Residues on Both Faces of the First Immunoglobulin Fold Contribute to Homophilic Binding Sites of PECAM-1/CD31*
- From the Imperial Cancer Research Fund Cell Adhesion Laboratory, Imperial Cancer Research Fund Laboratories, University of Oxford, Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and the ‡Laboratory of Molecular Biophysics and the Oxford Centre for Molecular Sciences, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
Abstract
CD31 (PECAM-1) is a member of the immunoglobulin superfamily whose extracellular domain is comprised of six immunoglobulin-like domains. It is widely expressed on endothelium, platelets, around 50% of lymphocytes, and cells of myeloid lineage. CD31 has been shown to be involved in interendothelial adhesion and leukocyte-endothelial interactions, particularly during transmigration. CD31-mediated adhesion is complex, because CD31 is capable of mediating both homophilic and multiple heterophilic adhesive interactions. Here we show that the NH2-terminal (membrane-distal) immunoglobulin domain of CD31 is necessary but not sufficient to support stable homophilic adhesion. Key residues forming the binding site within this domain have been identified by analysis of 26 single point mutations, representing the most systematic analysis of a fully homophilic interaction between immunoglobulin superfamily family members to date. This revealed five mutations that affect homophilic binding. Uniquely, the residues involved are exposed on both faces of the immunoglobulin fold, leading us to propose a novel mechanism for CD31 homophilic adhesion.
Footnotes
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↵* This work was supported by the Yamanouchi Research Institute (Ph.D. Studentship awarded to J. P. N.), the Wellcome Trust (Research Training Fellowship awarded to C. D. B. and Senior Research Fellowship awarded to D. L. S.), the Royal Society (Royal Society University Research Fellowship awarded to E. Y. J.), and the Imperial Cancer Research Fund (to J. P. N. and D. L. S.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ To whom correspondence should be addressed: Cell Adhesion Group, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford OX3 9DU, UK. Tel.: 44-1865-222355; Fax: 44-1865-222431; E-mail:dsimmons{at}molbiol.ox.ac.uk.
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↵1 The abbreviations used are: mAb, monoclonal antibody; ELISA, enzyme-linked immunosorbent assay; ICAM, intercellular adhesion molecule; LFA, leukocyte function associated antigen; GPI, glycosylphosphatidylinositol; VCAM, vascular cell adhesion molecule; PCR, polymerase chain reaction; PBS, phosphate-buffered saline.
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- Received March 4, 1997.
- Revision received May 5, 1997.
