Amyloid beta peptide (A beta) adopts a helix-turn-helix conformation in membrane-mimicking solvents, organic solvents and detergents. However, A beta fragment, 28-42, adopts a beta-conformation in aqueous solution without organic solvents and detergents. We tried to determine the crystal structure of A beta fragment, 10-24, using fusion protein with ribonuclease HII from a hyperthermophile. Crystal structure analysis revealed that A beta(10-24) has disordered conformations. These results suggest that beta-structure formation of A beta(28-42) within full-length A in aqueous solution would nucleate and induce overall a-sheet fibrils. We propose a process for the conformational transition from a soluble form to the beta-structure of A beta in an aqueous environment.
