Characterization and immobilization of a novel SGNH hydrolase (Est24) from Sinorhizobium meliloti

Expression, characterization, and immobilization of a novel SGNH esterase Est882 and its potential for pyrethroid degradation

The widely-used pyrethroid pesticides have attracted public attention because of their potentials to cause environmental pollution and toxic effects on non-target organisms. Esterase is a kind of hydrolytic enzyme that can catalyze the cleavage or formation of ester bonds. it plays a pivotal role in the decomposition of pyrethroids and esters containing industrial pollutants through the hydrolysis of ester bonds. Here, a new esterase gene est882 was successfully screened, which encodes Est882, a SGNH family esterase composed of 294 amino acids. It was heterogeneously expressed, identified and immobilized. Multiple sequence alignment showed that Est882 had a typical GDS(X) conserved motif and a catalytic triad composed of Ser79, Asp269 and His275. Phylogenetic analysis showed that Est882 shall belong to a new esterase family. Biochemical characterization demonstrated that the optimum condition was 40°C and pH 9.0. Est882 immobilization was studied with mesoporous silica SBA-15 as the carrier and found to significantly improve the tolerance and stability of Est882. Its optimum pH increased to 10.0 and stabilized within pH 8.0-11.0. Free Est882 can effectively degrade various pyrethroids within 30 min, with a degradation rate above 80%. The immobilized Est882 yet degraded more than 70% of pyrethroids within 30 min. The present study indicated that Est882 has outstanding potential in bioremediation of a pyrethroid-polluted environment. These characteristics endow Est882 with potential values in various industrial applications and hydrolysis of pyrethroid residues.

Taking Advantage of Promiscuity of Cold-Active Enzymes

Cold-active enzymes increase their catalytic efficiency at low-temperature, introducing structural flexibility at or near the active sites. Inevitably, this feat seems to be accompanied by lower thermal stability. These characteristics have made cold-active enzymes into attractive targets for the industrial applications, since they could reduce the energy cost in the reaction, attenuate side-reactions, and simply be inactivated. In addition, the increased structural flexibility could result in broad substrate specificity for various non-native substrates, which is called substrate promiscuity. In this perspective, we deal with a less addressed aspect of cold-active enzymes, substrate promiscuity, which has enormous potential for semi-synthesis or enzymatic modification of fine chemicals and drugs. Further structural and directed-evolutional studies on substrate promiscuity of cold-active enzymes will provide a new workhorse in white biotechnology.

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 a novel esterase from Thauera sp

A novel esterase gene TLip was identified from the strain Thauera sp. and expressed at high levels in Escherichia coli. The TLip protein shared the highest identity (48%) to esterase TesA from Pseudomonas aeruginosa when compared to enzymes with reported properties. Phylogenetic analysis showed that TLip belongs to the GDSL family of bacterial lipolytic enzymes. TLip was an alkaline esterase with a broad optimal temperature range 37-50 °C and an optimal pH of 8.0. Substrate specificity assays showed that TLip preferred medium chain p-nitrophenyl esters (C₆ -C₁₂ ). Besides, the activity of TLip was strongly inhibited by Cu²⁺ but greatly enhanced by Triton X-100 and Tween 80. Thermostability assay revealed that TLip was stable without loss of activity at 37 °C and still retained 69% activity at 50 °C after 2 H of incubation. Together, these provided a good candidate for further exploration of TLip as a promising biocatalyst in industry.

A novel acetyl xylan esterase enabling complete deacetylation of substituted xylans

BACKGROUND

Acetylated 4-O-(methyl)glucuronoxylan (GX) is the main hemicellulose in deciduous hardwood, and comprises a β-(1→4)-linked xylopyranosyl (Xylp) backbone substituted by both acetyl groups and α-(1→2)-linked 4-O-methylglucopyranosyluronic acid (MeGlcpA). Whereas enzymes that target singly acetylated Xylp or doubly 2,3-O-acetyl-Xylp have been well characterized, those targeting (2-O-MeGlcpA)3-O-acetyl-Xylp structures in glucuronoxylan have remained elusive.

