Selectively 2H-labeled Glu/Asp: application to pKa measurements in Abeta amyloid peptides.

Human Abeta peptides have been linked to Alzheimer's disease, and it is hypothesized that formation of amyloid as well as neurotoxicity are important events in the etiology of the disease. Previous studies have shown that the soluble precursor to Alzheimer's amyloid undergoes a pH-dependent folding transition as the self-assembly activity appears, and based upon inter-residue proximities, it was suspected that stabilization of the soluble form might rely upon formation of an intramolecular salt-bridge. However, pKa studies on a model 17-residue Abeta fragment supported an electrostatic model where a solvation imperative for charged side-chain atoms drives the folding process. To explore this model in an active 26-residue fragment as well as the full-length 40-residue Abeta peptide, pKa measurements were performed via 1H and 2H NMR. To overcome issues related to sensitivity and spin system degeneracy, specifically deuterated allyl protected-Fmoc amino acids were synthesized for incorporation into a series of peptides, and a high sensitivity 2H observe NMR probe was constructed.