Stereospecific amyloid-like fibril formation by a peptide fragment of β2-microglobulin

Understanding the role of the L/D-Stereospecificity of amino acids is important in obtaining further insight into the mechanism of the formation of amyloid fibrils. beta(2)-Microglobulin is a major component of amyloid fibrils deposited in patients with dialysis-related amyloidosis. A 22-residue peptide of beta(2)-Microglobulin, Ser20-Lys41 (L-K3 peptide), obtained by digestion with Acromobacter protease 1, formed amyloid-like fibrils in 50% (v/v) 2,2,2-trifluoroethanol and 10 mM HCl at 25 degreesC, as confirmed by thioflavin T fluorescence, circular dichroism spectra, and atomic force microscopy images. A synthetic K3 peptide composed of D-amino acids (D-K3 peptide) formed similar fibrils but with opposite chirality as indicated by circular dichroism spectra. A mixture of L-K3 and D-K3 peptides also formed fibrils, although the L- and D-amino acid composition of each fibril is unknown. To examine the possible cross-reactivity between L- and D-enantiomers, we carried out seeding experiments in which preformed seeds were extended by monomers. The results revealed that only the homologous extensions proceed smoothly, i.e., the growth of L-seeds by L-monomers or D-Seeds by D-monomers. The results suggest that, while the fibrils derived from L- and D-peptides form in a similar manner but with opposite stereochemistry, a cross-reaction between them is prevented because the geometry of the mixed sheet cannot satisfy dominant factors for beta-sheet stabilization.