title: Convergence of experimental, computational and evolutionary approaches predicts the presence of a tetrameric form for CD3-zeta.
abstract: Experimental results using multiple site-specific infrared dichroism have shown that, when reconstituted into lipid bilayers, the orientation of the transmembrane domain of CD3-zeta is not compatible with a dimeric right-handed model reported previously. This model, obtained using a computational approach that uses evolutionary data, is in agreement with mutagenesis data and homology modelling. This suggested that, in our experimental conditions, the oligomeric state of CD3-zeta may not be dimeric. We have explored this possibility by performing global searching molecular dynamics simulations assuming different homo-oligomeric sizes (from 2 to 6). In these simulations, the helix tilt was restrained to the average helix tilt obtained experimentally, 12 degrees. Only a left-handed tetrameric model was compatible with the experimentally observed tilt and rotational orientation of the helix, and was also the lowest-energy model amongst the candidate structures obtained. Furthermore, simulations performed using close homologues demonstrate that this model is compatible with evolutionary conservation data. Finally, the pattern of residue conservation in the zeta family of proteins strongly argues in favour of the presence of a left-handed hetero-oligomer with an orientation compatible with the tetramer we present. These results show that both the known dimeric and the so far undetected tetrameric form may be of functional importance in the cell.
authors.affiliation: Cambridge Centre for Molecular Recognition, Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK.
authors.forename: Jaume
authors.initials: J
authors.lastname: Torres
authors.forename: John A G
authors.initials: JA
authors.lastname: Briggs
authors.forename: Isaiah T
authors.initials: IT
authors.lastname: Arkin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017252:CD3 Complex / Q000737:chemistry* / Q000378:metabolism*; D003198:Computer Simulation; D017124:Conserved Sequence; D019281:Dimerization; D019143:Evolution, Molecular; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017385:Sequence Homology; D013816:Thermodynamics
chemical_list: D017252:CD3 Complex; C121704:CD3 antigen, zeta chain; D008051:Lipid Bilayers