title: Signaling lymphocytic activation molecule (CDw150) is homophilic but self-associates with very low affinity.
abstract: Signaling lymphocytic activating molecule ((SLAM) CDw150) is a glycoprotein that belongs to the CD2 subset of the immunoglobulin superfamily and is expressed on the surface of activated T- and B-cells. It has been proposed that SLAM is homophilic and required for bidirectional signaling during T- and B-cell activation. Previous work has suggested that the affinity of SLAM self-association might be unusually high, undermining the concept that protein interactions mediating transient cell-cell contacts, such as those involving leukocytes, have to be weak in order that such contacts are readily reversible. Using surface plasmon resonance-based methods and analytical ultracentrifugation (AUC), we confirm that SLAM is homophilic. However, we also establish a new theoretical treatment of surface plasmon resonance-derived homophilic binding data, which indicates that SLAM-SLAM interactions (solution K(d) approximately 200 micrometer) are in fact considerably weaker than most other well characterized protein-protein interactions at the cell surface (solution K(d) approximately 0.4-20 micrometer), a conclusion that is supported by the AUC analysis. Whereas further analysis of the AUC data imply that SLAM could form "head to head" dimers spanning adjacent cells, the very low affinity raises important questions regarding the physiological role and/or properties of such interactions.
authors.affiliation: Sir William Dunn School of Pathology, The University of Oxford, Oxford OX1 3RE, United Kingdom.
authors.forename: N
authors.initials: N
authors.lastname: Mavaddat
authors.forename: D W
authors.initials: DW
authors.lastname: Mason
authors.forename: P D
authors.initials: PD
authors.lastname: Atkinson
authors.forename: E J
authors.initials: EJ
authors.lastname: Evans
authors.forename: R J
authors.initials: RJ
authors.lastname: Gilbert
authors.forename: D I
authors.initials: DI
authors.lastname: Stuart
authors.forename: J A
authors.initials: JA
authors.lastname: Fennelly
authors.forename: A N
authors.initials: AN
authors.lastname: Barclay
authors.forename: S J
authors.initials: SJ
authors.lastname: Davis
authors.forename: M H
authors.initials: MH
authors.lastname: Brown
mesh_terms: D000818:Animals; D015703:Antigens, CD; D001402:B-Lymphocytes / Q000276:immunology; D002461:Cell Line, Transformed; D019281:Dimerization; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1 / Q000276:immunology; D006801:Humans; D007136:Immunoglobulins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008213:Lymphocyte Activation; D008958:Models, Molecular; D008962:Models, Theoretical; D011487:Protein Conformation; D051381:Rats; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins / Q000276:immunology; D000071177:Signaling Lymphocytic Activation Molecule Family Member 1; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D015703:Antigens, CD; D006023:Glycoproteins; D007136:Immunoglobulins; D011948:Receptors, Antigen, T-Cell; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; D000071177:Signaling Lymphocytic Activation Molecule Family Member 1