Surface plasmon resonance and nuclear magnetic resonance studies of ABAD-Aβ interaction

A beta binding alcohol dehydrogenase (ABAD) is an NAD-dependent mitochondrial dehydrogenase. The binding between ABAD and A beta is likely a direct link between A beta and mitochondrial toxicity in Alzheimer's disease. In this study, surface plasmon resonance (SPR) was employed to determine the temperature dependence of the affinity of the ABAD-A beta interaction. A van't Hoff analysis revealed that the ABAD-A beta association is driven by a favorable entropic change (Delta S = 300 +/- 30 J mol(-1) K-1) which overcomes an unfavorable enthalpy change (Delta H = 49 +/- 7 kJ/mol). Therefore, hydrophobic interactions and changes in protein dynamics are the dominant driving forces of the ABAD-A beta interaction. This is the first dissection of the entropic and enthalpic contribution to the energetics of a protein-protein interaction involving A beta. SPR confirmed the conformational changes in the ABAD-A beta complex after A beta binding, consistent with differences seen in the crystal structures of free ABAD and the ABAD-A beta complex. Saturation transfer difference (STD) NMR experiments directly and unambiguously demonstrated the inhibitory effect of A beta on the ABAD-NAD interaction. Conversely, NAD inhibits the A beta-ABAD interaction. Binding of A beta and binding of NAD to ABAD are likely mutually exclusive. Thus, A beta binding induces conformational and subsequently functional changes in ABAD, which may have a role in the mechanism of A beta toxicity in Alzheimer's disease.