Variations in Antigen−Antibody Association Kinetics as a Function of pH and Salt Concentration:  A QSAR and Molecular Modeling Study

• Published in: Biochemistry (Easton) 2005-11, Vol.44 (44), p.14409-14418
• Main Authors: Dejaegere, Annick, Choulier, Laurence, Lafont, Virginie, De Genst, Erwin, Altschuh, Danièle
• Format: Article
• Language: English
• Subjects: Animals; Antibodies - chemistry; Antibodies - genetics; Antibodies - metabolism; Antigen-Antibody Complex - chemistry; Antigens - chemistry; Antigens - genetics; Antigens - metabolism; Hydrogen-Ion Concentration; Models, Molecular; Multivariate Analysis; Muramidase - chemistry; Muramidase - genetics; Muramidase - metabolism; Protein Binding; Quantitative Structure-Activity Relationship; Salts - chemistry; Temperature
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi050986v

The relationship between three environmental factors (ionic strength, pH, and temperature) and antigen−antibody binding kinetics was investigated using QSAR (quantitative structure−activity relationship) and molecular modeling approaches. The interaction used for this analysis is that between the camel antibody fragment cAbLys3 and lysozyme. Binding kinetics were measured using a Biacore 2000 instrument, at NaCl concentrations between 50 and 500 mM, at pH's between 5 and 10, and at temperatures between 15 and 30 °C, according to multivariate experimental designs. Variations in kinetic on- and off-rate parameters were up to 400- and 16-fold, respectively. Mathematical models that relate log k on to experimental conditions were developed. They indicated an influence of all three factors, with a clear dependency between pH and NaCl concentration for their effect on k on. These models were able to predict on-rate parameters under new experimental conditions. Titration calculations using continuum electrostatics were performed on the crystallographic structures of the isolated and bound proteins to gain structural insight for the on-rate enhancement observed at pH