Identification and Characterization of a New 7-Aminocephalosporanic Acid Deacetylase from Thermophilic Bacterium Alicyclobacillus tengchongensis

Properties and biotechnological applications of microbial deacetylase

Deacetylases, a class of enzymes that can catalyze the hydrolysis of acetylated substrates to remove the acetyl group, used in producing various products with high qualities, are one of the most influential industrial enzymes. These enzymes are highly specific, non-toxic, sustainable, and eco-friendly biocatalysts. Deacetylases and deacetylated compounds have been widely applicated in pharmaceuticals, medicine, food, and the environment. This review synthetically summarizes deacetylases' sources, characterizations, classifications, and applications. Moreover, the typical structural characteristics of deacetylases from different microbial sources are summarized. We also reviewed the deacetylase-catalyzed reactions for producing various deacetylated compounds, such as chitosan-oligosaccharide (COS), mycothiol, 7-aminocephalosporanic acid (7-ACA), glucosamines, amino acids, and polyamines. It is aimed to expound on the advantages and challenges of deacetylases in industrial applications. Moreover, it also serves perspectives on obtaining promising and innovative biocatalysts for enzymatic deacetylation. KEYPOINTS: • The fundamental properties of microbial deacetylases of various microorganisms are presented. • The biochemical characterizations, structures, and catalyzation mechanisms of microbial deacetylases are summarized. • The applications of microbial deacetylases in food, pharmaceutical, medicine, and the environment were discussed.

Biochemical characterization of an acetylesterase from Bacillus subtilis and its application for 7-aminocephalosporanic acid deacetylation

Deacetyl-7-aminocephalosporanic acid (D-7-ACA), which could be converted from 7-aminocephalosporanic acid (7-ACA), is a crucial starting material that is used for synthesizing industrial semisynthetic β-lactam antibiotics. Enzymes involved in the conversion from 7-ACA to D-7-ACA present critical resources in the pharmaceutical industry. In the present study, a putative acetylesterase, EstSJ, identified from Bacillus subtilis KATMIRA1933, was first heterologously expressed in Escherichia coli BL21(DE3) cells and biochemically characterized. EstSJ belongs to carbohydrate esterase family 12 and is active on short-chain acyl esters from p-NPC₂ to p-NPC₆. Multiple sequence alignments showed that EstSJ was also an SGNH family esterase with a typical GDS(X) motif at its N-terminal end and a catalytic triad composed of Ser¹⁸⁶-Asp³⁵⁴-His³⁵⁷. The purified EstSJ displayed the highest specific activity of 1,783.52 U mg^-1 at 30°C and pH 8.0, and was stable within the pH range of 5.0-11.0. EstSJ can deacetylate the C3' acetyl group of 7-ACA to generate D-7-ACA, and the deacetylation activity was 4.50 U mg^-1. Based on the structural and molecular docking with 7-ACA, the catalytic active sites (Ser¹⁸⁶-Asp³⁵⁴-His³⁵⁷) together with four substrate-binding residues (Asn²⁵⁹, Arg²⁹⁵, Thr³⁵⁵, and Leu³⁵⁶) of EstSJ are revealed. This study provided a promising 7-ACA deacetylase candidate that could be applied to produce D-7-ACA from 7-ACA in the pharmaceutical industry.

Structural insights into the putative bacterial acetylcholinesterase ChoE and its substrate inhibition mechanism

Mammalian acetylcholinesterase (AChE) is well-studied, being important in both cholinergic brain synapses and the peripheral nervous systems and also a key drug target for many diseases. In contrast, little is known about the structures and molecular mechanism of prokaryotic acetylcholinesterases. We report here the structural and biochemical characterization of ChoE, a putative bacterial acetylcholinesterase from Pseudomonas aeruginosa Analysis of WT and mutant strains indicated that ChoE is indispensable for P. aeruginosa growth with acetylcholine as the sole carbon and nitrogen source. The crystal structure of ChoE at 1.35 Å resolution revealed that this enzyme adopts a typical fold of the SGNH hydrolase family. Although ChoE and eukaryotic AChEs catalyze the same reaction, their overall structures bear no similarities constituting an interesting example of convergent evolution. Among Ser-38, Asp-285, and His-288 of the catalytic triad residues, only Asp-285 was not essential for ChoE activity. Combined with kinetic analyses of WT and mutant proteins, multiple crystal structures of ChoE complexed with substrates, products, or reaction intermediate revealed the structural determinants for substrate recognition, snapshots of the various catalytic steps, and the molecular basis of substrate inhibition at high substrate concentrations. Our results indicate that substrate inhibition in ChoE is due to acetate release being blocked by the binding of a substrate molecule in a nonproductive mode. Because of the distinct overall folds and significant differences of the active site between ChoE and eukaryotic AChEs, these structures will serve as a prototype for other prokaryotic acetylcholinesterases.

