The crosslinking sites and molecular conformation of gelatin hydrogel modified by transglutaminase

This work aimed to investigate the covalent crosslinking sites induced by transglutaminase (TGase, EC 2.3.2.13) in gelatin hydrogel and their impact on the gelatin molecular conformation. LC-MS/MS results demonstrated that Lys644 and Gln648 of α1 chain and Gln19 of α2 chain were the main sites. The results of molecular dynamic (MD) simulation indicated that at the moderate degree of covalent crosslinking (13.55%), Radius of gyration (Rg) values decreased from 11.5 to 10.0 nm at 4°C and led to a more compact structure, therefore enhancing structural tightness and gel strength. As the degree of crosslinking rose, the number of crosslinking sites gradually increased, with a predominant distribution in the C-terminal pro-peptide of gelatin chain. At the high crosslinking degree (37.48%), Rg value decreased at 100°C and gelatin chains were connected through a “head to tail” linkage configuration, resulting in a significant reduction in the triple helix-like structure. The structure maintained the gel-forming ability at high temperature while lowering the aggregation energy of water molecules from -2.359 × 105 to -2.455 ×105 kJ/mol, leading to thermal irreversibility of gelatin hydrogel.