| Abstract
| - Antibodies against β-amyloid peptides (Aβs) are considered an important therapeutic opportunity in Alzheimer'sdisease. Despite the vast interest in Aβ no thermodynamic data on the interaction of antibodies with Aβ areavailable as yet. In the present study we use isothermal titration calorimetry (ITC) and surface plasmonresonance to provide a quantitative thermodynamic analysis of the interaction between soluble monomericAβ(1−40) and mouse monoclonal antibodies (mAb). Using four different antibodies directed against theN-terminal, middle, and C-terminal Aβ epitopes, we measured the thermodynamic parameters for the bindingto Aβ. Each antibody species was found to have two independent and equal binding sites for Aβ with bindingconstants in the range of 107 to 108 M-1. The binding reaction was essentially enthalpy driven with a reactionenthalpy of Δ≈ −19 to −8 kcal/mol, indicating the formation of tight complexes. The loss inconformational freedom was supported by negative values for the reaction entropy Δ. We also measuredthe heat capacity change of the 1mAb:2Aβ reaction. Δwas large and negative but could not beexplained exclusively by the hydrophobic effect. The free energy of binding was found to be linearly correlatedwith the size of the epitope.
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