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Special Issue "Microbial Enzymes"

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Biochemistry".

Deadline for manuscript submissions: closed (30 November 2018).

Special Issue Editors

Prof. Dr. Arnold L. Demain
Website
Guest Editor
Research Institute for Scientists Emeriti (RISE), Drew University, Madison, NJ 07940, USA
Interests: industrial microbiology; biotechnology; microbial fermentation; antibiotics; enzymes; secondary metabolism; biofuels; bioconversions
Prof. Dr. Lonnie Ingram
Website
Guest Editor
Professor Emeritus of Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, USA
Interests: genetic engineering; industrial fermentation processes; carbohydrate metabolism; expression and secretion of glycohydrolases which degrade plant polymers; alcohol tolerance

Special Issue Information

Dear Colleagues,

There are six major classes of microbial enzymes: Hydrolases, isomerases, ligases, lyases, oxidoreductases, and transferases. They have very important applications as catalysts, e.g., elimination of extreme pH values, high temperatures, and use of organic solvents. They offer product purity, ease of termination of activity, reduced environmental impact, high substrate specificity and low toxicity. Microbes are the main sources of enzymes, since they produce high concentrations of extracellular enzymes. Microbial enzymes have unique properties including high specificity, high yields, rapid action, biodegradability, ability to act under mild conditions, and reduction in generation of waste materials. The most important enzymes include those used for (a) feeding of poultry and swine, e.g., proteases, phytases, glucanases, alpha-galactosidases, alpha-amylases, and polygalacturonases; and (b) food and beverage manufacture, e.g., lipases, proteases, oxidases, amylases, peroxidases and cellulases. This Special Issue will offer a platform for high-quality publications on microbial enzymes, leading to a better understanding of the functional properties of industrial enzymes.

Prof. Dr. Arnold L.  Demain
Prof. Dr. Lonnie Ingram
Guest Editor

Manuscript Submission Information

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Keywords

  • Microbial enzymes
  • Extracellular enzymes
  • Technical enzymes
  • High specificity
  • High yields
  • Rapid action
  • Biodegradability

Published Papers (14 papers)

