Fucooligosaccharides are the main group into the human milk oligosaccharides. Due to their beneficial properties, a series of synthetic methods have been proposed to obtain them. In this way, the α-L-fucosidase from Thermotoga maritima has emerged as a powerful catalyst for fucooligosaccharides production. Nonetheless, the limited options in substrates for transfucosylation reactions have delayed its wider application. Thus, the present work aimed to compare the reactivity of fucose, pNP-fucose, and ethyl-fucose, as well as the molecular interactions among these fucosyl-donors and the enzyme through a DFT study and docking analysis. DFT analysis was carried out through B3LYP/6-311++G(2d,2p) level of theory, while docking analysis was made for hydrolysis and transfucosylation procedures by Autodock VINA. Both anomers of lactose and fucosyl-donors were full geometry optimized in aqueous phase, and HOMO-LUMO descriptors were calculated. Therefore, band gaps from -7.14571 to -4.24429 eV were found, where α/β-pNP-fucose and α-fucose were the three more reactive compounds. Concerning docking study, coupling energies between -6.4 to -5.5 kcal·mol-1 were shown, being the α-pNP-fucose and α/β-ethyl-fucose the substrates with the lower enzyme affinity. In the case of lactose affinity to the complex β-fucose/enzyme, the disaccharide showed binding affinity energy of -5.7 and -5.8 kcal·mol-1 for the α- and β-anomer, respectively. As a consequence, results suggest that the best fucosyl-donors for hydrolysis are those who maintain lower affinity with the enzyme active site, while there is not a significant difference among lactose anomers for their bonding to the enzyme-substrate complex.
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