Gigantol disrupts AR and iNOS conformation and promotes aggregation through direct molecular interaction to suppress diabetic cataract.

Diabetic cataract (DC) is a major cause of vision impairment, partly driven by the pathological roles of aldose reductase (AR) and inducible nitric oxide synthase (iNOS). Gigantol, a bibenzyl compound derived from Dendrobium, has shown potential in preventing DC, yet its molecular mechanism remains incompletely understood. In this study, we investigated the modulation of conformational integrity and aggregation propensity of AR/iNOS by gigantol using fluorescent labeling, fluorescence resonance energy transfer (FRET), single-molecule imaging in living cells, fluorescence spectroscopy, confocal Raman spectroscopy, and atomic force microscopy (AFM). FRET analysis revealed interaction distances of 3.02 ± 0.22 nm for gigantol-AR and 5.07 ± 0.23 nm for gigantol-iNOS, with energy transfer efficiencies of 38.37 ± 4.76 % and 28.15 ± 3.52 %, respectively. Gigantol spontaneously bound to AR and iNOS via hydrogen bonds and van der Waals forces, inducing conformational changes in tyrosine and tryptophan microenvironments. Raman spectroscopy indicated significant alterations in α-helix and β-sheet structures, and AFM directly visualized protein aggregation upon gigantol treatment. These findings demonstrate that gigantol disrupts the conformational integrity of AR and iNOS and promotes their aggregation, thereby inhibiting their activity and providing a molecular basis for its anti-DC potential.