Conformational studies on amyloidb peptide (Ab) in aqueous solution are complicated by its tendency to aggregate. In this study, we determined the atomic-level structure of Ab28)42 in an aqueous environment. We fused fragments of Ab, residues 10–24 (Ab10)24) or 28–42 (Ab28)42), to three positions in the C-terminal region of ribonuclease HII from a hyper-thermophile, Thermococcus kodakaraensis(Tk-RNase HII).