Solvent accessibility to aspartyl and succinimidyl residues at positions 7and 23 in the amyloid beta 1-28 peptide

The water accessibilities to aspartyl residues at positions 7 and 23 in the amyloid beta 1-28 peptide associated with Alzheimer's Disease have been ca lculated using different techniques. These accessibilities of water were co mpared to those of the succinimidyl residues (SUC) replacing the aspartyl o nes (ASP). It has been possible to ascertain that these modifications (ASP --> SUC) lead to a significant increase in the water accessibility to the b ackbone and alpha-carbon atom of the SUC7 and SUC23 residues. It is suggest ed that the spontaneous transformation of ASP --> SUC might lead to an incr ease of the racemization rates due to the higher accessibility of water at these sites. It is also proposed that the behavior of the adjacent residues in the selectivity of the racemization is to control the water accessibili ty at the reactive residue.