Investigation of a Peptide Responsible for Amyloid Fibril Formation of β2-Microglobulin byAchromobacter Protease I

Abstract To obtain insight into the mechanism of amyloid fibril formation from β2-microglobulin (β2-m), we prepared a series of peptide fragments using a lysine-specific protease from Achromobacter lyticus and examined their ability to form amyloid fibrils at pH 2.5. Among the nine peptides prepared by the digestion, the peptide Ser20–Lys41 (K3) spontaneously formed amyloid fibrils, confirmed by thioflavin T binding and electron microscopy. The fibrils composed of K3 peptide induced fibril formation of intact β2-m with a lag phase, distinct from the extension reaction without a lag phase observed for intact β2-m seeds. Fibril formation of K3 peptide with intact β2-m seeds also exhibited a lag phase. On the other hand, the extension reaction of K3 peptide with the K3 seeds occurred without a lag phase. At neutral pH, the fibrils composed of either intact β2-m or K3 peptide spontaneously depolymerized. Intriguingly, the depolymerization of K3 fibrils was faster than that of intact β2-m fibrils. These results indicated that, although K3 peptide can form fibrils by itself more readily than intact β2-m, the K3 fibrils are less stable than the intact β2-m fibrils, suggesting a close relation between the free energy barrier of amyloid fibril formation and its stability.