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Bacteria
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
The cell wall has a rigid three-dimensional structure composed of cross-linked peptidogiyean, which consists of repeating units of N-acetylglucosamine and N-acetylmuramic acid. These repeating polymeric units are bound together by cross-linked pentaglycine residues. The cell envelopes of Gram-positive cells are structurally simpler than are Gram-negative cell envelopes even though they are generally thicker. In addition to an inner cytoplasmic membrane and a thick peptidoglycan layer, the Gram-positives have an outer glycocalyx or capsular layer. Gram-negative bacteria also have an inner membrane and a second membrane separated by a periplasmic space, providing a higher lipid content in Gram-negative cells (fifteen to twenty percent) compared to that (two to four percent) in Gram-positives. Figure 15.4 is an electron micrograph of a thin section of a Gram-positive bacterium, Mycobacterium flavum, and Figure 15.5 is an electron micrograph of an unidentified species of Pseudomonas, a Gram-negative bacterium.
Recombinant Antibodies
Published in Siegfried Matzku, Rolf A. Stahel, Antibodies in Diagnosis and Therapy, 2019
Melvyn Little, Sergey M. Kipriyanov
A major problem for the export of antibodies or any other proteins to the cell surface of Gram-negative bacteria such as E. coli is the double membrane. After secretion through the cytoplasmic membrane and cleavage of their signal peptide, they are then confronted by the largely impermeable outer membrane, which is characterized by an outer leaf of lipopolysaccharides. A rigid peptidoglycan network in the periplasmic space between the inner and outer membranes forms the cell wall. It is apparently anchored to the outer membrane by lipoproteins such as the major lipoprotein, Lpp, modified at its N-terminus by a lipid moiety that is integrated into the outer membrane. A large number of trimeric protein complexes formed by a channel-forming class of proteins known as the porins are also integrated into the outer membrane, where they permit the diffusion of molecules up to a molecular weight of about 500 Da. The porins and several other outer membrane proteins, including the abundant outer membrane protein A (OmpA), appear to contain several membrane-spanning β-sheets joined by surface loops.
Brucella: A Foodborne Pathogen
Published in Dongyou Liu, Handbook of Foodborne Diseases, 2018
Brucella are nonmotile and do not have spores. The cell wall of Brucella is typical for gram-negative bacteria. The outer membrane, approximately 4–5 nm in thickness, is composed of asymmetric layers of LPS and phospholipids and is supported by an underlying 3–5 nm layer of peptidoglycan. Some proteins, such as OmpA, are covalently bound to the peptidoglycan layer and stabilize the outer membrane. The hydrophobic region of the membrane provides an anchor for proteins and forms a functional and structural barrier between the periplasm and the exterior of the cell. The periplasmic space varies from 3 to 30 nm. Porins in the outer membrane function as channels to the interior of the cell. Other proteins, such as lipoproteins, are also embedded in the outer membrane.
New perspectives in the antibiotic treatment of mechanically ventilated patients with infections from Gram-negatives
Published in Expert Review of Anti-infective Therapy, 2021
Marios Karvouniaris, Konstantinos Pontikis, Thomas Nitsotolis, Garyphallia Poulakou
Though chemically related to ceftazidime and cefepime, this novel cefalosporin possesses unique properties that enable the molecule to remain stable in the presence of all classes of β-lactamases, Ambler classes A, C, D, and B class metallo-β-lactamases as well. The side chain at position 3 of the drug contains a catechol moiety, forms complexes with ferric iron, and the drug is transported as a siderophore (‘Trojan horse strategy’). This process facilitates high concentrations of the antibiotic in the periplasmic space to inhibit the synthesis of peptidoglycans. The spectrum of activity is broad, and the corresponding MIC90 values in 2016 for A. baumannii, K. pneumoniae, P. aeruginosa, and Stenotrophomonas maltophilia were 4, 1, 0.5, and 0.25 mg/L, respectively (all within the range of susceptibility) [102]. More in vitro data from Canadian ICUs, during 2015–17, confirmed universal susceptibility of Enterobacterales, MDR P. aeruginosa, and A. baumannii to cefiderocol [103].
An overview on the recently discovered iota-carbonic anhydrases
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2021
Alessio Nocentini, Claudiu T. Supuran, Clemente Capasso
In bacteria, the CA catalysed reaction is the only known pathway to obtain and balance endogenous levels of CO2, H2CO3 (carbonic acid), HCO3-, and CO32-(carbonate) rapidly7,24–26. In bacteria, CO2 enters and leaves the bacterial cell by passive diffusion, while bicarbonate is imported directly into the cell through bicarbonate transporters27. Gram-negative bacteria have a periplasmic CA in their periplasmic space, for avoiding the loss of CO2 through diffusion. This enzyme converts faster the CO2 generated from the bacterial metabolism and that coming from the atmosphere into bicarbonate. HCO3- is thereafter pumped into the cytoplasm by bicarbonate transporters and, there, converted into CO2 by cytoplasmic forms of CAs belonging to the β- and/or γ-CA classes15,24,27. Thus, the bicarbonate transporters and bacterial CA enzymes provide CO2 and HCO3- to sustain bacterial metabolism15,24,27. The natural reaction of interconversion of CO2 and H2O into HCO3- and H+ cannot quickly supply CO2 and HCO3- to the bacterial metabolism, as already mentioned, since the reaction rate is too low at physiological pH.
Functional analysis and cryo-electron microscopy of Campylobacter jejuni serine protease HtrA
Published in Gut Microbes, 2020
Urszula Zarzecka, Alessandro Grinzato, Eaazhisai Kandiah, Dominik Cysewski, Paola Berto, Joanna Skorko-Glonek, Giuseppe Zanotti, Steffen Backert
Bacterial HtrA proteases constitute periplasmic enzymes involved in protein quality control, which is especially important under environmental stress conditions. When certain periplasmic proteins lose their conformation and functionality due to stressors, then HtrA acts as a protease and/or as a chaperone.45 In both cases, the level of toxic proteins is reduced. Another aspect of HtrA’s functioning is its role in the non-periplasmic space. In many pathogenic bacteria, including H. pylori and C. jejuni, the HtrAs can also target host cell factors.21 Such important functions, especially the proteolytic activity, must be strictly controlled, and in this case the quaternary organization can be involved. For this purpose, we focused our current research on: (i) proving that the HtrACj is able to digest unstructured β-casein and reduced lysozyme, while properly folded lysozyme remains undigested (Figure 1); (ii) determining that the HtrACj protein has high thermal stability which is in agreement with the ability of the protein to function under stress conditions35 (Table 1); (iii) demonstrating the preferred cleavage sites of this protease (Figure 2); (iv) establishing a 3D model of the dodecameric, structurally active form of HtrACj by Cryo-EM (Figure 3–5); and (v) performing analysis of the size of oligomeric forms for the proteolytically active HtrACj that allowed us to discover the basic, stable resting form for this protease-hexamer (Figure 6).