Global changes in amide hydrogen exchange rates for a protein antigen in complex with three different antibodies

Abstract

The binding of anti-lysozyme monoclonal antibodies, D44.1 or D1.3, to their antigen reduces the rate of exchange for many amide hydrogens in lysozyme. The D44.1 antibody contacts a similar region of lysozyme to the HyHEL-5 antibody, while the D1.3 antibody binds to the side of lysozyme which is opposite to the HyHEL-5 and D44.1 epitopes. We compare the effects of binding these antibodies on amide hydrogen exchange rates in lysozyme. These comparisons suggest that there are regions of lysozyme that fluctuate in a coordinated manner such that the effects of binding can be propagated to regions that are distant from the epitope. The activation enthalpies for hydrogen exchange for 36 of the 126 amide hydrogens in lysozyme and for 25 of 126 lysozyme amide hydrogens in the lysozyme-D1.3 complex are also reported. These data suggest that the reduction in amide hydrogen exchange rates upon antibody binding reflect changes in the dynamics of the antigen. These changes contribute to a reduction in the specific heat capacity upon binding.