Recombinant Antibodies
Siegfried Matzku, Rolf A. Stahel in Antibodies in Diagnosis and Therapy, 2019
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
Dongyou Liu in 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.
Introduction to Clinical Microbiology
Keith Struthers in Clinical Microbiology, 2017
The cell wall of gram-negative bacteria is more complex than that of gram-positive bacteria (Figure 1.6). The outer lipid bilayer has proteins, such as adhesins, and flagella traversing it. Porins act as channels that allow hydrated molecules to pass through the membrane. From the periplasmic space, molecules can be transported across the cytoplasmic membrane into the cell. It should be noted that porins enable antibiotics such as the β-lactams to reach their site of action. Benzylpenicillin is not effective against most gram-negative organisms because it is not sufficiently polar to pass through a porin channel. Ampicillin, a derivative of benzylpenicillin, differs in the addition of an amino group on the side chain (Figure 1.10). The polar ampicillin passes through the hydrated porin channel into the periplasmic space where it can act on the PBP.
Strengths and caveats of identifying resistance genes from whole genome sequencing data
Published in Expert Review of Anti-infective Therapy, 2022
Brian M. Forde, David M. P. De Oliveira, Caitlin Falconer, Bianca Graves, Patrick N. A. Harris
Drug efflux systems are a major mediator of AMR. These systems encoded by genes either on the chromosome or within mobile genetic elements (MGEs) mediate the active removal of antimicrobial agents from the cytoplasmic and periplasmic space [14]. To date, six drug efflux systems have been characterized. These include resistance-nodulation-division (RND), major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), small multidrug resistance (SMR), ATP-binding cassette (ABC), and proteobacterial antimicrobial compound efflux (PACE) families [15,16]. In conjunction with these systems, mutations in outer membrane protein channels (porins) further act to reduce antibiotic penetration and accumulation in bacterial cells. Mutations leading to the downregulation, or complete loss of porins are known to result in the decreased penetration of hydrophilic agents such as β-lactams (including carbapenems) and fluoroquinolones [17,18].
Multidrug-resistant Klebsiella pneumoniae: mechanisms of resistance including updated data for novel β-lactam-β-lactamase inhibitor combinations
Published in Expert Review of Anti-infective Therapy, 2021
Irene Galani, Ilias Karaiskos, Helen Giamarellou
Porins are transmembrane β-barrel proteins that exist as trimers, creating channels of defined size and are found in the outer membrane of Gram-negative bacteria. Porins regulate the nonspecific diffusion of hydrophilic solutes and other small molecules through the outer membrane. Enterobacterales commonly express two major nonspecific porins with similar functions, differing in their permeability to small molecules. These nonspecific porins play an important role in nutrient acquisition but also mediate the passive diffusion of antibiotics across the outer membrane and are closely associated with antibiotic resistance in the Gram-negative bacteria [75,76]. Decreased outer membrane porin expression in antibiotic resistant isolates has been correlated with an increased minimum inhibitory concentration (MIC) to multiple antibiotics, most commonly those that target peptidoglycan synthesis [77–79].
Chlamydia trachomatis vaccines for genital infections: where are we and how far is there to go?
Published in Expert Review of Vaccines, 2021
Luis M. de la Maza, Toni L Darville, Sukumar Pal
MOMP is highly antigenic, contains B- and T-cell epitopes and accounts for ~60% of the outer membrane protein mass [34,87]. MOMP belongs to a group of proteins called porins important for the passive transport of ions, sugars and nucleotides across the outer membrane of Gram-negative bacteria [88,89]. Porins have a structural topology comprised of antiparallel β-strands spanning the outer membrane, a water-filled inner channel, tight β-turns extending into the periplasmic region and flexible loops reaching beyond the extracellular surface. Because of their DNA sequence heterogeneity, that is used to classify C. trachomatis into different serovars, the extracellular loops of MOMP are called variable domains (VD) [85,90]. The VD are the main target of the antibody responses while the T-cell epitopes are mostly located in the β-strands [91–93]. MOMP has a monomeric molecular weight of 39.5 kDa, a hydrophobic residue content of ~40% and migration patterns on SDS-PAGE gels consistent with trimeric oligomerization [94].
Related Knowledge Centers
- Bacterial Outer Membrane
- Beta Barrel
- Diffusion
- Molecule
- Protein
- Cell Membrane
- Membrane Transport Protein
- Passive Transport
- Ion Channel
- Gram-Negative Bacteria