Insights into the mechanism on the high-temperature activity of transglutaminase from Bacillus clausii and its crosslinked mode at protein level

Finding new crosslinking enzymes and elucidating internal cross-linking mode are beneficial to meeting the requirement of various protein substrates and processing conditions in food industry. Transglutaminase (TG) can lead to the covalent crosslink of ε-(γ-glutamine)-lysine isopeptidic bonds in proteins through acyl-transfer reaction. This work reported the characterization of transglutaminases (TGs) from four Bacillus strains with obvious differences in amino acid sequences and enzymatic properties. Among them, TG from B. clausii (BCLTG) displayed the highest optimal temperature (70 °C) and specific activity (282 U/mg). The molecular dynamics simulation indicated that enlargement of substrate accessible tunnel in BCLTG with the increased temperature might result in the easy approach of substrate molecule to the active center. Moreover, BCLTG could cause the crosslinking of bovine serum albumin and almost all protein constituents in whey protein and soy protein isolate, and the crosslinking path of BCLTG towards three proteins was revealed. This study provides an ideal candidate for proteins crosslinking and theoretical foundation and preliminary information for applying TG in food processing.