The binding constant for amyloid Abeta40 peptide interaction with human serum albumin.

Human serum albumin (HSA) is the major carrier of Abeta peptides in blood plasma. 1:1 interaction stoichiometries were established in previous indirect antibody-based studies for both Abeta40 and Abeta42, but corresponding binding constants were not provided. In this study we applied direct titrations of HSA with Abeta40 monitored using circular dichroism spectroscopy and obtained a dissociation constant (K(d)) of 5+/-1 microM for a HSA complex with Abeta40. The interaction resulted in an increase of the alpha-helical contents in the complex, compared to its components, which is quantitatively consistent with the known ability of Abeta40 to adopt a partially alpha-helical conformation in a hydrophobic environment. The relevance of these findings for the role of HSA in Abeta physiology is discussed.