The native structure of intercellular adhesion molecule-1 (ICAM-1) is a dimer. Correlation with binding to LFA-1.
In solution, intercellular adhesion molecule-1 (ICAM-1) exhibits extremely low affinity for its receptor, LFA-1, as direct binding to LFA-1 has not been reported. Furthermore, there are conflicting reports on the ability of ICAM-1 in solution to inhibit cell adhesion events. These differences could be due to the valency or an oligomeric native biochemical form of membrane-bound and soluble ICAM-1, which may correlate with its ability to bind to integrins. To test this, stimulated adenocarcinoma (A549) cells or HUVEC were labeled with 35S-methionine/cysteine and treated with a chemical cross-linker. A high m.w. form (200 kDa) of ICAM-1 but not ICAM-2 was specifically immunoprecipitated from cross-linked cell lysates and supernatants. Affinity purification of crosslinked supernatants revealed that the majority of ICAM-1 was dimeric as opposed to recombinant soluble ICAM-1, which contains a minor fraction of dimer. Gel filtration chromatography was used to isolate monomeric and dimer-rich fractions of recombinant soluble ICAM-1, and tested for direct binding to affinity-purified LFA-1. Dimer-rich fractions demonstrated an enhanced ability and estimated affinity, compared with monomeric protein, to bind to purified LFA-1. These data suggest that ICAM-1 exists in its native membrane-bound and shed form as a non-covalent dimer, and that dimerization directly correlates with enhanced binding to LFA-1.
Reilly
P L
PL
Department of Immunologic Disease, Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, CT 06877, USA.
Woska
J R
JR
Jeanfavre
D D
DD
McNally
E
E
Rothlein
R
R
Bormann
B J
BJ
D003432:Cross-Linking Reagents / Q000737:chemistry*; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D015394:Molecular Structure; D011994:Recombinant Proteins / Q000302:isolation & purification; D014407:Tumor Cells, Cultured
D003432:Cross-Linking Reagents; D016169:Lymphocyte Function-Associated Antigen-1; D011994:Recombinant Proteins; D018799:Intercellular Adhesion Molecule-1