Characterization and Consensus-Based Thermostabilization of a Specific GH107 Fucoidanase for the Production of <i>Saccharina japonica</i> Fuco-Oligosaccharides

Saccharina japonica fucoidan’s complex, heterogeneously sulfated structure hinders the preparation of well-defined fuco-oligosaccharides (FOs). While enzymatic depolymerization offers a mild and selective route, efficient enzymes specifically tailored for S. japonica fucoidan remain scarce. Here, we identified and characterized OUC-MgFucD1, a novel GH107 family fucoidanase from Mariniflexile gromovii, exhibiting unprecedented substrate specificity. OUC-MgFucD1 exclusively cleaves α-(1→3)-linked regions of S. japonica fucoidan, producing sulfated mono-, di-, and tetrasaccharides. Its hydrolysis pattern is strictly modulated by local sulfation motifs. To enhance industrial applicability, a consensus-based rational design approach integrating three complementary platforms was employed to develop a stabilized variant, OUC-MgFucD1-H359D. This engineered enzyme exhibits exceptional thermal robustness, retaining over 60% activity after 12 h at 40 °C, whereas the wild-type enzyme undergoes complete inactivation. Our findings underscore the functional diversity of GH107 family, providing a robust molecular framework and an efficiency enzymatic tool for the precision-tailored valorization of S. japonica fucoidan into FOs.