Application-Oriented Marine Isomerases in Biocatalysis

The class EC 5.xx, a group of enzymes that interconvert optical, geometric, or positional isomers are interesting biocatalysts for the synthesis of pharmaceuticals and pharmaceutical intermediates. This class, named “isomerases,” can transform cheap biomolecules into expensive isomers with suitable stereochemistry useful in synthetic medicinal chemistry, and interesting cases of production of l-ribose, d-psicose, lactulose, and d-phenylalanine are known. However, in two published reports about potential biocatalysts of marine origin, isomerases are hardly mentioned. Therefore, it is of interest to deepen the knowledge of these biocatalysts from the marine environment with this specialized in-depth analysis conducted using a literature search without time limit constraints. In this review, the focus is dedicated mainly to example applications in biocatalysis that are not numerous confirming the general view previously reported. However, from this overall literature analysis, curiosity-driven scientific interest for marine isomerases seems to have been long-standing. However, the major fields in which application examples are framed are placed at the cutting edge of current biotechnological development. Since these enzymes can offer properties of industrial interest, this will act as a promoter for future studies of marine-originating isomerases in applied biocatalysis.

Improved substrate specificity for D-galactose of L-arabinose isomerase for industrial application

L-Arabinose isomerase isolated from Geobacillus stearothermophilus (GSAI) was modified to improve its substrate specificity for D-galactose for the production of D-tagatose, a potential reduced-energy sweetener. Among the selected residues, mutation at residue 18 produced a mutant strain, H18T, which exhibited increased activity for D-galactose compared with the wild-type (WT) enzyme. Analysis of the substrate specificity of H18T showed a 45.4% improvement for D-galactose. Replacing histidine with threonine at residue 18 resulted in approximately 2.7-fold and 1.8-fold higher substrate binding and catalytic efficiency, respectively, for D-galactose. Further enhancement of the specific activity and catalytic efficiency of H18T for D-galactose by up to 2.7-fold and 4.3-fold, respectively, was achieved by adding borate during L-arabinose isomerase catalysis. Moreover, H18T showed thermostability and no destabilization was detected, which is promising for the industrial production of D-tagatose.