Abstract
A novel esterase, EstCS1, was isolated from a compost metagenomics library. The EstCS1 protein, which consists of 309 amino acid residues with an anticipated molecular mass of 34 kDa, showed high amino acid sequence identities to predicted esterases and alpha/beta hydrolases (59%) from some cultured bacteria and to predicted lipases/esterases from uncultured bacteria. The phylogenetic analysis suggested that the EstCS1 belongs to the hormone-sensitive lipase family of lipolytic enzyme classification and contains a catalytic triad including Ser155–Asp255–His285. The Ser155 residue of the catalytic triad in the EstCS1 was located in the consensus active-site motif, GXSXG. Besides, a conserved HGGG motif placed in an oxyanion hole of the hormone-sensitive lipase family was discovered, too. The EstCS1 demonstrated the highest activity toward p-nitrophenyl propionate (C3) and caproate (C6) and was normally stable up to 60°C with optimal activity at 50°C. In addition, an optimal activity was observed at pH 8, and the EstCS1 possessed its stability within the pH range between 5 and 10. Interestingly, EstCS1 had an outstanding stability in up to 30% (v/v) organic solvents and activity over 50% in the presence of 50% (v/v) acetone, ethanol, dimethyl sulfoxide (DMSO), and N,N-dimethylformamide. The EstCS1 hydrolyzed sterically hindered tertiary alcohol esters of t-butyl acetate and linalyl acetate. Considering the properties, such as the moderate thermostability, stability against organic solvents, and activity toward esters of tertiary alcohols, the EstCS1 will be worthwhile to be used for organic synthesis and related industrial applications.
Highlights
Lipases (EC 3.1.1.3) and esterases (EC 3.1.1.1) are α/β hydrolases that are produced by a lot of microorganisms and eukaryotic organisms (Bornscheuer, 2002)
A BLAST search for sequence comparison among related proteins conducted at the National Center for Biotechnology Information (NCBI) obviously revealed that the amino acid sequence of EstCS1 had the high identities to lipolytic enzymes from various cultured and uncultured bacteria, including esterase and alpha/beta hydrolases from five cultured bacteria
The catalytic nucleophile serine is at position 155 in the consensus GXSXG pentapeptide and the HGGG motif in the oxyanion hole upstream of the pentapeptide motif; these are characteristics of family IV (HSL family) lipolytic enzymes (Figure 1A; Arpigny and Jaeger, 1999; Kim et al, 2015; Huo et al, 2018; Jayanath et al, 2018; Noby et al, 2018)
Summary
Lipases (EC 3.1.1.3) and esterases (EC 3.1.1.1) are α/β hydrolases that are produced by a lot of microorganisms and eukaryotic organisms (Bornscheuer, 2002). Lipolytic enzymes have drawn significant attention on account of useful and unique catalytic properties such as broad substrate specificity, organic solvent stability, position selectivity, and stereoselectivity, which is worthy of being used in agriculture, pharmaceutical, food, and fine chemical industries (Bornscheuer, 2002; Panda and Gowrishankar, 2005; Tutino et al, 2009). Bacterial and metagenomic lipolytic enzymes have been classified into 17 families (families I–XVII) according to their biological attributes and amino acid sequence (Arpigny and Jaeger, 1999; Castilla et al, 2017). Among the 17 families showing bacterial lipolytic enzymes, family IV showed noticeable sequence similarity to mammalian hormone-sensitive lipases (HSLs), which play a momentous role in regulation of lipid metabolism (Yeaman et al, 1994; Arpigny and Jaeger, 1999; Kim, 2017). A number of lipases and esterases belonging to family IV have been recently isolated from various environmental sources since the development of metagenomic analyses (Oh et al, 2012; Choi et al, 2013; Privé et al, 2015; Kim, 2017; Huo et al, 2018; Jayanath et al, 2018; Noby et al, 2018)
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