Mg²⁺-induced stabilization of β-galactosidase from Bacillus megaterium and its application in the galactosylation of natural products

Objective: To improve the stability of β-galactosidase from Bacillus megaterium YZ08 (BMG) in aqueous hydrophilic solvents and promote its application in the galactosylation of natural products. Results: The addition of 5 mM Mg²⁺ significantly enhanced the stability of BMG in aqueous hydrophilic solvents, and the half-lives of BMG in these solutions reached 56 min to 208 h, while they were only 7 min to 5.9 h without addition of Mg²⁺. Studies on the kinetic parameters in buffer solution and 30% dimethyl sulfoxide (DMSO) indicated that the affinity of BMG to 2-nitrophenyl-β-d-galactopyranoside and its catalytic efficiency (κ_cat/K_m) increased with the addition of Mg²⁺. Furthermore, the addition of Mg²⁺ facilitated galactosylation reactions in 30% DMSO and increased product conversions by 24–41% due to the reversal of the thermodynamic equilibrium of hydrolysis. Conclusion: A convenient approach was established to improve the stability of BMG in aqueous hydrophilic solvents.