Metal ion of metal-organic frameworks facilitating immobilized chitinase performance

Metal-organic framework (MOF) structures containing different metal ions and 1,3,5-trimesic acid (BTC) were fabricated, as the carriers to immobilize chitinase (Chi) for improving the performance of Chi, for the first time. It was found that the immobilization of Chi on Ca-BTC, Ba-BTC, and Ni-BTC increased its activity. Notably, the specific activity of Chi@Ca-BTC was enhanced by 2.1 times that of free Chi, reaching 16.27 U/mg. The catalytic efficiency and substrate affinity of Chi@Ca-BTC were also remarkably improved, confirmed by the kcat/Km enhancement (4.2 times) and Km value reduction (40 %). Moreover, the half-life of Chi@Ca-BTC at the optimum pH 6.0 and 55 degrees C was prolonged from 1.8 h to 6.8 h. More than 80 % of enzyme activity was retained after 22 cycles of usage, showing superior reusability. It was proved that Ca2+ on MOF surface enhanced the formation of hydrogen bonds between the catalytic key amino acid Glu-405 and substrate, accelerating the enzymatic catalysis. Then, Chi@Ca-BTC was employed as an outstanding biocatalytic platform for the degradation of chitin, with 8.1 times increase in conversion efficiency. Such a MOF-based immobilization strategy for improving enzymatic performance is of considerable reference value in designing advanced immobilized enzyme for various polysaccharide biocatalytic reaction.