Enantioselective Transesterification Catalysis by Nanosized Serine Protease Subtilisin Carlsberg Particles in Tetrahydrofuran

Enhanced Bioactivity of Enzyme/MOF Biocomposite via Host Framework Engineering

This study reports the successful development of a sustainable synthesis protocol for a phase-pure metal azolate framework (MAF-6) and its application in enzyme immobilization. An esterase@MAF-6 biocomposite was synthesized, and its catalytic performance was compared with that of esterase@ZIF-8 and esterase@ZIF-90 in transesterification reactions. Esterase@MAF-6, with its large pore aperture, showed superior enzymatic performance compared to esterase@ZIF-8 and esterase@ZIF-90 in catalyzing transesterification reactions using both n-propanol and benzyl alcohol as reactants. The hydrophobic nature of the MAF-6 platform was shown to activate the immobilized esterase into its open-lid conformation, which exhibited a 1.5- and 4-times enzymatic activity as compared to free esterase in catalyzing transesterification reaction using n-propanol and benzyl alcohol, respectively. The present work offers insights into the potential of MAF-6 as a promising matrix for enzyme immobilization and highlights the need to explore MOF matrices with expanded pore apertures to broaden their practical applications in biocatalysis.

Utilization of one novel deep-sea microbial protease sin3406-1 in the preparation of ethyl (S)-3-hydroxybutyrate through kinetic resolution

One novel protease sin3406-1 was identified from Streptomyces niveus SCSIO 3406, which was isolated from the deep sea of the South China Sea, and heterologously expressed in E. coli BL21(DE3). Protease sin3406-1 was further used as a green biocatalyst in the kinetic resolution of racemic ethyl-3-hydroxybutyrate. After careful process optimization, chiral product ethyl (S)-3-hydroxybutyrate was generated with an enantiomeric excess of over 99% and a conversion rate of up to 50% through direct hydrolysis of inexpensive racemic ethyl-3-hydroxybutyrate catalyzed by sin3406-1. Interestingly, protease sin3406-1 exhibited the same enantio-preference as that of esterase PHE21 during the asymmetric hydrolysis of the ester bonds of racemic ethyl-3-hydroxybutyrate. Through mutation studies and molecular docking, we also demonstrated that the four residues close to the catalytic center, S85, A86, Q87 and Y254, played key roles in both the hydrolytic activity and the enantioselectivity of protease sin3406-1, possibly through forming hydrogen bonds between the enzyme and the substrates. Deep-sea microbial proteases represented by sin3406-1 are new contributions to the biocatalyst library for the preparation of valuable chiral drug intermediates and chemicals through enzymatic kinetic resolution.

Improved Enantioselectivity of Subtilisin Carlsberg towards Secondary Alcohols by Protein Engineering

Generally, the catalytic activity of subtilisin Carlsberg (SC) for transacylation reactions with secondary alcohols in organic solvent is low. Enzyme immobilization and protein engineering was performed to improve the enantioselectivity of SC towards secondary alcohols. Possible amino-acid residues for mutagenesis were found by combining available literature data with molecular modeling. SC variants were created by site-directed mutagenesis and were evaluated for a model transacylation reaction containing 1-phenylethanol in THF. Variants showing high E values (>100) were found. However, the conversions were still low. A second mutation was made, and both the E values and conversions were increased. Relative to that shown by the wild type, the most successful variant, G165L/M221F, showed increased conversion (up to 36 %), enantioselectivity (E values up to 400), substrate scope, and stability in THF.