Characterization of new d-β-aspartate-containing proteins in a lens-derived cell line

Although proteins are generally composed of l-α-amino acids, biologically uncommon d-β-aspartic acid (Asp)-containing proteins have been reported in various tissues from elderly individuals. Our previous study indicated that the N/N1003A cell line, derived from rabbit lens, includes d-β-Asp-containing proteins of ∼50 kDa by Western blot analysis of a 2D-gel using a polyclonal antibody that is highly specific for d-β-Asp-containing proteins. In this study, we identified the d-β-Asp-containing proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and the Mascot online database searching algorithm. The results indicate that one of these 50 kDa proteins is an enolase showing homology with τ-crystallin. Other d-β-Asp-containing proteins, which we have recently discovered include lamin A/C, cytoplasmic NADP+-dependent isocitrate dehydrogenase, fructose-bisphosphate aldolase A, aldose reductase, l-lactate dehydrogenase A or calponin H2, phosphoglycerate mutase 1, phosphatidylethanolamine-binding protein, α-B-crystallin, and peptidyl-prolyl cis-trans isomerase A (PPlase).