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The Mannitol Enzyme II of the Bacterial Phosphotransferase System: A Functionally Chimaeric Protein with Receptor, Transport, Kinase, and Regulatory Activities
Published in James F. Kane, Multifunctional Proteins: Catalytic/Structural and Regulatory, 2019
Milton H. Saier, John E. Leonard
Figure 1 shows the pathway for the initiation of D-mannitol catabolism in E. coli. The sugar is transported across the membrane and concomitantly phosphorylated by a PTS-mediated mechanism. In this process the phosphoryl group of phosphoenolpyruvate is transferred sequentially from phosphoenolpyruvate to Enzyme I and HPr, the two energy coupling proteins of the phosphotransferase system. Phospho-HPr then binds to the cytoplasmic surface of the Enzyme II,Mtl and free mannitol, in the extracellular medium, approaches the sugar binding site on the outer face of the enzyme. Group translocation of the sugar through the membrane corresponds to the simultaneous transport and phosphorylation of the substrate, with the release of D-mannitol-1-phosphate in the cytoplasm. The byproduct of this reaction is pyruvate. Cytoplasmic mannitol-1-phosphate is then oxidized to fructose-6-phosphate in a process catalyzed by mannitol-1-phosphate dehydrogenase in which NAD+ serves as the electron acceptor. While the general energy coupling proteins of the PTS, Enzyme I, and HPr, are coded for by the ptsl and ptsH genes, respectively, which comprise the pts operon,9,10 the Enzyme IIMtl and the mannitol-1-phosphate dehydrogenase are coded for by the mtlA and mtlD genes, respectively, which comprise the mtl operon.11,12,13 Substantial differences between the protein constituents of the PTS in the two principal organisms under study, E. coli and S. typhimurium, have not been revealed by available investigations.
Solute Translocations
Published in Lelio G. Colombetti, Biological Transport of Radiotracers, 2020
The criterion that a transported solute be in the same physical and chemical state on both sides of the dividing membrane is violated to an extent in considering transport by “group translocation”. The term38 implies that the solute appears on one side of the membrane in a form different from the other and that an enzyme has participated in the modification of its structure. The lowermost drawing in Figure 2 illustrates a hypothetical example. The substrate S is presented at one side of the membrane and transverses the barrier, but appears on the other side as its phosphorylated derivative. This illustration parallels the more complex phosphoenolpyruvate phosphotransferase system for the transport of some sugars into bacteria as described by Roseman and his co-workers.39,40 (The complete model envisions the participation of at least four proteins.) The transport of lactose by this system results in its appearance in the cell interior as lactose phosphate (with phosphoenolpyruvate being the initial phosphoryl donor). An analogous coupling of amino acid transport to a series of enzymatic (but not phosphorylating) reactions in the mammalian kidney, called the γ-glutamyl transpeptidase system, may participate in amino acid resorption from the renal tubule.41 In the latter example, the amino acid does not remain derivatized after translocation, but it nevertheless has undergone reactions forming and then cleaving a peptidyl bond with its α-amino group. Although these systems are of significant interest, transport by group translocation should not be confused with biological transport in its usual sense. Enzymatic manipulation of solute structure is not often a component part of solute translocation across biological membranes.
Factors Controlling the Microflora of the Healthy Mouth
Published in Michael J. Hill, Philip D. Marsh, Human Microbial Ecology, 2020
The caries-preventive effect of fluoride when present in the aqueous phase surrounding the tooth surface (saliva, plaque fluid) is widely used in preventive dentistry and is to a large extent responsible for the declining caries rates in many countries. Caries occurs when demineralization (dissolution of tooth minerals), caused by acids produced by plaque bacteria fermenting sugar, prevails over remineralization (deposition of calcium phosphate from saliva in demineralized areas), which takes place in the absence of acids in plaque or in the absence of plaque on the teeth. Fluoride has well established caries preventive effects by inhibition of demineralization and (mainly) by promoting remineralization. In addition, fluoride has inhibitory effects on bacterial sugar metabolism (Table 9),206–208 and these effects have been suggested to account for as much as 75% of the observed caries inhibition.209 Fluoride applications do not reduce the quantity of dental plaque, nor do they alter its microbial composition.210 Fluoride is, however, taken up by the bacteria, especially as undissociated HF at low plaque pH values. Intracellularly, HF dissociates into F− and H+, causing acidification; this process is further enhanced because fluoride also inhibits proton transport out of the bacteria.211 Fluoride and H+ ions both inhibit the glycolytic enzymes and hence acid production. Fluoride specifically inhibits enolase, leading to decreased levels of its product, phosphoenol pyruvate, PEP (Figure 26). This has the additional (and equally important) effect of inhibiting sugar uptake into the bacterium by the PEP-mediated phosphotransferase system. Therefore, sugar utilization is futher reduced, and storage of glycogen in the bacterium is also inhibited. Fluoride also reduces the aciduric (acid-tolerating) properties, which normally make it possible for streptococci to grow and ferment sugars even at low plaque pH.212 The concentration of fluoride in dental plaque bacteria and the complex interference of fluoride with bacterial metabolism (Table 9) can to a large extent explain the caries-inhibiting effect of fluoride exposure from drinking water, toothpastes, fluoride rinses, varnishes, gels, chewing tablets, and topical applications used in preventive dentistry. A major drawback with fluoride is, however, the lack of effect on plaque accumulation and on periodontal diseases.