RESULTS

An unclassified carbohydrate esterase (FjoAcXE) was identified as a protein of unknown function from a polysaccharide utilization locus (PUL) otherwise comprising carbohydrate-active enzyme families known to target xylan. FjoAcXE was shown to efficiently release acetyl groups from internal (2-O-MeGlcpA)3-O-acetyl-Xylp structures, an activity that has been sought after but lacking in known carbohydrate esterases. FjoAcXE action boosted the activity of α-glucuronidases from families GH67 and GH115 by five and nine times, respectively. Moreover, FjoAcXE activity was not only restricted to GX, but also deacetylated (3-O-Araf)2-O-acetyl-Xylp of feruloylated xylooligomers, confirming the broad substrate range of this new carbohydrate esterase.

CONCLUSION

This study reports the discovery and characterization of the novel carbohydrate esterase, FjoAcXE. In addition to cleaving singly acetylated Xylp, and doubly 2,3-O-acetyl-Xylp, FjoAcXE efficiently cleaves internal 3-O-acetyl-Xylp linkages in (2-O-MeGlcpA)3-O-acetyl-Xylp residues along with densely substituted and branched xylooligomers; activities that until now were missing from the arsenal of enzymes required for xylan conversion.

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.

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.

Structural and Biochemical Characterization of an Octameric Carbohydrate Acetylesterase from Sinorhizobium meliloti

Carbohydrate acetylesterases, which have a highly specific role among plant-interacting bacterial species, remove the acetyl groups from plant carbohydrates. Here, we determined the crystal structure of Est24, an octameric carbohydrate acetylesterase from Sinorhizobium meliloti, at 1.45 Å resolution and investigated its biochemical properties. The structure of Est24 consisted of five parallel β strands flanked by α helices, which formed an octameric assembly with two distinct interfaces. The deacetylation activity of Est24 and its mutants around the substrate-binding pocket was investigated using several substrates, including glucose pentaacetate and acetyl alginate. Elucidation of the structure-function relationships of Est24 could provide valuable opportunities for biotechnological explorations.

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

Deacetylation of 7-aminocephalosporanic acid (7-ACA) at position C-3 provides valuable starting material for producing semisynthetic β-lactam antibiotics. However, few enzymes have been characterized in this process before now. Comparative analysis of the genome of the thermophilic bacterium Alicyclobacillus tengchongensis revealed a hypothetical protein (EstD1) with typical esterase features. The EstD1 protein was functionally cloned, expressed, and purified from Escherichia coli BL21(DE3). It indeed displayed esterase activity, with optimal activity at around 65°C and pH 8.5, with a preference for esters with short-chain acyl esters (C2 to C4). Sequence alignment revealed that EstD1 is an SGNH hydrolase with the putative catalytic triad Ser15, Asp191, and His194, which belongs to carbohydrate esterase family 12. EstD1 can hydrolyze acetate at the C-3 position of 7-aminocephalosporanic acid (7-ACA) to form deacetyl-7-ACA, which is an important starting material for producing semisynthetic β-lactam antibiotics. EstD1 retained more than 50% of its initial activity when incubated at pH values ranging from 4 to 11 at 65°C for 1 h. To the best of our knowledge, this enzyme is a new SGNH hydrolase identified from thermophiles that is able to hydrolyze 7-ACA.

IMPORTANCE

Deacetyl cephalosporins are highly valuable building blocks for the industrial production of various kinds of semisynthetic β-lactam antibiotics. These compounds are derived mainly from 7-ACA, which is obtained by chemical or enzymatic processes from cephalosporin C. Enzymatic transformation of 7-ACA is the main method because of the adverse effects chemical deacylation brought to the environment. SGNH hydrolases are widely distributed in plants. However, the tools for identifying and characterizing SGNH hydrolases from bacteria, especially from thermophiles, are rather limited. Here, our work demonstrates that EstD1 belongs to the SGNH family and can hydrolyze acetate at the C-3 position of 7-ACA. Moreover, this study can enrich our understanding of the functions of these enzymes from this family.

