Name: lipopolysaccharides and gram-negative defense
Uploaded: 2025-06-12T09:39:09.000Z
Duration: 1 min 19 s
Channel: JoVE

Lipopolysaccharides or LPS are essential for Gram-negative bacteria, providing structural support and aiding immune evasion.LPS consists of lipid A, a core oligosaccharide, and the O antigen.Lipid A biosynthesis begins in the cytoplasm with uridine diphosphate N-acetylglucosamine, which undergoes enzymatic acylation.It forms a tetra-acylated intermediate that undergoes sequential modifications as additional fatty acids are added.Further acylation produces a hexa-acylated lipid A; next, glycosyltransferases sequentially attach the core oligosaccharide to lipid A.This Lipid A-core complex is then transported across the inner membrane by the MsbA transporter.Meanwhile, the O antigen is assembled on a carrier lipid in the cytoplasm and flipped to the periplasm.In the periplasm, O antigen units are polymerized and ligated to the lipid A-core, forming the complete LPS.Finally, the lipopolysaccharide transport system moves the LPS across the periplasm and incorporates it into the outer membrane, strengthening bacterial defense.

vorming van lipopolysacchariden

Formation of Lipopolysaccharides

Lipopolysacchariden (LPS) zijn cruciale onderdelen van het buitenmembraan van Gram-negatieve bacteri&#235;n en vervullen zowel structurele als functionele rollen. Ze dragen bij aan de membraanstabiliteit en beschermen bacteri&#235;n tegen immuunresponsen van de gastheer. LPS bestaat uit drie hoofdregio&#8217;s: lipide A, een kernoligosaccharide en een O-antigeen. De biosynthese en samenstellen van LPS omvatten een sterk geco&#246;rdineerde reeks enzymatische reacties en transportmechanismen. Bovendien wordt LPS erkend als een endotoxine dat krachtige immuunresponsen in de gastheer activeert via Toll-like receptor 4 (TLR4). Deze respons kan leiden tot ontsteking en, in ernstige gevallen, tot septische shock.
Biosynthese van Lipide A
Lipide A, het toxische bestanddeel van LPS, wordt gesynthetiseerd in het cytoplasma, beginnend met uridinedifosfaat N-acetylglucosamine (UDP-GlcNAc). Enzymatische acyleringsreacties voegen achtereenvolgens vetzuren toe aan UDP-GlcNAc, wat leidt tot een tetra-geacyleerde lipide A-precursor. Dit tussenproduct ondergaat verdere modificaties, waaronder aanvullende acyleringen, wat leidt tot het volwassen hexa-geacyleerde lipide A. Sommige bacteri&#235;n, zoals Salmonella en Yersinia, modificeren lipide A verder door toevoeging van fosfo-ethanolamine of aminoarabinose, wat de resistentie tegen antimicrobi&#235;le peptiden verhoogt. Het volledig geassembleerde lipide A blijft verankerd in het binnenmembraan en wacht op verdere modificaties.
Assemblage van het Kernoligosaccharide en het O-antigeen
De oligosaccharide wordt opeenvolgend aan lipide A gehecht door glycosyltransferasen. Deze kernregio is essentieel voor de integriteit van het membraan en dient als structuur voor het O-antigeen. Het O-antigeen, een polysaccharide opgebouwd uit zich herhalende suikereenheden, wordt afzonderlijk gesynthetiseerd op de lipidedrager undecaprenylfosfaat. De lengte en suikercompositie van het O-antigeen vari&#235;ren tussen bacteriesoorten, wat de immuunherkenning en virulentie be&#239;nvloedt.
Samenstelling en Transport van LPS
Zodra lipide A is gekoppeld aan oligosaccharide, verplaatst het enzym MsbA-flippase beide structuren over het binnenmembraan. Tegelijkertijd wordt het gepolymeriseerde O-antigeen naar het periplasma verplaatsd. Een ligase-enzym verbindt het O-antigeen covalent aan het lipide A-kernoligosaccharidecomplex, waarmee de LPS-structuur wordt voltooid.
Het volwassen LPS wordt vervolgens naar het buitenmembraan getransporteerd door het Lpt (lipopolysaccharidetransport)-systeem, een multi-eiwitcomplex dat zorgt voor de correcte lokalisatie van LPS. Dit transportproces is ATP-afhankelijk, waarbij het LptBFG-complex in het binnenmembraan de benodigde energie levert. Een correcte plaatsing van LPS versterkt het buitenmembraan, wat de bacteri&#235;le resistentie tegen antibiotica, immuunfactoren van de gastheer en omgevingsstressoren verhoogt.

Vorming van Lipopolysacchariden

Lipopolysacchariden (LPS) zijn cruciale onderdelen van het buitenmembraan van Gram-negatieve bacteri&#235;n en vervullen zowel structurele als functionele ...

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lipopolysaccharides and gram-negative defense

Lipopolysaccharides (LPS) are important parts of the outer membrane of Gram-negative bacteria. They help stabilize the membrane and help protect bacteria from host immune responses. LPS has three main parts: lipid A, a core oligosaccharide, and an O antigen.

LPS biosynthesis and assembly depend on a coordinated set of enzymes and transport steps. The molecule is also known as an endotoxin. It can activate Toll-like receptor 4 (TLR4) in the host and trigger strong immune responses. In severe cases, this response can lead to inflammation and septic shock.

Lipid A is the toxic part of LPS. It is made in the cytoplasm, beginning with uridine diphosphate N-acetylglucosamine, or UDP-GlcNAc. Enzymes add fatty acids in a stepwise acylation process to form a tetra-acylated precursor. Further acylations produce mature hexa-acylated lipid A. Some bacteria, including Salmonella and Yersinia, add phosphoethanolamine or aminoarabinose to lipid A. These changes can increase resistance to antimicrobial peptides. The finished lipid A stays anchored in the inner membrane.

The core oligosaccharide is added next by glycosyltransferases. This core region helps maintain membrane integrity and acts as a scaffold for the O antigen. The O antigen is a repeating sugar chain made separately on the lipid carrier undecaprenyl phosphate. Its length and sugar makeup vary among bacterial species. These differences can affect immune recognition and virulence.

After lipid A is linked to the core oligosaccharide, the MsbA flippase moves both parts across the inner membrane. At the same time, the polymerized O antigen is flipped into the periplasm. A ligase then joins the O antigen to the lipid A-core complex to finish LPS assembly. The mature LPS is carried to the outer membrane by the Lpt transport system, which is a multiprotein complex. The inner-membrane LptBFG complex uses ATP for energy. Proper LPS placement strengthens the outer membrane and increases resistance to antibiotics, host immune factors, and environmental stressors.

Lipopolysaccharides and Gram-Negative Defense

lipopolysaccharides-and-gram-negative-defense

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Learn how lipopolysaccharides are built, moved, and attached in Gram-negative bacteria, and how LPS helps protect cells and trigger immune responses.

Lipopolysaccharides and Gram-Negative Defense | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

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Lipopolysaccharides and Gram-Negative Defense

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