Purification and properties of β-N-Acetylglucosaminidase from Vibrio alginolyticus H-8

Enzymatic properties of β-N-acetylglucosaminidases

β-N-Acetylglucosaminidases (GlcNAcases) hydrolyse N-acetylglucosamine-containing oligosaccharides and proteins. These enzymes produce N-acetylglucosamine (GlcNAc) and have a wide range of promising applications in the food, energy, and pharmaceutical industries, such as synergistic degradation of chitin with endo-chitinases and using GlcNAc to produce sialic acid, bioethanol, single-cell proteins, and pharmaceutical therapeutics. GlcNAcases also play an important role in the dynamic balance of cellular O-linked GlcNAc levels, catabolism of ganglioside storage in Tay-Sachs disease, and bacterial cell wall recycling and flagellar assembly. In view of these important biological functions and the wide range of industrial applications of GlcNAcases, this review aims to provide a better understanding of various advances for these enzymes. It focuses on enzymatic properties of GlcNAcases, including substrate specificity, catalytic activity, pH optimum, temperature optimum, thermostability, the effects of various metal ions and organic reagents, and transglycosylation.

Distinctive molecular and biochemical characteristics of a glycoside hydrolase family 20 β-N-acetylglucosaminidase and salt tolerance

Background

Enzymatic degradation of chitin has attracted substantial attention because chitin is an abundant renewable natural resource, second only to lignocellulose, and because of the promising applications of N-acetylglucosamine in the bioethanol, food and pharmaceutical industries. However, the low activity and poor tolerance to salts and N-acetylglucosamine of most reported β-N-acetylglucosaminidases limit their applications. Mining for novel enzymes from new microorganisms is one way to address this problem.

Results

A glycoside hydrolase family 20 (GH 20) β-N-acetylglucosaminidase (GlcNAcase) was identified from Microbacterium sp. HJ5 harboured in the saline soil of an abandoned salt mine and was expressed in Escherichia coli. The purified recombinant enzyme showed specific activities of 1773.1 ± 1.1 and 481.4 ± 2.3 μmol min⁻¹ mg⁻¹ towards p-nitrophenyl β-N-acetylglucosaminide and N,N'-diacetyl chitobiose, respectively, a V_max of 3097 ± 124 μmol min⁻¹ mg⁻¹ towards p-nitrophenyl β-N-acetylglucosaminide and a K_i of 14.59 mM for N-acetylglucosamine inhibition. Most metal ions and chemical reagents at final concentrations of 1.0 and 10.0 mM or 0.5 and 1.0% (v/v) had little or no effect (retaining 84.5 − 131.5% activity) on the enzyme activity. The enzyme can retain more than 53.6% activity and good stability in 3.0–20.0% (w/v) NaCl. Compared with most GlcNAcases, the activity of the enzyme is considerably higher and the tolerance to salts and N-acetylglucosamine is much better. Furthermore, the enzyme had higher proportions of aspartic acid, glutamic acid, alanine, glycine, random coils and negatively charged surfaces but lower proportions of cysteine, lysine, α-helices and positively charged surfaces than its homologs. These molecular characteristics were hypothesised as potential factors in the adaptation for salt tolerance and high activity of the GH 20 GlcNAcase.

Conclusions

Biochemical characterization revealed that the GlcNAcase had novel salt–GlcNAc tolerance and high activity. These characteristics suggest that the enzyme has versatile potential in biotechnological applications, such as bioconversion of chitin waste and the processing of marine materials and saline foods. Molecular characterization provided an understanding of the molecular–function relationships for the salt tolerance and high activity of the GH 20 GlcNAcase.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-017-0358-1) contains supplementary material, which is available to authorized users.

Impact of sources of environmental degradation on microbial community dynamics in non-polluted and metal-polluted soils

Soils are currently being degraded at an alarming rate due to increasing pressure from different sources of environmental degradation. Consequently, we carried out a 4-month microcosm experiment to measure the impact of different sources of environmental degradation (biodiversity loss, nitrogen deposition and climate change) on soil health in a non-polluted (non-degraded) and a heavily metal-polluted (degraded) soil, and to compare their responses. To this aim, we determined a variety of soil microbial properties with potential as bioindicators of soil health: basal respiration; β-glucosaminidase and protease activities; abundance (Q-PCR) of bacterial, fungal and chitinase genes; richness (PCR-DGGE) of fungal and chitinase genes. Non-polluted and metal-polluted soils showed different response microbial dynamics when subjected to sources of environmental degradation. The non-polluted soil appeared resilient to "biodiversity loss" and "climate change" treatments. The metal-polluted soil was probably already too severely affected by the presence of high levels of toxic metals to respond to other sources of stress. Our data together suggests that soil microbial activity and biomass parameters are more sensitive to the applied sources of environmental degradation, showing immediate responses of greater magnitude, while soil microbial diversity parameters do not show such variations.

Expression, purification and antibody preparation of flagellin FlaA from Vibrio alginolyticus strain HY9901

AIMS

The main aims of this study were to clone and express flagellin flaA gene from Vibrio alginolyticus strain HY9901, also to prepare mouse anti-FlaA polyclonal antibody for future pathogen or vaccine study.

