Staggered side-chain conformers of aspartyl residues prerequisite to transformation from L-α- to D-β-aspartate 58 in human-lens αA-crystallin fragment.

D-β-aspartyl (Asp) residues are found in aged human-lens αA-crystallin. To explore why the uncommon D-β-Asp is accumulated, the stability of L-α-, D-α-, and D-β-Asp residues is compared in view of the staggered side-chain conformers. By using αA-crystallin fragment, T(55)VLD(58)SGISEVR(65), composed of Asp58 isomers, the vicinal spin-spin coupling constants of Asp58 Hα-Hβ1 and Hα-Hβ2 are quantified by high-resolution solution NMR.