Affinity maturation increases the stability and plasticity of the Fv domain of anti-protein antibodies

ACIERNO, J. P., BRADEN, B. C., KLINKE, S., GOLDBAUM, F. A. AND CAUERHFF, A.

JOURNAL OF MOLECULAR BIOLOGY

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Año: 2007 vol. 374 p. 130 - 146

0022-2836

The somatic mutations accumulated in variable and framework regions ofantibodies produce structural changes that increase the affinity towards theantigen. This implies conformational and non covalent bonding changes atthe paratope, as well as possible quaternary structure changes andrearrangements at the VH?VL interface. The consequences of the affinitymaturation on the stability of the Fv domain were studied in a systemcomposed of two closely related antibodies, F10.6.6 and D44.1, whichrecognize the same hen egg-white lysozyme (HEL) epitope. The mAbF10.6.6 has an affinity constant 700 times higher than D44.1, due to a highersurface complementarity to HEL. The structure of the free form of the FabF10.6.6 presented here allows a comparative study of the conformationalchanges produced upon binding to antigen. By means of structuralcomparison, kinetics and thermodynamics of binding and stability studieson Fab and Fv fragments of both antibodies, we have determined that theaffinity maturation process of anti-protein antibodies affects the shape of thecombining site and the secondary structure content of the variable domain,stabilizes the VH?VL interaction, and consequently produces an increase ofthe Fv domain stability, improving the binding to antigen.