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Research

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Open AccessArticle
An Acid Up-Regulated Surface Protein of Lactobacillus paracasei Strain GCRL 46 is Phylogenetically Related to the Secreted Glucan- (GpbB) and Immunoglobulin-Binding (SibA) Protein of Pathogenic Streptococci
Int. J. Mol. Sci. 2019, 20(7), 1610; https://doi.org/10.3390/ijms20071610 - 31 Mar 2019
Cited by 1
Abstract
Bacterial cell wall hydrolases, including amidases and peptidases, play a critical role in peptidoglycan turnover during growth, impacting daughter cell separation, and cell death, through autolysis. When exploring the regulation of protein expression across the growth cycle of an acid-resistant strain of Lactobacillus [...] Read more.
Bacterial cell wall hydrolases, including amidases and peptidases, play a critical role in peptidoglycan turnover during growth, impacting daughter cell separation, and cell death, through autolysis. When exploring the regulation of protein expression across the growth cycle of an acid-resistant strain of Lactobacillus paracasei, GCRL 46, we observed temporal up-regulation of proteins in the 40–45 kDa molecular weight range for whole-cell extracts when culturing in fermenters at a controlled pH of 4.0 versus optimum growth pH of 6.3. Up-regulation of proteins in this size range was not detected in SDS-PAGE gels of the cytosolic fraction, but was routinely detected following growth at low pH in whole cells and cell debris obtained after bead beating and centrifugation, indicating a cell surface location. N-terminal sequencing and in silico analyses showed sequence similarity with proteins in the L. casei group (L. casei, L. paracasei and L. rhamnosus) which were variously annotated as uncharacterized proteins, surface antigens, possible TrsG proteins, CHAP (cysteine, histidine-dependent amidohydrolases/peptidases)-domain proteins or putative peptidoglycan d,l-endopeptidase due to the presence of a CwlO domain. This protein is a homologue of the p40 (Msp2) secreted protein of L. rhamnosus LGG, which is linked to probiotic functionality in this species, and is phylogenetically related to structurally-similar proteins found in Enterococcus, Streptococcus and Bifidobacterium species, including the glucan-binding (GbpB), surface antigen (SagA) proteins detected in pathogenic group A streptococci species as secreted, immunoglobulin-binding (SibA) proteins (also named PcsB). Three-dimensional (3D) modelling predicted structural similarities in the CHAP proteins from the L. casei group and streptococcal species, indicating retention of overall architecture despite sequence divergence, and an implied retention of function during evolution. A phylogenetically-related hydrolase also contained the CwlO domain with a NLPC_P60 domain, and showed similar overall but distinct architecture to the CHAP proteins. We concluded that the surface-located, CHAP protein in L. casei is up-regulated during long-term exposure to acidic conditions during growth but not during acid shock. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
A Thermostable Monoacylglycerol Lipase from Marine Geobacillus sp. 12AMOR1: Biochemical Characterization and Mutagenesis Study
Int. J. Mol. Sci. 2019, 20(3), 780; https://doi.org/10.3390/ijms20030780 - 12 Feb 2019
Cited by 11
Abstract
Lipases with unique substrate specificity are highly desired in biotechnological applications. In this study, a putative marine Geobacillus sp. monoacylglycerol lipase (GMGL) encoded gene was identified by a genomic mining strategy. The gene was expressed in Escherichia coli as a His-tag fusion protein [...] Read more.
Lipases with unique substrate specificity are highly desired in biotechnological applications. In this study, a putative marine Geobacillus sp. monoacylglycerol lipase (GMGL) encoded gene was identified by a genomic mining strategy. The gene was expressed in Escherichia coli as a His-tag fusion protein and purified by affinity chromatography with a yield of 264 mg per liter fermentation broth. The recombinant GMGL shows the highest hydrolysis activity at 60 °C and pH 8.0, and the half-life was 60 min at 70 °C. The GMGL is active on monoacylglycerol (MAG) substrate but not diacylglycerol (DAG) or triacylglycerol (TAG), and produces MAG as the single product in the esterification reaction. Modeling structure analysis showed that the catalytic triad is formed by Ser97, Asp196 and His226, and the flexible cap region is constituted by residues from Ala120 to Thr160. A mutagenesis study on Leu142, Ile145 and Ile170 located in the substrate binding tunnel revealed that these residues were related with its substrate specificity. The kcat/Km value toward the pNP-C6 substrate in mutants Leu142Ala, Ile145Ala and Ile170Phe increased to 2.3-, 1.4- and 2.2-fold as compared to that of the wild type, respectively. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
RNA Sequencing Reveals Differential Gene Expression of Cerrena Unicolor in Response to Variable Lighting Conditions
Int. J. Mol. Sci. 2019, 20(2), 290; https://doi.org/10.3390/ijms20020290 - 12 Jan 2019
Cited by 6
Abstract
