Spectroscopic study on the effects of nonenzymatic glycation in human alpha-crystallin

Nonenzymatic glycated lens alpha-crystallin, isolated from human diabetic cataract lenses, does not differ in subunit size and secondary structure from nonglycated alpha-crystallin. The tertiary structure, however, has undergone a significant change as reflected in the changes of near-ultraviolet (UV) circular dichroism (CD) and fluorescence of intrinsic probes (tryptophan, nontryptophan) and extrinsic probes [(MIANS (6-(4'-maleimidylanilino)naphthalene-2-sulfonic acid) and TNS (6-(p-toluidinyl)naphthalene-2-sulfonate)]. A decrease in tryptophan fluorescence and an increase in nontryptophan fluorescence were observed for glycated alpha-crystallin. Decreased intensities of SH-specific fluorescent probes (MIANS) and hydrophobic probe (TNS) also were observed. The near UV CD and TNS polarization results suggest a more unfolded structure of the glycated crystallin. The significant decrease of sulfhydryl groups in glycated protein suggests that glycation facilitates a further secondary change.