An FT-IR study of the beta-amyloid conformation: standardization of aggregation grade.

The aggregation of beta-amyloid peptides is very important for their neurotoxic effect; standardization of the aggregation grade is necessary for biological experiments. Measurement of aggregation with physicochemical methods is a difficult task. The present work revealed that FT-IR can be used for studying the aggregation properties of beta-amyloid peptides and the effects of environmental variables (solvent, pH, ions, and temperature) on aggregation. In dimethyl sulfoxide or hexafluoroisopropanol, amyloid peptides are in a monomeric state; on dilution with phosphate buffer just before measurement is made, aggregation begins. A detailed two-dimensional FT-IR correlation spectroscopic study was made of the conformational transitions that occur during the aggregation of beta-amyloid peptides. Two processes (random/helix-to-beta-sheet and aggregation of beta-sheets) and multiple conformational states were observed before the most stable form was attained. beta-Amyloid peptides undergo decomposition in basic buffers containing Ca(2+); this process should be avoided during aging experiments. Copyright 1999 Academic Press.