BINDING-KINETICS OF AN ANTIBODY AGAINST HIV P24 CORE PROTEIN MEASUREDWITH REAL-TIME BIOMOLECULAR INTERACTION ANALYSIS SUGGEST A SLOW CONFORMATIONAL CHANGE IN ANTIGEN P24

The interaction between HIV core protein p24 and the murine monoclonal antibody CB-4/1 or its Fab fragment showed unusual kinetics. Recombin ant p24 was immobilised in a hydrophilic carboxymethyldextran matrix. At high concentration of CB-4/1 Fab the association of the antigen-ant ibody complex proceeds in two phases, while dissociation is mono-expon ential. The antigen has a 'memory', i.e. shortly after dissociation of Fab-antigen complex the fast association phase is enhanced. Biphasic association was also found in solution. Experiments suggest a reversib le change of binding properties in the epitope region with an overall time constant of about 100 s at room temperature. Intermediate steps w ith faster time constants must be involved. Slow conformational change s of p24 seem to be the most probable explanation. A simple model that provides a quantitative description of this process could not be foun d. Real-time analysis of antibody binding by surface plasmon resonance is a powerful method for studying such changes in the time domain of a few seconds to a few minutes.