Characterization and Immobilization of a Novel SGNH Family Esterase (LaSGNH1) from Lactobacillus acidophilus NCFM

The SGNH family esterases are highly effective biocatalysts due to their strong catalytic efficiencies, great stabilities, relatively small sizes, and ease of immobilization. Here, a novel SGNH family esterase (LaSGNH1) from Lactobacillus acidophilus NCFM, which has homologues in many Lactobacillus species, was identified, characterized, and immobilized. LaSGNH1 is highly active towards acetate- or butyrate-containing compounds, such as p-nitrophenyl acetate or 1-naphthyl acetate. Enzymatic properties of LaSGNH1, including thermal stability, optimum pH, chemical stability, and urea stability, were investigated. Interestingly, LaSGNH1 displayed a wide range of substrate specificity that included glyceryl tributyrate, tert-butyl acetate, and glucose pentaacetate. Furthermore, immobilization of LaSGNH1 by crosslinked enzyme aggregates (CLEAs) showed enhanced thermal stability and efficient recycling property. In summary, this work paves the way for molecular understandings and industrial applications of a novel SGNH family esterase (LaSGNH1) from Lactobacillus acidophilus.

Identification and characterization of an acetyl esterase from Paenibacillus sp. XW-6-66 and its novel function in 7-aminocephalosporanic acid deacetylation

OBJECTIVES

To obtain a new acetyl esterase from Paenibacillus sp. XW-6-66 and apply the enzyme to 7-aminocephalosporanic acid (7-ACA) deacetylation.

RESULTS

The acetyl esterase AesZY was identified from Paenibacillus sp. XW-6-66, and its enzymatic properties were investigated. With the putative catalytic triad Ser114-Asp203-His235, AesZY belongs to the Acetyl esterase (Aes) family which is included in the α/β hydrolase superfamily and contains the consensus Gly-X-Ser-X-Gly motif. The maximum activity of AesZY was detected at pH 8.0 and 40 °C. AesZY was stable at different pH values ranging from 5.0 to 12.0, and was tolerant to several metal ions. Furthermore, the deacetylation activity of AesZY toward 7-ACA was approximately 7.5 U/mg, and the K_cat/K_m value was 2.04 s^-1 mM^-1.

CONCLUSIONS

Our results demonstrate the characterization of a new acetyl esterase belonging to the Aes family with potential biotechnological applications.

Understanding the structural and functional properties of carbohydrate esterases with a special focus on hemicellulose deacetylating acetyl xylan esterases

Acetyl and methyl esterifications are two major naturally found substitutions in the plant cell-wall polysaccharides. The non-cellulosic plant cell-wall polysaccharides such as pectin and hemicellulose are differentially esterified by the O-acetyl and methyl groups to cease the action of various hydrolytic enzymes secreted by different fungi and bacterial species. Thus, microorganisms have emerged with a special class of enzymes known as carbohydrate esterases (CE). The CE catalyse O-de, N-deacetylation of acetylated saccharide residues (esters or amides, where sugars play the role of alcohol/amine/acid). Carbohydrate active enzyme (CAZy) database has classified CE into 16 classes, of which hemicellulose deacetylating CE were grouped into eight classes (CE-1 to CE-7 and CE-16). Various plant biomass degrading fungi and bacteria secretes acetyl xylan esterases (AcXE); however, these enzymes exhibit varied substrate specificities. AcXE and xylanases-coupled pretreatment methods exhibit significant applications, such as enhancing animal feedstock, baking industry, production of food additives, paper and pulp, xylitol production and biorefinery-based industries, respectively. Thus, understanding the structural and functional properties of acetyl xylan esterase will significantly aid in developing the efficient AcXE with wide range of industrial applications.

