrude on one side of the transmembrane domain. This may represent a functional specialization of these two sides for interactions with cholesterol, proteins, or membrane microdomains.
authors.affiliation: Institut Cochin, INSERM U567, CNRS UMR 8104, Université Paris V, Département de Biologie Cellulaire, 75014 Paris, France. seigneuret@cochin.inserm.fr
authors.forename: Michel
authors.initials: M
authors.lastname: Seigneuret
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000737:chemistry*; D002462:Cell Membrane / Q000378:metabolism; D002784:Cholesterol / Q000737:chemistry; D017124:Conserved Sequence; D016174:Hepacivirus / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008024:Ligands; D021962:Membrane Microdomains / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012984:Software; D060225:Tetraspanin 28
chemical_list: D015703:Antigens, CD; C554798:CD81 protein, human; D008024:Ligands; D008565:Membrane Proteins; D060225:Tetraspanin 28; D002784:Cholesterol