To elucidate the light-dependent gene expression in Cerrena unicolor FCL139, the transcriptomes of the fungus growing in white, blue, green, and red lighting conditions and darkness were analysed. Among 10,413 all-unigenes detected in C. unicolor, 7762 were found to be expressed in [...] Read more.
To elucidate the light-dependent gene expression in Cerrena unicolor FCL139, the transcriptomes of the fungus growing in white, blue, green, and red lighting conditions and darkness were analysed. Among 10,413 all-unigenes detected in C. unicolor, 7762 were found to be expressed in all tested conditions. Transcripts encoding putative fungal photoreceptors in the C. unicolor transcriptome were identified. The number of transcripts uniquely produced by fungus ranged from 20 during its growth in darkness to 112 in the green lighting conditions. We identified numerous genes whose expression differed substantially between the darkness (control) and each of the light variants tested, with the greatest number of differentially expressed genes (DEGs) (454 up- and 457 down-regulated) observed for the white lighting conditions. The DEGs comprised those involved in primary carbohydrate metabolism, amino acid metabolism, autophagy, nucleotide repair systems, signalling pathways, and carotenoid metabolism as defined using Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The analysis of the expression profile of genes coding for lignocellulose-degrading enzymes suggests that the wood-degradation properties of C. unicolor may be independent of the lighting conditions and may result from the overall stimulation of fungal metabolism by daylight. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
Uridine Diphosphate-Dependent Glycosyltransferases from Bacillus subtilis ATCC 6633 Catalyze the 15-O-Glycosylation of Ganoderic Acid A
Int. J. Mol. Sci. 2018, 19(11), 3469; https://doi.org/10.3390/ijms19113469 - 05 Nov 2018
Cited by 7
Abstract
Bacillus subtilis ATCC (American type culture collection) 6633 was found to biotransform ganoderic acid A (GAA), which is a major lanostane triterpenoid from the medicinal fungus Ganoderma lucidum. Five glycosyltransferase family 1 (GT1) genes of this bacterium, including two uridine diphosphate-dependent glycosyltransferase [...] Read more.
Bacillus subtilis ATCC (American type culture collection) 6633 was found to biotransform ganoderic acid A (GAA), which is a major lanostane triterpenoid from the medicinal fungus Ganoderma lucidum. Five glycosyltransferase family 1 (GT1) genes of this bacterium, including two uridine diphosphate-dependent glycosyltransferase (UGT) genes, BsUGT398 and BsUGT489, were cloned and overexpressed in Escherichia coli. Ultra-performance liquid chromatography confirmed the two purified UGT proteins biotransform ganoderic acid A into a metabolite, while the other three purified GT1 proteins cannot biotransform GAA. The optimal enzyme activities of BsUGT398 and BsUGT489 were at pH 8.0 with 10 mM of magnesium or calcium ion. In addition, no candidates showed biotransformation activity toward antcin K, which is a major ergostane triterpenoid from the fruiting bodies of Antrodia cinnamomea. One biotransformed metabolite from each BsUGT enzyme was then isolated with preparative high-performance liquid chromatography. The isolated metabolite from each BsUGT was identified as ganoderic acid A-15-O-β-glucoside by mass and nuclear magnetic resonance spectroscopy. The two BsUGTs in the present study are the first identified enzymes that catalyze the 15-O-glycosylation of triterpenoids. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
Directed Evolution of a Homodimeric Laccase from Cerrena unicolor BBP6 by Random Mutagenesis and In Vivo Assembly
Int. J. Mol. Sci. 2018, 19(10), 2989; https://doi.org/10.3390/ijms19102989 - 30 Sep 2018
Cited by 4
Abstract
Laccases have great potential for industrial applications due to their green catalytic properties and broad substrate specificities, and various studies have attempted to improve the catalytic performance of these enzymes. Here, to the best of our knowledge, we firstly report the directed evolution [...] Read more.
Laccases have great potential for industrial applications due to their green catalytic properties and broad substrate specificities, and various studies have attempted to improve the catalytic performance of these enzymes. Here, to the best of our knowledge, we firstly report the directed evolution of a homodimeric laccase from Cerrena unicolor BBP6 fused with α-factor prepro-leader that was engineered through random mutagenesis followed by in vivo assembly in Saccharomyces cerevisiae. Three evolved fusion variants selected from ~3500 clones presented 31- to 37-fold increases in total laccase activity, with better thermostability and broader pH profiles. The evolved α-factor prepro-leader enhanced laccase expression levels by up to 2.4-fold. Protein model analysis of these variants reveals that the beneficial mutations have influences on protein pKa shift, subunit interaction, substrate entrance, and C-terminal function. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
Effect of N- and C-Terminal Amino Acids on the Interfacial Binding Properties of Phospholipase D from Vibrio parahaemolyticus