Identification, characterization, immobilization, and mutational analysis of a novel acetylesterase with industrial potential (LaAcE) from Lactobacillus acidophilus

Lactic acid bacteria, which are involved in the fermentation of vegetables, meats, and dairy products, are widely used for the productions of small organic molecules and bioactive peptides. Here, a novel acetylesterase (LaAcE) from Lactobacillus acidophilus NCFM was identified, functionally characterized, immobilized, and subjected to site-directed mutagenesis for biotechnological applications. The enzymatic properties of LaAcE were investigated using biochemical and biophysical methods including native polyacrylamide gel electrophoresis, acetic acid release, biochemical assays, enzyme kinetics, and spectroscopic methods. Interestingly, LaAcE exhibited the ability to act on a broad range of substrates including glucose pentaacetate, glyceryl tributyrate, fish oil, and fermentation-related compounds. Furthermore, immobilization of LaAcE showed good recycling ability and high thermal stability compared with free LaAcE. A structural model of LaAcE was used to guide mutational analysis of hydrophobic substrate-binding region, which was composed of Leu¹⁵⁶, Phe¹⁶⁴, and Val²⁰⁴. Five mutants (L156A, F164A, V204A, L156A/F164A, and L156A/V204A) were generated and investigated to elucidate the roles of these hydrophobic residues in substrate specificity. This work provided valuable insights into the properties of LaAcE, and demonstrated that LaAcE could be used as a model enzyme of acetylesterase in lactic acid bacteria, making LaAcE a great candidate for industrial applications.

A key esterase required for the mineralization of quizalofop-p-ethyl by a natural consortium of Rhodococcus sp. JT-3 and Brevundimonas sp. JT-9

A natural consortium, named L1, of Rhodococcus sp. JT-3 and Brevundimonas sp. JT-9 was obtained from quizalofop-p-ethyl (QE) polluted soil. The consortium was able to use QE as a sole carbon source for growth and degraded 100mgL^-1 of QE in 60h. Strain JT-3 initiated the catabolism of QE to quizalofop acid (QA), which was used by strain JT-9 as carbon source for growth and to simultaneously feed strain JT-3. A novel esterase EstS-JT, which was responsible for the transformation of QE to QA and essential for the mineralization of QE by the consortium, was cloned from strain JT-3. EstS-JT showed low amino acid identity to other reported esterases from esterase family VIII and represents a new member of this family. The deduced amino acid sequence contained the esterase family VIII conserved motifs S-X-X-K, YSV and WAG. The purified recombinant EstS-JT displayed maximal esterase activity at 35°C and pH 7.5. An inhibitor assay, site-directed mutagenesis and 3D modeling analysis revealed that S₆₄, K₆₇ and Y₁₇₅ were essential for catalysis and probably comprised the catalytic center of EstS-JT. Additionally, EstS-JT had broad substrate specificity and was capable of hydrolyzing p-nitrophenyl esters (C₂-C₈) and various AOPP herbicides.

Characterization of a novel SGNH-type esterase from Lactobacillus plantarum

Lactic acid bacteria (LAB) are sources of a large variety of microbial ester hydrolases because they can produce a wide range of short-chain esters, phenolic alcohols, and fatty acids. Here, a novel SGNH-type esterase (LpSGNH1) from Lactobacillus plantarum WCFS1 was identified, functionally characterized, and immobilized for biotechnological applications. Homologs of LpSGNH1 are also found in many lactic acid bacteria (LAB) species. Biochemical features of LpSGNH1 were investigated using mass spectrometry, gel filtration chromatography, enzyme kinetics, fluorescence, and circular dichroism (CD) spectroscopy. LpSGNH1 were retained its activity under conditions that would be encountered during fermentations. Interestingly, LpSGNH1 exhibited the ability to act on a broad range of substrates including ketoprofen acetate, cefotaxime (CTX), and 7-aminocephalosporanic acid (7-ACA) as well as glucose pentaacetate, acetylxylan, and acetylalginate, which make LpSGNH1 a great candidate for extensive industrial applications. Furthermore, cross-linked enzyme aggregates of LpSGNH1 (CLEA-LpSGNH1) displayed recycling ability and thermal stability compared to free LpSGNH1, which could be useful for industrial applications. This work highlights the importance of LpSGNH1 in the preparation of commercial compounds, and LpSGNH1 can be used as a model system of SGNH esterases in lactic acid bacteria.