title: Homophilic adhesion of human CEACAM1 involves N-terminal domain interactions: structural analysis of the binding site.
abstract: CEACAM1 on leukocytic, endothelial, and epithelial cells functions in homophilic adhesion, tumor suppression, regulating cell adhesion and proliferation, and in heterophilic adhesion as a receptor for E-selectin and Neisseria meningiditis, Neisseria gonorrhoeae, Haemophilus influenzae, and murine coronaviruses. The 8 transmembrane isoforms of human CEACAM1 possess an extracellular N-terminal IgV domain, followed by variable numbers of IgC2 domains. To establish which key amino acids contribute specifically to CEACAM1 homophilic adhesion, exposed amino acids in the N-terminal domain of a soluble form of CEACAM1 were subjected to mutagenesis. Analyses of mutant proteins with conformationally dependent antibodies indicated that most mutations did not substantially affect the structural integrity of CEACAM1. Nevertheless, decreased adhesion was observed for the single mutants V39A or D40A (single-letter amino acid codes) in the CC' loop and for the triple mutants located in the GFCC'C" face of the N-terminal domain. Interestingly, whereas single mutations in R64 or D82 that are predicted to form a salt bridge between the base of the D and F beta strands close to the critical V39 and D40 residues also abolish adhesion, an amino acid swap (R64D and D82R), which maintains the salt bridge was without significant effect. These studies indicate that the CC' loop plays a crucial role in the homophilic adhesion of CEACAM1. They further predict that specific hydrophobic amino acid residues on the nonglycosylated GFCC'C" face of CEACAM1 N-terminal domain are not only involved in heterophilic interactions with Opa proteins and H influenzae, but are also critical for protein-protein interactions between 2 CEACAM1 molecules on opposing cells.
authors.affiliation: Stem Cell Laboratory, National Blood Service, Nuffield Department of Clinical and Laboratory Sciences, and the MRC Molecular Haematology Unit, Institute of Molecular Medicine, Oxford, United Kingdom. swatt@molbio.ox.ac.uk
authors.forename: S M
authors.initials: SM
authors.lastname: Watt
authors.forename: A M
authors.initials: AM
authors.lastname: Teixeira
authors.forename: G Q
authors.initials: GQ
authors.lastname: Zhou
authors.forename: R
authors.initials: R
authors.lastname: Doyonnas
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: F
authors.initials: F
authors.lastname: Grunert
authors.forename: R S
authors.initials: RS
authors.lastname: Blumberg
authors.forename: M
authors.initials: M
authors.lastname: Kuroki
authors.forename: K M
authors.initials: KM
authors.lastname: Skubitz
authors.forename: P A
authors.initials: PA
authors.lastname: Bates
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D000943:Antigens, Differentiation / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D001665:Binding Sites; D016466:CHO Cells; D002272:Carcinoembryonic Antigen / Q000145:classification; D002448:Cell Adhesion / Q000502:physiology*; D015815:Cell Adhesion Molecules; D006224:Cricetinae; D003412:Cricetulus; D000939:Epitopes / Q000276:immunology; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D016297:Mutagenesis, Site-Directed; D009928:Organ Specificity; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000502:physiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; C069847:CD66 antigens; D002272:Carcinoembryonic Antigen; D015815:Cell Adhesion Molecules; D000939:Epitopes; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins