title: Ultrastructure and function of dimeric, soluble intercellular adhesion molecule-1 (ICAM-1).
abstract: Previous studies have demonstrated dimerization of intercellular adhesion molecule-1 (ICAM-1) on the cell surface and suggested a role for immunoglobulin superfamily domain 5 and/or the transmembrane domain in mediating such dimerization. Crystallization studies suggest that domain 1 may also mediate dimerization. ICAM-1 binds through domain 1 to the I domain of the integrin alpha(L)beta(2) (lymphocyte function-associated antigen 1). Soluble C-terminally dimerized ICAM-1 was made by replacing the transmembrane and cytoplasmic domains with an alpha-helical coiled coil. Electron microscopy revealed C-terminal dimers that were straight, slightly bent, and sometimes U-shaped. A small number of apparently closed ring-like dimers and W-shaped tetramers were found. To capture ICAM-1 dimerized at the crystallographically defined dimer interface in domain 1, cysteines were introduced into this interface. Several of these mutations resulted in the formation of soluble disulfide-bonded ICAM-1 dimers (domain 1 dimers). Combining a domain 1 cysteine mutation with the C-terminal dimers (domain 1/C-terminal dimers) resulted in significant amounts of both closed ring-like dimers and W-shaped tetramers. Surface plasmon resonance studies showed that all of the dimeric forms of ICAM-1 (domain 1, C-terminal, and domain 1/C-terminal dimers) bound similarly to the integrin alpha(L)beta(2) I domain, with affinities approximately 1.5--3-fold greater than that of monomeric ICAM-1. These studies demonstrate that ICAM-1 can form at least three different topologies and that dimerization at domain 1 does not interfere with binding in domain 1 to alpha(L)beta(2).
authors.affiliation: Center for Blood Research and the Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: Jun
authors.forename: C V
authors.initials: CV
authors.lastname: Carman
authors.forename: S D
authors.initials: SD
authors.lastname: Redick
authors.forename: M
authors.initials: M
authors.lastname: Shimaoka
authors.forename: H P
authors.initials: HP
authors.lastname: Erickson
authors.forename: T A
authors.initials: TA
authors.lastname: Springer
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D018360:Crystallography, X-Ray; D003545:Cysteine; D018076:DNA, Complementary; D019281:Dimerization; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry / Q000502:physiology; D008854:Microscopy, Electron; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000648:ultrastructure; D020349:Surface Plasmon Resonance; D013499:Surface Properties; D014162:Transfection
chemical_list: D018076:DNA, Complementary; D016169:Lymphocyte Function-Associated Antigen-1; D011994:Recombinant Proteins; D018799:Intercellular Adhesion Molecule-1; D003545:Cysteine