Preparation of a whole cell catalyst overexpressing acetohydroxyacid synthase of Thermotoga maritima and its application in the syntheses of α-hydroxyketones

Catalytic insights of acetolactate synthases from different bacteria

Acetolactate synthase (ALS) is an essential enzyme involved in the biosynthesis of platform chemicals acetoin and 2,3-butanediol in several microorganisms. In this study, we investigated the catalytic differences among three bacterial ALSs involved in the ligation of two molecules of pyruvate or 2-ketobutyrate. Based on the findings, we predicted three amino acid residues in each enzyme that caused a discrepancy in accordance with the multi-sequence alignment and molecular docking experiments: I398, A402, and T480 in Bacillus subtilis ALS; V400, Y404, and S482 in Listeria seleigeri serovar 1/2b ALS; and M394, H398, and G476 in Klebsiella pneumoniae ALS. Subsequently, we mutually mutated the residues in the three ALSs. The data obtained confirmed our inference that these three residues in each enzyme are truly correlated with substrate recognition, particularly in recognizing compounds that are larger than pyruvate, such as 2-ketobutyrate, benzaldehyde, and nitrosobenzene. This study further clarifies the biochemical traits of ALSs derived from various bacteria and expands the scope of ALS research.

Carboligation towards production of hydroxypentanones

2-Hydroxy-3-pentanone and 3-hydroxy-2-pentanone are flavor molecules present in various foods, such as cheese, wine, durian, and honey, where they impart buttery, hay-like, and caramel-sweet aromas. However, their utilization as flavoring agents is constrained by a lack of developed synthesis methods. In this study, we present their synthesis from simple starting compounds available in natural quality, catalyzed by previously characterized ThDP-dependent carboligases. Additionally, we demonstrate that newly discovered homologues of pyruvate dehydrogenase from E. coli (EcPDH E1), namely LaPDH from Leclercia adecarboxylata, CnPDH from Cupriavidus necator, and TcPDH from Tanacetum cinerariifolium, exhibit promising potential for α-hydroxy pentanone synthesis in form of whole-cell biocatalysts. Enzyme stability at varying pH levels, kinetic parameters, and reaction intensification were investigated. CnPDH, for example, exhibits superior stability across different pH levels compared to EcPDH E1. Both α-hydroxy pentanones can be produced with CnPDH in satisfactory yields (74% and 59%, respectively).

Overall analyses of the reactions catalyzed by acetohydroxyacid synthase/acetolactate synthase using a precolumn derivatization-HPLC method

A precolumn derivatization-HPLC method using 2,4-dinitrophenylhydrazine and 4-nitro-o-phenylenediamine as respective labeling reagents for comprehensive analyses of the reactions catalyzed by acetohydroxyacid synthase (AHAS)/acetolactate synthase (ALS) is developed and evaluated in this research. Comparison with the classic Bauerle' UV assay which can analyze the enzymes only through measurement of acetoin production, the HPLC method shows advantages because it can analyze the enzymes not only via determination of consumption of the substrate pyruvate, but also via measurement of formation of the products including acetoin, 2,3-butanedione, and acetaldehyde in the enzymatic reactions. Thus the results deduced from the HPLC method can reflect the trait of each enzyme in a more precise manner. As far as we know, this is the first time that the reactions mediated by AHAS/ALS using pyruvate as a single substrate are globally analyzed and the features of the enzymes are properly discussed.

The chemical mechanisms of the enzymes in the branched-chain amino acids biosynthetic pathway and their applications

l-Valine, l-isoleucine, and l-leucine are three key proteinogenic amino acids, and they are also the essential amino acids required for mammalian growth, possessing important and to some extent, special physiological and biological functions. Because of the branched structures in their carbon chains, they are also named as branched-chain amino acids (BCAAs). This review will highlight the advance in studies of the enzymes involved in the biosynthetic pathway of BCAAs, concentrating on their chemical mechanisms and applications in screening herbicides and antibacterial agents. The uses of some of these enzymes in lab scale organic synthesis are also discussed.