Preparation of cobalt nanoparticles from polymorphic bacterial templates: A novel platform for biocatalysis

Nanoparticles have gathered significant research attention as materials for enzyme immobilization due to their advantageous properties such as low diffusion rates, ease of manipulation, and large surface areas. Here, polymorphic cobalt nanoparticles of varied sizes and shapes were prepared using Micrococcus lylae, Bacillus subtilis, Escherichia coli, Paracoccus sp., and Haloarcula vallismortis as bacterial templates. Furthermore, nine lipases/carboxylesterases were successfully immobilized on these cobalt nanoparticles. Especially, immobilized forms of Est-Y29, LmH, and Sm23 were characterized in more detail for potential industrial applications. Immobilization of enzymes onto cobalt oxide nanoparticles prepared from polymorphic bacterial templates may have potential for efficient hydrolysis on an industrial-scale, with several advantages such as high retention of enzymatic activity, increased stability, and strong reusability.

Identification, characterization, and immobilization of an organic solvent-stable alkaline hydrolase (PA27) from Pseudomonas aeruginosa MH38

An organic solvent-stable alkaline hydrolase (PA27) from Pseudomonas aeruginosa MH38 was expressed, characterized, and immobilized for biotechnological applications. Recombinant PA27 was expressed in Escherichia coli as a 27 kDa soluble protein and was purified by standard procedures. PA27 was found to be stable at pH 8–11 and below 50 °C. It maintained more than 80% of its activity under alkaline conditions (pH 8.0–11.0). Furthermore, PA27 exhibited remarkable stability in benzene and n-hexane at concentrations of 30% and 50%. Based on these properties, immobilization of PA27 for biotechnological applications was explored. Scanning electron microscopy revealed a very smooth spherical structure with numerous large pores. Interestingly, immobilized PA27 displayed improved thermal/chemical stabilities and high reusability. Specifically, immobilized PA27 has improved thermal stability, maintaining over 90% of initial activity after 1 h of incubation at 80 °C, whereas free PA27 had only 35% residual activity. Furthermore, immobilized PA27 showed higher residual activity than the free enzyme biocatalysts against detergents, urea, and phenol. Immobilized PA27 could be recycled 20 times with retention of ~60% of its initial activity. Furthermore, macroscopic hydrogel formation of PA27 was also investigated. These characteristics make PA27 a great candidate for an industrial biocatalyst with potential applications.

Crystallization and preliminary X-ray analysis of a highly stable novel SGNH hydrolase (Est24) from Sinorhizobium meliloti

The SGNH hydrolase family includes enzymes that catalyze the hydrolysis of a broad range of substrates. Here, the crystallization and preliminary X-ray crystallographic studies of a novel SGNH hydrolase (Est24) from Sinorhizobium meliloti were performed. Recombinant Est24 protein containing an N-terminal His tag was expressed in Escherichia coli and purified to homogeneity. Est24 was then crystallized using a solution consisting of 0.2 M ammonium phosphate pH 4.6, 20% polyethylene glycol 3350. X-ray diffraction data were collected to a resolution of 1.45 Å with an R(merge) of 9.4%. The Est24 crystals belonged to space group C2, with unit-cell parameters a = 129.09, b = 88.63, c = 86.15 Å, α = 90.00, β = 114.30, γ = 90.00°. A molecular-replacement solution was obtained using the crystal structure of Mycobacterium smegmatis arylesterase as a template and structure refinement of Est24 is in progress.

Identification, characterization, and application of a virulence factor (EfEstA) from Enterococcus faecalis

Although virulence factors from pathogenic bacteria have been proposed as promising industrial enzymes, characterization and application of these enzymes have been still unexplored. The objective of this study was to identify and characterize virulence factors from pathogenic bacteria for industrial applications. Here, a virulence factor (EfEstA) from Enterococcus faecalis was identified and characterized using SDS-PAGE, enzyme assays, and molecular modeling. In addition, it has been shown that cross-linked enzyme aggregates (CLEAs) of EfEstA exhibited improved stabilities and high recycling activities compared to free EfEstA. These characteristics of EfEstA shed light on the design of new lipase-based systems for industrial applications.