Correlation between changes in buried surface area and affinity in an antigen-antibody complex.

M URRUTIA, EJ SUNDBERG, BC BRADEN, J ISERN, FP SCHWARZ, EL MALCHIODI AND RA MARIUZZA.

Punta del Este, Uruguay

Congreso; Vth Latin American Congress of immunology; 1999

Vth Latin American Congress of immunology.

Antigen-antibody complexes provide useful models for analyzing the thermodynamics of protein-protein association reactions. We have employed site-directed mutagenesis, X-ray crystallography, and isothermal titration calorimetry to investigate the role of hydrophobic interactions in stabilizing the complex between the Fv fragment of the anti-hen egg white lysozyme (HEL) antibody D1.3 and HEL. Crystal structures of six FvD1.3-HEL mutant complexes in which an interface tryptophan residue (V(L)W92) has been replaced by residues with smaller side chains (alanine, serine, valine, aspartate, histidine, and phenylalanine) were determined to resolutions between 1.75 and 2.00 A. In the wild-type complex, V(L)W92 occupies a large hydrophobic pocket on the surface of HEL and constitutes an energetic "hot spot" for antigen binding.