Kinetics and Thermodynamics of Virus Binding to Receptor.

Abstract

We have studied the kinetics and thermodynamics of a virus interacting with its receptor using human rhinovirus serotype 3 (HRV3), soluble intercellular adhesion molecule-1 (ICAM-1, CD54) containing Ig superfamily domains 1-5 (sICAM-1), and surface plasmon resonance. There were two classes of binding sites for sICAM-1 on HRV3, each comprising about 50% of the total sites, with association rate constants of 2450 {+/-} 300 and 134 {+/-} 11 M[IMG] s[IMG]. These rates are low, consistent with binding to a relatively inaccessible site in the rhinovirus canyon. By contrast, three monoclonal antibodies bound to sICAM-1 with a single rate constant of 17,000-48,000 M[IMG] s[IMG]. The dissociation rate constant for HRV3 was 1.7 {+/-} 0.1 [IMG] 10[IMG] s[IMG], giving calculated dissociation constants of 0.7 {+/-} 0.1 and 12.5 {+/-} 1.2 {micro}M. Agreement was good with saturation binding in solution, which showed two sites of similar abundance with K[IMG] of 0.55 {+/-} 0.2 and 5.7 {+/-} 2.0 {micro}M. A bivalent chimera of ICAM-1 with the IgA1 Fc region bound with K[IMG]= 50 and 410 nM, showing 17-fold enhanced affinity. Lowering pH from 8.0 to 6.0 reduced affinity by approximately 50-fold, primarily by reducing the on rate. Thermodynamic measurements showed that binding of ICAM-1 to HRV3 is endothermic, by contrast to binding to monoclonal antibody. The heat that is absorbed of 3.5 and 6.3 kcal/mol for the two classes of ICAM-1 binding sites may contribute to receptor-mediated disruption of virions, which has an activation energy of about 42 kcal/mol.