Int. J. Mol. Sci. 2018, 19(8), 2447; https://doi.org/10.3390/ijms19082447 - 19 Aug 2018
Abstract
The effects of N-terminal (1–34 amino acids) and C-terminal (434–487 amino acids) amino acid sequences on the interfacial binding properties of Phospholipase D from Vibrio parahaemolyticus (VpPLD) were characterized by using monomolecular film technology. Online tools allowed the prediction of the secondary structure [...] Read more.
The effects of N-terminal (1–34 amino acids) and C-terminal (434–487 amino acids) amino acid sequences on the interfacial binding properties of Phospholipase D from Vibrio parahaemolyticus (VpPLD) were characterized by using monomolecular film technology. Online tools allowed the prediction of the secondary structure of the target N- and C-terminal VpPLD sequences. Various truncated forms of VpPLD with different N- or C-terminal deletions were designed, based on their secondary structure, and their membrane binding properties were examined. The analysis of the maximum insertion pressure (MIP) and synergy factor “a” indicated that the loop structure (1–25 amino acids) in the N-terminal segment of VpPLD had a positive effect on the binding of VpPLD to phospholipid monolayers, especially to 1,2-dimyristoyl-sn-glycero-3-phosphoserine and 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The deletion affecting the N-terminus loop structure caused a significant decrease of the MIP and synergy factor a of the protein for these phospholipid monolayers. Conversely, the deletion of the helix structure (26–34 amino acids) basically had no influence on the binding of VpPLD to phospholipid monolayers. The deletion of the C-terminal amino acids 434–487 did not significantly change the binding selectivity of VpPLD for the various phospholipid monolayer tested here. However, a significant increase of the MIP value for all the phospholipid monolayers strongly indicated that the three-strand segment (434–469 amino acids) had a great negative effect on the interfacial binding to these phospholipid monolayers. The deletion of this peptide caused a significantly greater insertion of the protein into the phospholipid monolayers examined. The present study provides detailed information on the effect of the N- and C-terminal segments of VpPLD on the interfacial binding properties of the enzyme and improves our understanding of the interactions between this enzyme and cell membranes. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
Genome Sequencing and Carbohydrate-Active Enzyme (CAZyme) Repertoire of the White Rot Fungus Flammulina elastica
Int. J. Mol. Sci. 2018, 19(8), 2379; https://doi.org/10.3390/ijms19082379 - 13 Aug 2018
Cited by 13
Abstract
Next-generation sequencing (NGS) of the Flammulina elastica (wood-rotting basidiomycete) genome was performed to identify carbohydrate-active enzymes (CAZymes). The resulting assembly (31 kmer) revealed a total length of 35,045,521 bp (49.7% GC content). Using the AUGUSTUS tool, 12,536 total gene structures were predicted by [...] Read more.
Next-generation sequencing (NGS) of the Flammulina elastica (wood-rotting basidiomycete) genome was performed to identify carbohydrate-active enzymes (CAZymes). The resulting assembly (31 kmer) revealed a total length of 35,045,521 bp (49.7% GC content). Using the AUGUSTUS tool, 12,536 total gene structures were predicted by ab initio gene prediction. An analysis of orthologs revealed that 6806 groups contained at least one F. elastica protein. Among the 12,536 predicted genes, F. elastica contained 24 species-specific genes, of which 17 genes were paralogous. CAZymes are divided into five classes: glycoside hydrolases (GHs), carbohydrate esterases (CEs), polysaccharide lyases (PLs), glycosyltransferases (GTs), and auxiliary activities (AA). In the present study, annotation of the predicted amino acid sequences from F. elastica genes using the dbCAN CAZyme database revealed 508 CAZymes, including 82 AAs, 218 GHs, 89 GTs, 18 PLs, 59 CEs, and 42 carbohydrate binding modules in the F. elastica genome. Although the CAZyme repertoire of F. elastica was similar to those of other fungal species, the total number of GTs in F. elastica was larger than those of other basidiomycetes. This genome information elucidates newly identified wood-degrading machinery in F. elastica, offers opportunities to better understand this fungus, and presents possibilities for more detailed studies on lignocellulosic biomass degradation that may lead to future biotechnological and industrial applications. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
An Organic Solvent-Tolerant Lipase with Both Hydrolytic and Synthetic Activities from the Oleaginous Fungus Mortierella echinosphaera
Int. J. Mol. Sci. 2018, 19(4), 1129; https://doi.org/10.3390/ijms19041129 - 10 Apr 2018
Cited by 2
Abstract
Lipase enzymes of the oleaginous fungal group Mortierella are rarely studied. However, considering that most commercial lipases are derived from filamentous fungal sources, their investigation can contribute to the cost-effective development of new biotechnological processes. Here, an extracellular lipase with a molecular mass [...] Read more.
