Functional Studies of Truncated Soluble Intercellular Adhesion Molecule 1 Expressed in Escherichia Coli

We have expressed in Escherichia coli the two N-terminal immunoglobulin (Ig)-like domains of the intercellular adhesion molecule 1 (ICAM-1). The first 188 residues of ICAM-1 were expressed with an N-terminal methionine (MP188) or as a maltose-binding fusion protein which was cleaved with factor Xa (XP188). After refolding, both MP188 and XP188 were active in binding to the leukocyte integrin lymphocyte function-associated antigen 1, which has previously been shown to bind to the N-terminal Ig domain of ICAM-1. The major group of rhinoviruses and malaria-infected erythrocytes bind to distinct sites within the first Ig-like domain of ICAM-1. Both MP188 and XP188 bound to malaria-infected erythrocytes; however, only XP188 inhibited human rhinovirus plaque formation. A product (MdQ1P188) with the initiation methionine fused to residue 2, i.e., with glutamine 1 deleted, inhibited plaque formation. MdQ1P188 was able to induce a conformational change of the virus capsid as shown by conversion of 149S particles to 85S particles, whereas MP188 had no effect. These results show that functionally active fragments of ICAM-1 can be produced in E. coli, that glycosylation is not required for ligand binding, and that the N-terminal residue of ICAM-1 is proximal to or part of the human rhinovirus-binding site.