INTERPRETING KINETIC RATE CONSTANTS FROM OPTICAL BIOSENSOR DATA RECORDED ON A DECAYING SURFACE

A capturing assay was used to monitor a Fab-antigen interaction using a BIACORE optical biosensor. The antigen, a truncated single-site muta nt (F43V) version of the CD4 receptor, was captured onto the sensor su rface using an immobilized nonneutralizing monoclonal antibody. While this assay design created an oriented antigen surface, the antigen slo wly dissociated during subsequent binding of the Fab, thus complicatin g the binding responses. In this paper, we illustrate how binding even ts occurring on a decaying surface can be accurately described by glob ally fitting the response data to a model that accounts for the backgr ound surface decay. Support for the method was obtained by showing the equilibrium dissociation constant calculated from the kinetic rate co nstants (K-d = 2.20 +/- 0.01 nM) was similar to the value measured in solution using titration calorimetry (K-d = 2.6 +/- 0.5 nM). The abili ty to interpret rate constants from decaying surfaces significantly ex tends the types of experimental systems that can be quantitatively stu died on optical biosensors. (C) 1998 Academic Press.