METHODS AND RESULTS

The full-length flaA gene was amplified by PCR with designed primers. The open reading frame of flaA gene contains 1131 bp, and its putative protein consists of 376 amino acid residues. Alignment analysis indicated that the FlaA protein was highly conserved. SDS-PAGE indicated that the FlaA protein was successfully expressed in Escherichia coli BL21 (DE3). Then, the recombinant FlaA protein was purified by affinity chromatography, and the mouse anti-FlaA serum was produced. The expression of flaA gene was verified by various immunological methods, including western blotting, enzyme-linked immunosorbent assay (ELISA) and immunogold electron microscopy (IEM).

CONCLUSIONS

Flagellin flaA gene was cloned and identified from V. alginolyticus HY9901, the recombinant FlaA protein was expressed and purified, and high-titre FlaA protein-specific antibody was produced. Western blot analysis revealed that the prepared antiserum not only specifically react to FlaA fusion protein, but also to natural FlaA protein of V. alginolyticus. The expressed FlaA protein was demonstrated, for the first time, as the component of flagella from V. alginolyticus by IEM.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study may offer important insights into the pathogenesis of V. alginolyticus, provide a base for further studies on the diagnosis and evaluation that whether the FlaA protein could be used as an effective vaccine candidate against infection by V. alginolyticus and other Vibrio species. Additionally, the purified FlaA protein and polyclonal antibody can be used for further functional and structural studies.

Cloning and expression of the gene encoding an extracellular alkaline serine protease from Vibrio alginolyticus strain HY9901, the causative agent of vibriosis in Lutjanus erythopterus (Bloch)

A 750-bp internal fragment of the alkaline serine protease gene (asp) from the Vibrio alginolyticus strain HY9901 was amplified by polymerase chain reaction (PCR). The flanking sequences of the 5'- and 3'- ends of the asp gene were characterized by reverse and nested PCR. Sequence analysis showed that the asp gene contained an 1893-bp ORF encoding 630 amino acids. The deduced amino acid sequence of the ASP (alkaline serine protease) precursor showed significant homology with several bacterial alkaline serine proteases. Expression of the asp gene in Escherichia coli and activity tests of the ASP indicated that the N-signal peptide of the ASP precursor was essential to autocatalyse and fold correctly the enzyme to obtain activity. The purified ASP was lethal for Lutjanus erythopterus with an LD(50) of 0.25 microg protein g(-1) body weight.

Cloning and expression of gene encoding the thermostable direct hemolysin from Vibrio alginolyticus strain HY9901, the causative agent of vibriosis of crimson snapper (Lutjanus erythopterus)

AIMS

The main aims of this study were to clone and express complete open reading frame (ORF) of thermostable direct haemolysin gene (tdh) from Vibrio alginolyticus strain HY9901 in Escherichia coli, and further evaluate the virulence of expressed TDH on mouse and crimson snapper.

METHODS AND RESULTS

A 410 bp internal fragment of the tdh gene was amplified by touchdown PCR with designed primers. Then its unknown flanking sequences of the 5'- and 3'-ends were finally characterized by inverse PCR and nested PCR. Sequence analysis showed that the tdh gene contain 570 bp ORF which encoded 189 amino acids. The deduced amino acid sequence of the ORF was in significant homology with several Vibrio TDH. The product that the tdh gene expressed in E. coli was purified by Ni(2+)-IDA Sepharose affinity column. The activity of purified TDH was 4651 U mg(-1) protein by hide powder azure digestion. The lethal toxicity test showed that LD(50) values of the purified TDH were 5.68 and 8.34 microg TDH g(-1) body weight for mouse and crimson snapper, respectively.

CONCLUSIONS

The complete ORF of tdh gene was obtained by touchdown PCR, inverse PCR and nested PCR. The ORF was perfectly expressed in E. coli. The activity and toxicity assays showed that the N-terminal signal peptide was essential to autocatalyse and fold correctly to obtain the activity and toxicity in the purified TDH. The Native-PAGE analysis showed that the activated tdh gene expressed in E. coli was a dimer with two identical subunits.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates that the expressed activated TDH can produce the toxicity protein determined on mouse and fish, which will lead to better understandings of the identifying virulence factor that could be considered as a candidate antigen for vaccine and a diagnostic tool for vibriosis. Its use as an immunizing antigen might prevent the ability of V. alginolyticus to infect the marine aquatic animals, as a complementary measure to tick control and appropriate management in countries affected by vibriosis.

Cloning and sequencing of a chitinase gene from Vibrio alginolyticus H-8

A gene from Vibrio alginolyticus H-8, encoding chitinase, designated as chitinase B, was cloned by the shot-gun method using pUC118 and sequenced. The open reading frame consisted of 846 amino acids including a signal peptide. The molecular mass of the enzyme estimated based on the amino acid sequence data was 90 kDa. The N-terminal amino acid sequence of the enzyme was different from that of chitinase C1 which we had previously reported. This cloned chitinase B was considered one out of four chitinases (A, B, D, and E) which had been newly isolated from the culture broth and cell extract of V. alginolyticus H-8. The gene contained a chitin-binding domain and typical conserved regions of chitinases reported previously. The deduced amino acid sequence of the cloned chitinase B showed high sequence homology with the chitinase from V. parahaemolyticus (84% identity) and the chitinase from V. anguillarum (76.6%), but low sequence homology with the chitinase from V. harveyi (24.4%), and the chitodextrinase from V. furnissii (23.9%). Chitinase E found in cell extract is considered an intracellular chitinase which is different from chitodextrinases.