Soluble oligomers and fibrillar deposits of amyloid beta (A beta) are key agents of Alzheimer's disease pathogenesis. However, the mechanism of amyloid aggregation and its interaction with live cells still remain unclear requiring the preparation of large amounts of pure and different A beta peptides. Here we describe an Escherichia coli expression system using a fusion protein to obtain either A beta(1-40) or A beta(1-42) by essentially the same procedure. The fusion protein uses a His-tagged intestinal fatty acid binding protein (IFABP) followed by a six-glycine linker and a Factor Xa cleavage site before the A beta. The advantages of this system are that the fusion protein can be expressed in large amounts, that the fusion partner, IFABP, has been well characterized in terms of folding, that A beta or mutated A beta peptides can be obtained without any extra residues attached to the N-terminus and that the system can be used to incorporate fluorine-labeled amino acids. The incorporation of fluori ne-labeled amino acids using auxotrophic strains is a useful NMR probe of side chain behavior. We obtain final yields of 4 and 3 mg/L of culture for A beta(1-40) and A beta(1-42), respectively. (C) 2009 Elsevier Inc. All rights reserved.