Nicotinamide could reduce growth and cariogenic virulence of Streptococcus mutans
Published in Journal of Oral Microbiology, 2022
Yongwang Lin, Tao Gong, Qizhao Ma, Meiling Jing, Ting Zheng, Jiangchuan Yan, Jiamin Chen, Yangyang Pan, Qun Sun, Xuedong Zhou, Yuqing Li
We further conducted gene annotation enrichment of DEGs using the DAVID bioinformatics tools (http://david.abcc.ncifcrf. gov/) to gain insights into the biological effects of NAM on S. mutans. As shown in Figure 3b, the DEGs were enriched in six pathways of the Kyoto Encyclopedia of Genes and Genomes (KEGG), with seven gene ontology (GO) terms. Notably, the integral component of membrane, sugar metabolism, the phosphotransferase system, and microbial metabolism in diverse environments were enriched with downregulated genes. In contrast, GO terms, including damaged DNA binding, the arginine biosynthesis process, and the KEGG pathways, including oxocarboxylic acid metabolism and arginine biosynthesis, were significantly enriched with upregulated genes (Figure 3b, P< 0.05).
An oxidation resistant pediocin PA-1 derivative and penocin A display effective anti-Listeria activity in a model human gut environment
Published in Gut Microbes, 2022
Taís M. Kuniyoshi, Paula M. O’Connor, Elaine Lawton, Dinesh Thapa, Beatriz Mesa-Pereira, Sara Abulu, Colin Hill, R. Paul Ross, Ricardo P. S. Oliveira, Paul D. Cotter
In this study, pediocin M31L displayed similar anti-Listeria activity to native pediocin PA-1. When the antimicrobial activity of the three pediocins was assessed against Listeria in broth media, a bacteriostatic effect was observed even at higher bacteriocin concentrations. Mechanisms of bacteriocin resistance and bacteriocin tolerance are not fully studied but have been described within all classes of bacteriocin.31 Bacteriocin resistance can be both acquired and innate, and the main resistance mechanism for class IIa bacteriocins is the downregulation of the expression of the mannose phosphotransferase system (Man-PTS), which has been described for E. faecalis and L. monocytogenes.32–34 The regulatory gene rpoN also influences the mpt expression and consequently influences the development of resistance.35
Fungal lysozyme leverages the gut microbiota to curb DSS-induced colitis
Published in Gut Microbes, 2021
Ida Søgaard Larsen, Benjamin A. H. Jensen, Erica Bonazzi, Béatrice S. Y. Choi, Nanna Ny Kristensen, Esben Gjerløff Wedebye Schmidt, Annika Süenderhauf, Laurence Morin, Peter Bjarke Olsen, Lea Benedicte Skov Hansen, Torsten Schröder, Christian Sina, Benoît Chassaing, André Marette
Compared to obesity, gut health is further disrupted in IBD with clear genetic links to diminished HDP production.18,19 Bacterial translocation is well established in patients with IBD20,21 associating with reduced gut barrier function22 and a change in gut microbiota composition.23,24 Thus, obesity and IBD exhibit similar GI complications, although the links between the two phenotypes remain inadequately described.25 When the gut microbiota was evaluated by 16S rRNA gene amplicons, no similarities in microbiota composition changes within patients with obesity and IBD were reported.26 However, with more advanced network analysis, common regulation of specific enzymes involved in the phosphotransferase system or the nitrate reductase pathway has been identified between these patient groups27 supported by a change in bacterial co-abundances.28 Similarly, frameshift mutations in the pattern recognition receptor, nucleotide-binding oligomerization domain-containing protein 2 (NOD2), predispose for human IBD,29 while genetic ablation of the same protein promotes IR in HFD-fed mice.30 Patients with IBD exhibit increased prevalence of IR and nonalcoholic fatty liver disease (NAFLD), thus supporting a close connection between the mentioned diseases.31,32 Still, IR and IBD are rarely studied together, although both pathologies are increasing worldwide.33,34