Structural and kinetic studies on two anti-lysozyme monoclonal antibodies raised against the same epitope. (Poster)

JUAN P. ACIERNO; SEBASTIÁN KLINKE; BRADFORD C. BRADEN; FERNANDO A.GOLDBAUM; ANA CAUERHFF

Bariloche, Pcia. de Río Negro, Argentina.

Congreso; XXXIX Reunión anual de SAIB (Sociedad Argentina de Investigación en Bioquímica y Biología Molecular) y SAB (Sociedad Argentina de Biofísica), Bariloche Protein Symposium.; 2003

SAIB y SAB

The Affinity maturation of anti-protein antibodies has been reported to be the result of small structural changes product of somatic hypermutation, mostly confined to the periphery of the antigencombining site. However, little is understood about how these small structural changes account for the increase in the affinity towards the antigen. Monoclonal antibody F10.6.6 was obtained from a long-term exposure to the antigen lysozyme, whereas mAb D44.1 is the result of short-term exposure to the same antigen. These mAbs are the result of identical or nearly identical somatic recombination events. Nevertheless, different framework and variable region mutations from germline genes result in an approximately 103 higher affinity for the F10.6.6 antibody. The crystallographic three-dimensional structures of both free and complexed Fab F10.6.6 were solved by molecular replacement at a resolution of 2.0 Å, using D44.1 structure as template. The interaction area, the amount and distance of contacts and the number of the interface waters are increased in the F10.6.6 complex in contrast to D44.1. Biosensor assays were performed in solvent stress conditions to identify the role of the structural waters present at the antigen-antibody interface. Affinity maturation produces a fine-tuning of the complementarity of the paratope towards the epitope, explaining how the immune system is able to increase the affinity of an anti-protein antibody.