Lipase enzymes of the oleaginous fungal group Mortierella are rarely studied. However, considering that most commercial lipases are derived from filamentous fungal sources, their investigation can contribute to the cost-effective development of new biotechnological processes. Here, an extracellular lipase with a molecular mass of 30 kDa was isolated from Mortierella echinosphaera CBS 575.75 and characterized. The purified lipase exhibited an optimal p-nitrophenyl palmitate (pNPP)-hydrolyzing activity at 25 °C and pH 6.6–7.0 and proved to be highly stable at temperatures up to 40 °C and under broad pH conditions. The enzyme was active under low temperatures, retaining 32.5% of its activity at 10 °C, and was significantly stable in polar and non-polar organic solvents. The Km, Vmax, and kcat for pNPP were 0.336 mM, 30.4 μM/min, and 45.7 1/min for pNPP and 0.333 mM, 36.9 μM/min, and 55.6 1/min for pNP-decanoate, respectively. The pNPP hydrolysis was inhibited by Hg2+, N-bromosuccinimide, and sodium dodecyl sulfate, while ethylenediaminetetraacetic acid and metal ions, such as Ca2+, Mg2+, Na+, and K+ enhanced the activity. The purified lipase had non-regioselective activity and wide substrate specificity, showing a clear preference for medium-chained p-nitrophenyl esters. Besides its good transesterification activity, the enzyme appeared as a suitable biocatalyst to operate selective esterification reactions to long-chained alkyl esters. Adsorption to Accurel MP1000 improved the storage stability of the enzyme at 5 °C. The immobilized lipase displayed tolerance to a non-aqueous environment and was reusable for up to five cycles without significant loss in its synthetic and hydrolytic activities. These findings confirm the applicability of both the free and the immobilized enzyme preparations in future research. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
The Effect of N-Terminal Domain Removal towards the Biochemical and Structural Features of a Thermotolerant Lipase from an Antarctic Pseudomonas sp. Strain AMS3
Int. J. Mol. Sci. 2018, 19(2), 560; https://doi.org/10.3390/ijms19020560 - 13 Feb 2018
Cited by 8
Abstract
Lipase plays an important role in industrial and biotechnological applications. Lipases have been subject to modification at the N and C terminals, allowing better understanding of lipase stability and the discovery of novel properties. A thermotolerant lipase has been isolated from Antarctic Pseudomonas [...] Read more.
Lipase plays an important role in industrial and biotechnological applications. Lipases have been subject to modification at the N and C terminals, allowing better understanding of lipase stability and the discovery of novel properties. A thermotolerant lipase has been isolated from Antarctic Pseudomonas sp. The purified Antarctic AMS3 lipase (native) was found to be stable across a broad range of temperatures and pH levels. The lipase has a partial Glutathione-S-transferase type C (GST-C) domain at the N-terminal not found in other lipases. To understand the influence of N-terminal GST-C domain on the biochemical and structural features of the native lipase, the deletion of the GST-C domain was carried out. The truncated protein was successfully expressed in E. coli BL21(DE3). The molecular weight of truncated AMS3 lipase was approximately ~45 kDa. The number of truncated AMS3 lipase purification folds was higher than native lipase. Various mono and divalent metal ions increased the activity of the AMS3 lipase. The truncated AMS3 lipase demonstrated a similarly broad temperature range, with the pH profile exhibiting higher activity under alkaline conditions. The purified lipase showed a substrate preference for a long carbon chain substrate. In addition, the enzyme activity in organic solvents was enhanced, especially for toluene, Dimethylsulfoxide (DMSO), chloroform and xylene. Molecular simulation revealed that the truncated lipase had increased structural compactness and rigidity as compared to native lipase. Removal of the N terminal GST-C generally improved the lipase biochemical characteristics. This enzyme may be utilized for industrial purposes. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
Lasiodiplodia theobromae as a Producer of Biotechnologically Relevant Enzymes
Int. J. Mol. Sci. 2018, 19(2), 29; https://doi.org/10.3390/ijms19020029 - 23 Jan 2018
Cited by 12
Abstract
Phytopathogenic fungi are known to produce several types of enzymes usually involved in plant cell wall degradation and pathogenesis. The increasing of global temperature may induce fungi, such as Lasiodiplodia theobromae (L. theobromae), to alter its behavior. Nonetheless, there is only [...] Read more.
