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Special Issue "Microbial Enzymes and Metabolites"

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

Deadline for manuscript submissions: 31 October 2021.

Special Issue Editor

Prof. Dr. Georg A. Sprenger
E-Mail Website
Guest Editor
Institute of Microbiology, University of Stuttgart, Stuttgart, Germany
Interests: carbon-carbon (C-C) bonding enzymes; amino acid biosynthesis; metabolic engineering
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

This issue of IJMS will be devoted to microbial enzymes and metabolites. Microorganisms host a plentitude of enzymes. Microbial enzymes play roles in specific biosynthetic and catabolic pathways. They are being used in vitro for diagnostic purposes, for the production of low-molecular-weight compounds (amino acids, peptides, organic acids, alcohols, antibiotics, sugars), in the production of biofuels a.o. Microbial enzymes have already become standard tools in bio-organic and pharmaceutical chemistry, as they enlarge the toolbox for organic chemists. The study of the structure–function relationships of these enzymes (enzymatic mechanisms, substrate scope and stereoselectivity, protein design) allows us to broaden their substrate ranges. New developments in enzyme design also deal with microbial enzymes to create reactions that are new to nature. Enzyme cascades involve several enzymes to achieve novel compounds. Finally, in metabolic engineering of microorganisms, novel metabolic pathways are opened up by coupling of microbial enzymes stemming from various origins.

Prof. Dr. Georg A. Sprenger
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. International Journal of Molecular Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

  • Structure/function relationships
  • protein engineering/enzyme design
  • biocatalysis
  • metabolites

Published Papers (3 papers)

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Research

Article
Enzymatic Pretreatment with Laccases from Lentinus sajor-caju Induces Structural Modification in Lignin and Enhances the Digestibility of Tropical Forage Grass (Panicum maximum) Grown under Future Climate Conditions
Int. J. Mol. Sci. 2021, 22(17), 9445; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms22179445 - 31 Aug 2021
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Abstract
Since laccase acts specifically in lignin, the major contributor to biomass recalcitrance, this biocatalyst represents an important alternative to the pretreatment of lignocellulosic biomass. Therefore, this study investigates the laccase pretreatment and climate change effects on the hydrolytic performance of Panicum maximum. Through [...] Read more.
Since laccase acts specifically in lignin, the major contributor to biomass recalcitrance, this biocatalyst represents an important alternative to the pretreatment of lignocellulosic biomass. Therefore, this study investigates the laccase pretreatment and climate change effects on the hydrolytic performance of Panicum maximum. Through a Trop-T-FACE system, P. maximum grew under current (Control (C)) and future climate conditions: elevated temperature (2 °C more than the ambient canopy temperature) combined with elevated atmospheric CO2 concentration(600 μmol mol−1), name as eT+eC. Pretreatment using a laccase-rich crude extract from Lentinus sajor caju was optimized through statistical strategies, resulting in an increase in the sugar yield of P. maximum biomass (up to 57%) comparing to non-treated biomass and enabling hydrolysis at higher solid loading, achieving up to 26 g L−1. These increments are related to lignin removal (up to 46%) and lignin hydrophilization catalyzed by laccase. Results from SEM, CLSM, FTIR, and GC-MS supported the laccase-catalyzed lignin removal. Moreover, laccase mitigates climate effects, and no significant differences in hydrolytic potential were found between C and eT+eC groups. This study shows that crude laccase pretreatment is a potential and sustainable method for biorefinery solutions and helped establish P. maximum as a promising energy crop. Full article
(This article belongs to the Special Issue Microbial Enzymes and Metabolites)
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Article
Opening a Novel Biosynthetic Pathway to Dihydroxyacetone and Glycerol in Escherichia coli Mutants through Expression of a Gene Variant (fsaAA129S) for Fructose 6-Phosphate Aldolase
Int. J. Mol. Sci. 2020, 21(24), 9625; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21249625 - 17 Dec 2020
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Abstract
Phosphofructokinase (PFK) plays a pivotal role in glycolysis. By deletion of the genes pfkA, pfkB (encoding the two PFK isoenzymes), and zwf (glucose 6-phosphate dehydrogenase) in Escherichia coli K-12, a mutant strain (GL3) with a complete block in glucose catabolism was created. [...] Read more.
Phosphofructokinase (PFK) plays a pivotal role in glycolysis. By deletion of the genes pfkA, pfkB (encoding the two PFK isoenzymes), and zwf (glucose 6-phosphate dehydrogenase) in Escherichia coli K-12, a mutant strain (GL3) with a complete block in glucose catabolism was created. Introduction of plasmid-borne copies of the fsaA wild type gene (encoding E. coli fructose 6-phosphate aldolase, FSAA) did not allow a bypass by splitting fructose 6-phosphate (F6P) into dihydroxyacetone (DHA) and glyceraldehyde 3-phosphate (G3P). Although FSAA enzyme activity was detected, growth on glucose was not reestablished. A mutant allele encoding for FSAA with an amino acid exchange (Ala129Ser) which showed increased catalytic efficiency for F6P, allowed growth on glucose with a µ of about 0.12 h−1. A GL3 derivative with a chromosomally integrated copy of fsaAA129S (GL4) grew with 0.05 h−1 on glucose. A mutant strain from GL4 where dhaKLM genes were deleted (GL5) excreted DHA. By deletion of the gene glpK (glycerol kinase) and overexpression of gldA (of glycerol dehydrogenase), a strain (GL7) was created which showed glycerol formation (21.8 mM; yield approximately 70% of the theoretically maximal value) as main end product when grown on glucose. A new-to-nature pathway from glucose to glycerol was created. Full article
(This article belongs to the Special Issue Microbial Enzymes and Metabolites)
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Article
Assessing the Thiamine Diphosphate Dependent Pyruvate Dehydrogenase E1 Subunit for Carboligation Reactions with Aliphatic Ketoacids
Int. J. Mol. Sci. 2020, 21(22), 8641; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms21228641 - 16 Nov 2020
Cited by 1 | Viewed by 798
Abstract
The synthetic properties of the Thiamine diphosphate (ThDP)-dependent pyruvate dehydrogenase E1 subunit from Escherichia coli (EcPDH E1) was assessed for carboligation reactions with aliphatic ketoacids. Due to its role in metabolism, EcPDH E1 was previously characterised with respect to its [...] Read more.
The synthetic properties of the Thiamine diphosphate (ThDP)-dependent pyruvate dehydrogenase E1 subunit from Escherichia coli (EcPDH E1) was assessed for carboligation reactions with aliphatic ketoacids. Due to its role in metabolism, EcPDH E1 was previously characterised with respect to its biochemical properties, but it was never applied for synthetic purposes. Here, we show that EcPDH E1 is a promising biocatalyst for the production of chiral α-hydroxyketones. WT EcPDH E1 shows a 180–250-fold higher catalytic efficiency towards 2-oxobutyrate or pyruvate, respectively, in comparison to engineered transketolase variants from Geobacillus stearothermophilus (TKGST). Its broad active site cleft allows for the efficient conversion of both (R)- and (S)-configured α-hydroxyaldehydes, next to linear and branched aliphatic aldehydes as acceptor substrates under kinetically controlled conditions. The alternate, thermodynamically controlled self-reaction of aliphatic aldehydes was shown to be limited to low levels of conversion, which we propose to be due to their large hydration constants. Additionally, the thermodynamically controlled approach was demonstrated to suffer from a loss of stereoselectivity, which makes it unfeasible for aliphatic substrates. Full article
(This article belongs to the Special Issue Microbial Enzymes and Metabolites)
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