Recent Topics of Titration Calorimetry 1. An Isothermal Titration Calorimetric Study of the Antigen-Antibody Interaction: The Affinity Maturation of Anti-4-Hydroxy-3-Nitrophenylacetyl Mouse Monoclonal Antibody.

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To understand the mechanism of affinity maturation, the antigen-antibody interactions between 4-hydroxy-3-nitrophenylacetyl caproic acid (NP-Cap) and the Fab fragments of three anti-4-hydroxy-3-nitrophenylacetyl (NP) antibodies, N1G9, 3B44, and 3B62, were examined by isothermal titration calorimetry. The analyses revealed that all of these interactions were mainly driven by negative changes in enthalpy. The enthalpy changes decreased linearly with temperature in the range of 25∼45°C, producing negative changes in heat capacity. On the basis of the dependency of binding constants on the sodium chloride concentration, it was shown that, during the affinity maturation of the anti-NP antibody, the electrostatic effect did not significantly contribute to the increase in the binding affinity. It was also found that, as the logarithm of the binding constants increased during the affinity maturation of the anti-NP antibody, the magnitudes of the corresponding enthalpy, heat capacity, and unitary entropy changes increased almost linearly. On the basis of this correlation, it is concluded that, during the affinity maturation of the anti-NP antibody, a better surface complementarity is attained in the specific complex to obtain a higher binding affinity.
日本熱測定学会の論文