Phytopathogenic fungi are known to produce several types of enzymes usually involved in plant cell wall degradation and pathogenesis. The increasing of global temperature may induce fungi, such as Lasiodiplodia theobromae (L. theobromae), to alter its behavior. Nonetheless, there is only limited information regarding the effect of temperature on L. theobromae production of enzymes. The need for new, thermostable enzymes, that are biotechnologically relevant, led us to investigate the effect of temperature on the production of several extracellular enzymatic activities by different L. theobromae strains. Fungi were grown at 25 °C, 30 °C and 37 °C and the enzymatic activities were detected by plate assays, quantified by spectrophotometric methods and characterized by zymography. The thermostability (25–80 °C) of the enzymes produced was also tested. Strains CAA019, CBS339.90, LA-SOL3, LA-SV1 and LA-MA-1 produced amylases, gelatinases, caseinases, cellulases, lipases, laccases, xylanases, pectinases and pectin liases. Temperature modulated the expression of the enzymes, and this effect was more visible when fungi were grown at 37 °C than at lower temperatures. Contrary to proteolytic and endoglucanolytic activities, whose highest activities were detected when fungi were grown at 30 °C, lipolytic activity was not detected at this growth temperature. Profiles of proteases and endoglucanases of fungi grown at different temperatures were characterized by zymography. Enzymes were shown to be more thermostable when fungi were grown at 30 °C. Proteases were active up to 50 °C and endoglucanases up to 70 °C. Lipases were the least stable, with activities detected up to 45 °C. The enzymatic profiles detected for L. theobromae strains tested showed to be temperature and strain-dependent, making this species a good target for biotechnological applications. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
Directed Evolution of Recombinant C-Terminal Truncated Staphylococcus epidermidis Lipase AT2 for the Enhancement of Thermostability
Int. J. Mol. Sci. 2017, 18(11), 2202; https://doi.org/10.3390/ijms18112202 - 04 Nov 2017
Cited by 9
Abstract
In the industrial processes, lipases are expected to operate at temperatures above 45 °C and could retain activity in organic solvents. Hence, a C-terminal truncated lipase from Staphylococcus epidermis AT2 (rT-M386) was engineered by directed evolution. A mutant with glycine-to-cysteine substitution (G210C) demonstrated [...] Read more.
In the industrial processes, lipases are expected to operate at temperatures above 45 °C and could retain activity in organic solvents. Hence, a C-terminal truncated lipase from Staphylococcus epidermis AT2 (rT-M386) was engineered by directed evolution. A mutant with glycine-to-cysteine substitution (G210C) demonstrated a remarkable improvement of thermostability, whereby the mutation enhanced the activity five-fold when compared to the rT-M386 at 50 °C. The rT-M386 and G210C lipases were purified concurrently using GST-affinity chromatography. The biochemical and biophysical properties of both enzymes were investigated. The G210C lipase showed a higher optimum temperature (45 °C) and displayed a more prolonged half-life in the range of 40–60 °C as compared to rT-M386. Both lipases exhibited optimal activity and stability at pH 8. The G210C showed the highest stability in the presence of polar organic solvents at 50 °C compared to the rT-M386. Denatured protein analysis presented a significant change in the molecular ellipticity value above 60 °C, which verified the experimental result on the temperature and thermostability profile of G210C. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessArticle
Molecular Docking and Screening Studies of New Natural Sortase A Inhibitors
Int. J. Mol. Sci. 2017, 18(10), 2217; https://doi.org/10.3390/ijms18102217 - 23 Oct 2017
Cited by 19
Abstract
To date, multi-drug resistant bacteria represent an increasing health threat, with a high impact on mortality, morbidity, and health costs on a global scale. The ability of bacteria to rapidly and permanently acquire new virulence factors and drug-resistance elements requires the development of [...] Read more.
To date, multi-drug resistant bacteria represent an increasing health threat, with a high impact on mortality, morbidity, and health costs on a global scale. The ability of bacteria to rapidly and permanently acquire new virulence factors and drug-resistance elements requires the development of new antimicrobial agents and selection of new proper targets, such as sortase A. This specific bacterial target plays an important role in the virulence of many Gram-positive pathogens, and its inhibition should produce a mild evolutionary pressure which will not favor the development of resistance. A primary screening using a fluorescence resonance energy transfer assay was used to experimentally evaluate the inhibitory activity of several compounds on sortase A. Using molecular docking and structure-activity relationship analyses, several lead inhibitors were identified, which were further tested for antimicrobial activity using the well diffusion test and minimum inhibitory concentration. The toxicity was assessed using the Daphnia magna test and used as a future screening filter. Three natural compounds were identified in this study as promising candidates for further development into therapeutically useful anti-infective agents that could be used to treat infections caused by multi-drug resistant bacterial pathogens which include sortase A in their enzymatic set. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Review

