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.