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

Lipopolysaccharide oder LPS sind für gramnegative Bakterien unerlässlich, da sie strukturelle Unterstützung bieten und die Immunevasion unterstützen. LPS besteht aus dem Lipid A, einem Kern-Oligosaccharid, und dem O-Antigen. Die Lipid-A-Biosynthese beginnt im Zytoplasma mit dem Uridindiphosphat N-Acetylglucosamin, das eine enzymatische Acylierung durchläuft. Es bildet ein tetra-acyliertes Zwischenprodukt, das sequentielle Modifikationen erfährt, wenn zusätzliche Fettsäuren hinzugefügt werden. Durch die weitere Acylierung entsteht ein hexa-acyliertes Lipid A; Als nächstes binden Glykosyltransferasen nacheinander das Kernoligosaccharid an Lipid A.Dieser Lipid-A-Kern-Komplex wird dann durch den MsbA-Transporter durch die innere Membran transportiert. In der Zwischenzeit wird das O-Antigen auf einem Trägerlipid im Zytoplasma montiert und in das Periplasma umgedreht. Im Periplasma werden O-Antigeneinheiten polymerisiert und an den Lipid-A-Kern ligiert, wodurch das vollständige LPS gebildet wird. Schließlich bewegt das Lipopolysaccharid-Transportsystem das LPS durch das Periplasma und baut es in die äußere Membran ein, wodurch die bakterielle Abwehr gestärkt wird.

bildung von lipopolysacchariden

Formation of Lipopolysaccharides

Lipopolysaccharide (LPS) sind entscheidende Bestandteile der &#228;u&#223;eren Membran gramnegativer Bakterien und &#252;bernehmen sowohl strukturelle als auch funktionelle Aufgaben. Sie tragen zur Stabilit&#228;t der Membran bei und sch&#252;tzen die Bakterien vor Immunantworten des Wirts. LPS bestehen aus drei Hauptkomponenten &#8211; Lipid A, einem Core-Polysaccharid und einem O-Antigen. Die Biosynthese und Assemblierung von LPS erfolgt durch eine hoch koordinierte Abfolge enzymatischer Reaktionen und Transportmechanismen. Zudem wird LPS als Endotoxin erkannt, das durch den Toll-like-Rezeptor 4 (TLR4) starke Immunreaktionen im Wirt ausl&#246;st. Diese Reaktion kann zu Entz&#252;ndungen und in schweren F&#228;llen zu einem septischen Schock f&#252;hren.
Biosynthese von Lipid A
Lipid A, die toxische Komponente des LPS, wird im Zytoplasma synthetisiert, beginnend mit Uridindiphosphat-N-acetylglucosamin (UDP-GlcNAc). Enzymatische Acylierungsreaktionen f&#252;gen nacheinander Fetts&#228;uren an UDP-GlcNAc an, wodurch ein vierfach acylierter Vorl&#228;ufer des Lipid A entsteht. Dieses Zwischenprodukt wird weiter modifiziert, unter anderem durch zus&#228;tzliche Acylierungen, was zum finalen, sechsfach acylierten Lipid A f&#252;hrt. Einige Bakterien, wie Salmonella und Yersinia, modifizieren Lipid A zus&#228;tzlich durch die Anlagerung von Phosphoethanolamin oder Aminoarabinose, was die Resistenz gegen antimikrobielle Peptide erh&#246;ht. Das vollst&#228;ndig zusammengesetzte Lipid A bleibt in der inneren Membran verankert und wartet auf weitere Modifikationen.
Assemblierung von Core-Polysaccharid und O-Antigen
Das Core-Polysaccharid (oder Kernregion) wird durch Glycosyltransferasen schrittweise an Lipid A angeheftet. Die Kernregion ist wesentlich f&#252;r die Integrit&#228;t der Membran und dient als Ger&#252;st f&#252;r das O-Antigen. Das O-Antigen, ein Polysaccharid aus sich wiederholenden Zuckerbausteinen, wird separat auf dem Lipidtr&#228;ger Undecaprenylphosphat synthetisiert. L&#228;nge und Zuckerzusammensetzung des O-Antigens variieren zwischen den Bakterienarten und beeinflussen die Immunerkennung sowie die Virulenz.
Aufbau und Transport von LPS
Sobald Lipid A mit dem Core-Polysaccharid verbunden ist, transloziert das Enzym MsbA-Flippase beide Strukturen durch die innere Membran. Gleichzeitig wird das polymerisierte O-Antigen in den Periplasma-Raum &#252;berf&#252;hrt. Eine Ligase verbindet das O-Antigen kovalent mit dem Lipid-A-Kern-Komplex und vervollst&#228;ndigt somit die Struktur des LPS.
Das fertige LPS wird anschlie&#223;end durch das Lpt-System (Lipopolysaccharid-Transportsystem), ein Multiproteinkomplex, der die korrekte Lokalisierung des LPS gew&#228;hrleistet, zur &#228;u&#223;eren Membran transportiert. Dieser Transportvorgang ist ATP-abh&#228;ngig, wobei der LptBFG-Komplex in der inneren Membran die notwendige Energie bereitstellt. Die korrekte Lokalisierung von LPS verst&#228;rkt die &#228;u&#223;ere Membran und erh&#246;ht die Resistenz der Bakterien gegen&#252;ber Antibiotika, immunologischen Abwehrmechanismen des Wirts sowie Umwelteinfl&#252;ssen.

Bildung von Lipopolysacchariden

Lipopolysaccharide (LPS) sind entscheidende Bestandteile der &#228;u&#223;eren Membran gramnegativer Bakterien und &#252;bernehmen sowohl strukturelle als ...

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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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key terms and concepts

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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