Glycation induced active site disruption of Biliverdin IXβ reductase: A molecular dynamics approach.

Flavin reductase (FR), also known as Biliverdin IXβ Reductase (BLVRB), is a monomeric enzyme belonging to the short-chain dehydrogenase/reductase (SDR) protein family, characterized by its NADPH-dependent catalytic conversion of biliverdin to bilirubin, a key antioxidant in fetal heme catabolism and cellular defense. Structurally, BLVRB features a Rossmann-fold domain with dynamic loop regions (Loop80 and Loop120) and coenzyme clamps (Arg14, Arg78) critical for substrate and cofactor binding. Under hyperglycemic conditions, BLVRB undergoes glycation by methylglyoxal (MG), further enhancing the diabetic complications due to advanced glycation end-products (AGEs) production. Here, molecular dynamics simulations were employed to examine glycation-induced structural changes. Results reveal a transition from open to closed loop conformations, tighter Thr12-Arg78 clamp association, narrowed NADPH binding pocket, reduced solvent accessibility, and altered interhelical orientations. Principal Component Analysis (PCA) and Free Energy Landscape (FEL) analyses confirmed significant shifts in conformational space and stability. These findings suggest glycation disrupts BLVRB dynamics, potentially impairing activity and its antioxidant function.