Chitosan as a wound dressing starting material: antimicrobial Properties and mode of action

Fighting bacterial resistance is one of the concerns in modern days, as antibiotics remain the main resource of bacterial control. Data shows that for every antibiotic developed, there is a microorganism that becomes resistant to it. Natural polymers, as the source of antibacterial agents, offer a new way to fight bacterial infection. The advantage over conventional synthetic antibiotics is that natural antimicrobial agents are biocompatible, non-toxic, and inexpensive. Chitosan is one of the natural polymers that represent a very promising source for the development of antimicrobial agents. In addition, chitosan is biodegradable, non-toxic, and most importantly, promotes wound healing, features that makes it suitable as a starting material for wound dressings. This paper reviews the antimicrobial properties of chitosan and describes the mechanisms of action toward microbial cells as well as the interactions with mammalian cells in terms of wound healing process. Finally, the applications of chitosan as a wound-dressing material are discussed along with the current status of chitosan-based wound dressings existing on the market.publishedVersio

Molecular insight into a new low affinity xylan binding module from the xylanolytic gut symbiont Roseburia intestinalis

Efficient capture of glycans, the prime metabolic resources in the human gut, confers a key competitive advantage for gut microbiota members equipped with extracellular glycoside hydrolases (GHs) to target these substrates. The association of glycans to the bacterial cell surface is typically mediated by carbohydrate binding modules (CBMs). Here, we report the structure of RiCBM86 appended to a GH family 10 xylanase from Roseburia intestinalis. This CBM represents a new family of xylan binding CBMs present in xylanases from abundant and prevalent healthy human gut Clostridiales. RiCBM86 adopts a canonical β-sandwich fold, but shows structural divergence from known CBMs. The structure of RiCBM86 has been determined with a bound xylohexaose, which revealed an open and shallow binding site. RiCBM86 recognizes only a single xylosyl ring with direct hydrogen bonds. This mode of recognition is unprecedented amongst previously reported xylan binding type-B CBMs that display more extensive hydrogen-bonding patterns to their ligands or employ Ca2+ to mediate ligand-binding. The architecture of RiCBM86 is consistent with an atypically low binding affinity (KD about 0.5 mm for xylohexaose) compared to most xylan binding CBMs. Analyses using NMR spectroscopy corroborated the observations from the complex structure and the preference of RiCBM86 to arabinoxylan over glucuronoxylan, consistent with the largely negatively charged surface flanking the binding site. Mutational analysis and affinity electrophoresis established the importance of key binding residues, which are conserved in the family. This study provides novel insight into the structural features that shape low-affinity CBMs that mediate extended bacterial glycan capture in the human gut niche. Databases: Structural data are available in the protein data bank database under the accession number 6SGF. Sequence data are available in the GenBank database under the accession number EEV01588.1. The assignment of the Roseburia intestinalis xylan binding module into the CBM86 new family is available in the CAZy database (http://www.cazy.org/CBM86.html)

The effect of linker conformation on performance and stability of a two-domain lytic polysaccharide monooxygenase

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Genome Mining of Streptomyces sp. YIM 130001 Isolated From Lichen Affords New Thiopeptide Antibiotic

Schneider O, Simic N, Aachmann FL, et al. Genome Mining of Streptomyces sp. YIM 130001 Isolated From Lichen Affords New Thiopeptide Antibiotic. FRONTIERS IN MICROBIOLOGY. 2018;9: 3139.Streptomyces bacteria are recognized as an important source for antibiotics with broad applications in human medicine and animal health. Here, we report the isolation of a new lichen-associating Streptomyces sp. YIM 130001 from the tropical rainforest in Xishuangbanna (Yunnan, China), which displayed antibacterial activity against Bacillus subtilis. The draft genome sequence of this isolate strain revealed 18 putative biosynthetic gene clusters (BGCs) for secondary metabolites, which is an unusually low number compared to a typical streptomycete. Inactivation of a (antibiotic dehydrogenase-encoding gene from the BGC presumed to govern biosynthesis of a thiopeptide resulted in the loss of bioactivity. Using comparative HPLC analysis, two peaks in the chromatogram were identified in the extract from the wild-type strain, which were missing in the extract from the mutant. The compounds corresponding to the identified peaks were purified, and structure of one compound was elucidated using NMR. The compound, designated geninthiocin B, showed high similarity to several 35-membered macrocyclic thiopeptides geninthiocin, Val-geninthiocin and berninamycin A. Bioinformatics analysis of the geninthiocin B BGC revealed its close homology to that of berninamycins

Differential bacterial capture and transport preferences facilitate co-growth on dietary xylan in the human gut

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NMR and fluorescence spectroscopies reveal the preorganized binding site in family 14 carbohydrate-binding module from human chitotriosidase

Carbohydrate-binding modules (CBM) play important roles in targeting and increasing the concentration of carbohydrate active enzymes on their substrates. Using NMR to get the solution structure of CBM14, we can gain insight into secondary structure elements and intramolecular interactions with our assigned nuclear overhauser effect peaks. This reveals that two conserved aromatic residues (Phe437 and Phe456) make up the hydrophobic core of the CBM. These residues are also responsible for connecting the two β-sheets together, by being part of β2 and β4, respectively, and together with disulfide bridges, they create CBM14’s characteristic “hevein-like” fold. Most CBMs rely on aromatic residues for substrate binding; however, CBM14 contains just a single tryptophan (Trp465) that together with Asn466 enables substrate binding. Interestingly, an alanine mutation of a single residue (Leu454) located behind Trp465 renders the CBM incapable of binding. Fluorescence spectroscopy performed on this mutant reveals a significant blue shift, as well as a minor blue shift for its neighbor Val455. The reduction in steric hindrance causes the tryptophan to be buried into the hydrophobic core of the structure and therefore suggests a preorganized binding site for this CBM. Our results show that both Trp465 and Asn466 are affected when CBM14 interacts with both (GlcNAc)3 and β-chitin, that the binding interactions are weak, and that CBM14 displays a slightly higher affinity toward β-chitin.publishedVersio

Resonance assignments for the apo-form of the cellulose-active lytic polysaccharide monooxygenase TaLPMO9A

The apo-form of the 24.4 kDa AA9 family lytic polysaccharide monooxygenase TaLPMO9A from Thermoascus aurantiacus has been isotopically labeled and recombinantly expressed in Pichia pastoris. In this paper, we report the 1H, 13C, and 15N chemical shift assignments, as well as an analysis of the secondary structure of the protein based on the secondary chemical shifts.Resonance assignments for the apo-form of the cellulose-active lytic polysaccharide monooxygenase TaLPMO9ApublishedVersio

NMR structure of a lytic polysaccharide monooxygenase provides insight into copper binding, protein dynamics, and substrate interactions

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