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Open AccessReview
The Role of Proteases in the Virulence of Plant Pathogenic Bacteria
Int. J. Mol. Sci. 2019, 20(3), 672; https://doi.org/10.3390/ijms20030672 - 04 Feb 2019
Cited by 12
Abstract
A pathogenic lifestyle is inextricably linked with the constant necessity of facing various challenges exerted by the external environment (both within and outside the host). To successfully colonize the host and establish infection, pathogens have evolved sophisticated systems to combat the host defense [...] Read more.
A pathogenic lifestyle is inextricably linked with the constant necessity of facing various challenges exerted by the external environment (both within and outside the host). To successfully colonize the host and establish infection, pathogens have evolved sophisticated systems to combat the host defense mechanisms and also to be able to withstand adverse environmental conditions. Proteases, as crucial components of these systems, are involved in a variety of processes associated with infection. In phytopathogenic bacteria, they play important regulatory roles and modulate the expression and functioning of various virulence factors. Secretory proteases directly help avoid recognition by the plant immune systems, and contribute to the deactivation of the defense response pathways. Finally, proteases are important components of protein quality control systems, and thus enable maintaining homeostasis in stressed bacterial cells. In this review, we discuss the known protease functions and protease-regulated signaling processes associated with virulence of plant pathogenic bacteria. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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Open AccessReview
Biosynthesis of Metal Nanoparticles via Microbial Enzymes: A Mechanistic Approach
Int. J. Mol. Sci. 2018, 19(12), 4100; https://doi.org/10.3390/ijms19124100 - 18 Dec 2018
Cited by 51
Abstract
During the last decade, metal nanoparticles (MtNPs) have gained immense popularity due to their characteristic physicochemical properties, as well as containing antimicrobial, anti-cancer, catalyzing, optical, electronic and magnetic properties. Primarily, these MtNPs have been synthesized through different physical and chemical methods. However, these [...] Read more.
During the last decade, metal nanoparticles (MtNPs) have gained immense popularity due to their characteristic physicochemical properties, as well as containing antimicrobial, anti-cancer, catalyzing, optical, electronic and magnetic properties. Primarily, these MtNPs have been synthesized through different physical and chemical methods. However, these conventional methods have various drawbacks, such as high energy consumption, high cost and the involvement of toxic chemical substances. Microbial flora has provided an alternative platform for the biological synthesis of MtNPs in an eco-friendly and cost effective way. In this article we have focused on various microorganisms used for the synthesis of different MtNPs. We also have elaborated on the intracellular and extracellular mechanisms of MtNP synthesis in microorganisms, and have highlighted their advantages along with their challenges. Moreover, due to several advantages over chemically synthesized nanoparticles, the microbial MtNPs, with their exclusive and dynamic characteristics, can be used in different sectors like the agriculture, medicine, cosmetics and biotechnology industries in the near future. Full article
(This article belongs to the Special Issue Microbial Enzymes)
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