Functional Characterization of a Robust Marine Microbial Esterase and Its Utilization in the Stereo-Selective Preparation of Ethyl (S)-3-Hydroxybutyrate

Unraveling the substrate-binding pocket: Endowing carbonyl reductase BaSDRX with intriguing inconsistent stereoselectivity towards similar structured β-Ketoesters

Tailoring of carbonyl reductase with desired stereoselectivity for the asymmetric reduction of given β-ketoesters continues to pose a significant challenge. The reconstruction of substrate-binding pocket endowed carbonyl reductase BaSDRX with inconsistent stereoselectivity towards similar structured β-ketoesters. The variant F86C/E142A showed reversed stereoselectivity towards β-ketoesters with a larger substituent on the carbonyl side, giving antiPrelog alcohols with ee values varied from 52.8 % to 95.8 %. However, it displayed only a decreased stereoselectivity for β-ketoesters that contain a smaller methyl group at the same position. Analysis of enzyme-substrate complexes showed that a newly formed groove provided more spaces and chances for β-ketoester with a larger substituent on the carbonyl side to approach the catalytic triad of F86C/E142A in antiPrelog-preferred binding modes. For the β-ketoesters with a smaller methyl group on the carbonyl side, the introduction of mutations exerted less effect on the proximity of the substrate with antiPrelog-preferred binding modes to the catalytic residues. Meanwhile, both β-ketoesters with smaller group and larger group on carbonyl side underwent minor alterations in Prelog-preferred conformation. All of these made the variant F86C/E142A exhibited inconsistent stereoselectivity towards β-ketoesters possessing analogous structure. These results offered detailed mechanisms that govern the stereoselectivity in the enzyme-mediated asymmetric reduction of β-ketoesters.

Marine Pseudomonas: diving into the waves of blue biotechnology

From marine to terrestrial environments, Pseudomonas spp. exhibit a remarkable ability not only to adapt but also thrive even amidst adverse conditions. This fact turns Pseudomonas spp. into one of the most prominent candidates for novel biotechnological solutions. Even though terrestrial isolates have been extensively studied, there is still an almost untapped source to be explored in marine Pseudomonas. Harnessing such strains offers an opportunity to discover novel bioactive compounds that could address current global challenges in healthcare and sustainable development. Therefore, this minireview aimed to provide an overview of the main recent discoveries regarding antimicrobials, antifouling, enzymes, pigments, and bioremediation strategies derived from marine isolates of Pseudomonas spp. Future research perspectives will also be discussed to foster forthcoming endeavors to explore the marine counterparts of such a prolific bacterial genus.

Characterization of the role of esterases in the biodegradation of organophosphate, carbamate, and pyrethroid pesticides

Ester-containing organophosphate, carbamate, and pyrethroid (OCP) pesticides are used worldwide to minimize the impact of pests and increase agricultural production. The toxicity of these chemicals to humans and other organisms has been widely reported. Chemically, these pesticides share an ester bond in their parent structures. A particular group of hydrolases, known as esterases, can catalyze the first step in ester-bond hydrolysis, and this initial regulatory metabolic reaction accelerates the degradation of OCP pesticides. Esterases can be naturally found in plants, animals, and microorganisms. Previous research on the esterase enzyme mechanisms revealed that the active sites of esterases contain serine residues that catalyze reactions via a nucleophilic attack on the substrates. In this review, we have compiled the previous research on esterases from different sources to determine and summarize the current knowledge of their properties, classifications, structures, mechanisms, and their applications in the removal of pesticides from the environment. This review will enhance the understanding of the scientific community when studying esterases and their applications for the degradation of broad-spectrum ester-containing pesticides.

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.

Utilization of deep-sea microbial esterase PHE21 to generate chiral sec-butyl acetate through kinetic resolutions

We previously identified and characterized 1 novel deep-sea microbial esterase PHE21 and used PHE21 as a green biocatalyst to generate chiral ethyl (S)-3-hydroxybutyrate, 1 key chiral chemical, with high enantiomeric excess and yield through kinetic resolution. Herein, we further explored the potential of esterase PHE21 in the enantioselective preparation of secondary butanol, which was hard to be resolved by lipases/esterases. Despite the fact that chiral secondary butanols and their ester derivatives were hard to prepare, esterase PHE21 was used as a green biocatalyst in the generation of (S)-sec-butyl acetate through hydrolytic reactions and the enantiomeric excess, and the conversion of (S)-sec-butyl acetate reached 98% and 52%, respectively, after process optimization. Esterase PHE21 was also used to generate (R)-sec-butyl acetate through asymmetric transesterification reactions, and the enantiomeric excess and conversion of (R)-sec-butyl acetate reached 64% and 43%, respectively, after process optimization. Deep-sea microbial esterase PHE21 was characterized to be a useful biocatalyst in the kinetic resolution of secondary butanol and other valuable chiral secondary alcohols.

Functional characterization of salt-tolerant microbial esterase WDEst17 and its use in the generation of optically pure ethyl (R)-3-hydroxybutyrate

The two enantiomers of ethyl 3-hydroxybutyrate are important intermediates for the synthesis of a great variety of valuable chiral drugs. The preparation of chiral drug intermediates through kinetic resolution reactions catalyzed by esterases/lipases has been demonstrated to be an efficient and environmentally friendly method. We previously functionally characterized microbial esterase PHE21 and used PHE21 as a biocatalyst to generate optically pure ethyl (S)-3-hydroxybutyrate. Herein, we also functionally characterized one novel salt-tolerant microbial esterase WDEst17 from the genome of Dactylosporangium aurantiacum subsp. Hamdenensis NRRL 18085. Esterase WDEst17 was further developed as an efficient biocatalyst to generate (R)-3-hydroxybutyrate, an important chiral drug intermediate, with the enantiomeric excess being 99% and the conversion rate being 65.05%, respectively, after process optimization. Notably, the enantio-selectivity of esterase WDEst17 was opposite than that of esterase PHE21. The identification of esterases WDEst17 and PHE21 through genome mining of microorganisms provides useful biocatalysts for the preparation of valuable chiral drug intermediates.