Preparation of Ficin Complexes with Carboxymethylchitosan and <i>N</i>-(2-Hydroxy)propyl-3-Trimethyl Ammonium Chitosan and the Study of Their Structural Features

Abstract

Chitosan derivatives – сarboxymethyl chitosan and N-(2-hydroxy)propyl-3-trimethyl ammonium chitosan with molecular weights of 200, 350, and 600 kDa have been synthesized. Complexes of ficin with chitosan and its named derivatives have been obtained. IR spectra of chitosan, carboxymethylchitosan, and N-(2-hydroxy)propyl-3-trimethyl ammonium chitosan and their complexes with ficin were recorded. The analysis of the spectra confirmed the formation of conjugates between the macromolecules of polysaccharides and ficin. The optimal ratio of protein content (0.7 mg/g of carrier) and specific activity (1590 units/mg of protein) was found during the complexation of ficin with the N-(2-hydroxy)propyl-3-trimethylammonium chitosan matrix with the molecular weight 350 kDa. The efficiency of ficin complexation (in terms of specific catalytic activity) with N-(2-hydroxy)propyl-3-trimethyl ammonium chitosan (350 kDa) exceeds that of chitosan (350 kDa) and carboxymethylchitosan (350 kDa) 2.4 and 9.8 times respectively. The types of interactions, first binding energies, amino acid composition of ficin surfaces, which interact with the carrier in the process of complexation, were studied by molecular docking. It has been established that bonds and interactions with chitosan and its derivatives are formed, among other things, with the participation of amino acid residues located near the ficin active site (Cys25 and His162), which explains the change in the proteolytic activity of the obtained complexes. Ficin complexes with N-(2-hydroxy)propyl-3-trimethyl ammonium chitosan are soluble in a wide pH range and, therefore, may be more promising than protease-chitosan complexes in the development of medical preparations and biocatalysts for the food, brewing, and leather industries.