Protein engineering study of β-mannosidase to set up a potential chemically efficient biocatalyst

This study is focused on the analysis and mutagenesis of β-mannosidase from Bacteroides thetaiotaomicron with the aim of broadening its substrate specificity to 2-acetamido-2-deoxy-β-D-mannopyranosyl (β-ManNAc) derivatives. Various conformations (⁴C₁, ⁴H₅ and ¹S₅) of native and modified ligands were docked to the binding site of the protein to determine the most suitable conformation of sugars for further hydrolysis. Key amino acid residues were mutated in silico focusing on stabilizing the acetamido group of β-ManNAc as well as forming the oxazoline intermediate needed for hydrolysis. The results of large set of 5 ns molecular dynamic simulations showed that the majority of the active site residues are involved in substrate interaction and do not exhibit a higher flexibility except for Asn178. Mutations of Asn178 to alanine and Asp199 to serine could lead to a stabilization of the acetamido group in the binding site. So far, in vitro mutagenesis and the screen of a large variety of biological sources were unable to extend β-mannosidase's activity to include β-ManNAc derivatives.