Lipopolysaccharide Is An Important Cell Wall Component Of

Lipopolysaccharide (LPS) is the significant component of the outer membrane of Gram-negative bacteria. Lipopolysaccharide is localized in the external layer of the membrane and also is, in noncapsulated strains, exposed on the cell surchallenge.

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Structure

Intact bacterial lipopolysaccharides are macromolecules of molecular mass 10‑20 kDa made up of three structural components (Figure 1):

A hydrophobic lipid section, lipid A, which is responsible for the toxic properties of the molecule,A hydrophilic core polysaccharide chain, andA repeating hydrophilic O-antigenic oligosaccharide side chain that is particular to the bacterial seroform.1
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Figure 1.

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General framework for bacterial lipopolysaccharides. See the text for comprehensive explanation concerning each section. Abbreviations: KDO: 3‑deoxy-α-D-mannooctulosonic acid; Hep: Heptushed (ketoheptose); NGa: Galactosamine; NGc: Glucosamine.


The lipid A core is made up of a β-glucosamine-(1→6)-glucosamine-1-phosphate base via fatty acid esters attached to both carbohydrates. The acyl chain size and also variety of acyl teams may differ between bacterial species however are relatively conserved within a species. The inner polysaccharide core commonly has between 1 and also 4 molecules of the KDO (3‑deoxy-α-D-manno-octulosonic acid) attached to the disaccharide core. KDO is especially associated with lipopolysaccharide, and also biologically active lipid A was thmust require at least one KDO residue for bacterial survival.2 However, an Escherichia coli K-12 suppressor strain that is KDO deficient demonstrates that the KDO necessity is not absolute for vicapability.3The KDO-containing inner core likewise is modified with heptulose (ketoheptose) monosaccharides, the a lot of widespread of which is L-glycero-α-D-manno-heptopyranose. The inner core glyhave the right to residues are typically phosphorylated or modified with phosphate-containing teams, e.g., pyrophosphate or 2‑aminoethylphosphate. The phosphate teams of lipopolysaccharides increase the all at once negative charge of the cell membrane and also assist to stabilize the framework.The external core of the lipopolysaccharide includes more widespread hexoses, consisting of glucose, galactose, and N-acetylglucosamine and is structurally more diverse than the inner core.The O-antigen is a repeating oligosaccharide unit generally comprised of two to 6 sugars. The O-antigen is the main structural constituent of lipopolysaccharide that differentiates bacteria. The distinctive O-antigen structures have been supplied to recognize and also assign serogroups to Escherichia coli, Salmonella enterica, and also Vibrio cholerae.4 Lipopolysaccharides from rough mutant strains of E. coli lack the O-antigen percentage of the structure.The core section and also the lipid A section of a lipopolysaccharide may have some variability in framework, while the O-antigen has actually a high degree of structural variability as well as varicapacity in the number of repeating devices. These distinctions lead to a far-reaching amount of heterogeneity in LPS preparations. Because LPS is heterogeneous and tends to develop aggreentrances of varying sizes, tright here is a reported "molecular mass" range for these aggregateways of 1‑4 million Dalton or greater. When the LPS is treated via sodium dodecyl sulfate (SDS) and also warm, the molecular mass is ~50‑100 kDa.5

Functions and also Applications

Within Gram-negative bacteria, the membrane lipopolysaccharides safeguard the bacterium versus the action of bile salts and lipophilic antibiotics.6

Lipopolysaccharides are heat-steady endotoxins and have lengthy been recognized as a vital variable in septic shock (septicemia) in humans1,7 and also, more generally, in inducing a strong immune response in normal mammalian cells. The lipid A moiety has been figured out as instrumental to the endotoxin activity of lipopolysaccharide. This was demonstrated, Galanos, et al., by finding the same bioactive results, including endotoxic task, between fabricated and also natural-sourced E. coli lipid A preparations.8 The active receptor for lipopolysaccharide has actually been established as the CD14/TLR4/MD2 receptor complex, which promotes the secretion of proinflammatory cytokines including tumor necrosis factor-α and also interleukin-1.9 While the lipid A component is primarily responsible for immune response activation, the polysaccharide component of Salmonella enterica LPS is also vital for NF-κB activation.10

Lipopolysaccharide preparations have been used in research study for the elucidation of LPS framework,11 metabolism,12 immunology,13 physiology,14 toxicity,15 and also biosynthesis.16 They have actually likewise been used to induce synthesis and secretion of growth-cultivating components such as interleukins.17,18 Due to the fact that of its connection to septicemia, lipopolysaccharide has been stupassed away to recognize feasible targets for antibodies and also inhibitors to LPS biosynthesis.19,20

Extraction and Purification

Lipopolysaccharides deserve to be all set by extractivity from TCA,21 phenol,22,23 or phenol-chloroform-petroleum ether (for stormy strains).24 TCA extracted lipopolysaccharides are structurally comparable to the phenol extracted ones, with similar electrophoretic patterns and endotoxicity. The main distinctions are in the amounts of nucleic acid and also protein contaminants remaining after extraction. The TCA extracts contain ~2% RNA and ~10% denatured proteins, while phenol extracts contain approximately 60% RNA and 1.