A systematic screen of beta(2)-microglobulin and insulin for amyloid-like segments.

Identifying sequence determinants of fibril-forming proteins is crucial for understanding the processes causing >20 proteins to form pathological amyloid depositions. Our approach to identifying which sequences form amyloid-like fibrils is to screen the amyloid-forming proteins human insulin and beta(2)-microglobulin for segments that form fibrils. Our screen is of 60 sequentially overlapping peptides, 59 being six residues in length and 1 being five residues, covering every noncysteine-containing segment in these two proteins. Each peptide was characterized as amyloid-like or nonfibril-forming. Amyloid-like peptides formed fibrils visible in electron micrographs or needle-like microcrystals showing a cross-beta diffraction pattern. Eight of the 60 peptides (three from insulin and five from beta(2)-microglobulin) were identified as amyloid-like. The results of the screen were used to assess the computational method, and good agreement between prediction and experiments was found. This agreement suggests that the pair-of-sheets, zipper spine model on which the computational method is based is at least approximately correct for the structure of the fibrils and suggests the nature of the sequence signal for formation of amyloid-like fibrils.