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

Lipopolisacharydy lub LPS są niezbędne dla bakterii Gram-ujemnych, zapewniając wsparcie strukturalne i pomagając w unikaniu odporności. LPS składa się z lipidu A, oligosacharydu rdzeniowego i antygenu O. Biosynteza lipidów A rozpoczyna się w cytoplazmie z difosforanem urydyny N-acetyloglukozaminą, która ulega acylacji enzymatycznej. Tworzy tetra-acylowany półprodukt, który ulega sekwencyjnym modyfikacjom w miarę dodawania dodatkowych kwasów tłuszczowych. Dalsza acylacja wytwarza heksa-acylowany lipid A; następnie glikozylotransferazy sekwencyjnie przyłączają oligosacharyd rdzeniowy do lipidu A.Ten kompleks rdzenia lipidowego A jest następnie transportowany przez błonę wewnętrzną przez transporter MsbA. Tymczasem antygen O jest gromadzony na lipidie nośnikowym w cytoplazmie i przenoszony do peryplazmy. W peryplazmie jednostki antygenu O są polimeryzowane i ligowane do lipidowego rdzenia A, tworząc kompletny LPS. Wreszcie, system transportu lipopolisacharydów przesuwa LPS przez peryplazmę i włącza go do błony zewnętrznej, wzmacniając obronę bakteryjną.

biosynteza lipopolisacharydów

Formation of Lipopolysaccharides

Lipopolisacharydy (LPS) s&#261; kluczowymi sk&#322;adnikami zewn&#281;trznej b&#322;ony bakterii Gram-ujemnych, pe&#322;ni&#261;c funkcje strukturalne i funkcjonalne. Zapewniaj&#261; stabilno&#347;&#263; b&#322;ony i chroni&#261; bakterie przed odpowiedzi&#261; immunologiczn&#261; gospodarza. LPS sk&#322;ada si&#281; z trzech g&#322;&#243;wnych region&#243;w: lipidu A, rdzeniowego oligosacharydu oraz antygenu O. Biosynteza i monta&#380; LPS obejmuj&#261; &#347;ci&#347;le skoordynowany zestaw reakcji enzymatycznych i mechanizm&#243;w transportowych. LPS pe&#322;ni r&#243;wnie&#380; funkcj&#281; endotoksyny, aktywuj&#261;c siln&#261; odpowied&#378; immunologiczn&#261; gospodarza za po&#347;rednictwem receptora toll-podobnego 4 (TLR4). Taka odpowied&#378; mo&#380;e prowadzi&#263; do stanu zapalnego, a w ci&#281;&#380;kich przypadkach do wstrz&#261;su septycznego.
Biosynteza lipidu A
Lipid A, b&#281;d&#261;cy toksycznym sk&#322;adnikiem LPS, jest syntetyzowany w cytoplazmie z urydynodifosforanu N-acetyloglukozaminy (UDP-GlcNAc). Reakcje acylacji enzymatycznej stopniowo przy&#322;&#261;czaj&#261; kwasy t&#322;uszczowe do UDP-GlcNAc, tworz&#261;c prekursora lipidu A o czterech resztach acylowych. Intermediat ten podlega dalszym modyfikacjom, w tym kolejnym acylacjom, prowadz&#261;c do powstania dojrza&#322;ego lipidu A z sze&#347;cioma resztami acylowymi. Niekt&#243;re bakterie, takie jak Salmonella i Yersinia, dodatkowo modyfikuj&#261; lipid A poprzez do&#322;&#261;czanie fosfoetanoloaminy lub aminocukru arabinozy, zwi&#281;kszaj&#261;c odporno&#347;&#263; na peptydy przeciwdrobnoustrojowe. W pe&#322;ni zmontowany lipid A pozostaje zakotwiczony w wewn&#281;trznej b&#322;onie i oczekuje na dalsze modyfikacje.
Monta&#380; rdzeniowego oligosacharydu i antygenu O
Rdzeniowy oligosacharyd jest kolejno do&#322;&#261;czany do lipidu A przez glikozylotransferazy. Region ten jest niezb&#281;dny do utrzymania integralno&#347;ci b&#322;ony i stanowi rusztowanie dla antygenu O. Antygen O to polisacharyd z&#322;o&#380;ony z powtarzaj&#261;cych si&#281; jednostek cukrowych, syntetyzowany oddzielnie na no&#347;niku lipidowym &#8211; fosforanie undekaprenylu. D&#322;ugo&#347;&#263; i sk&#322;ad cukrowy antygenu O r&#243;&#380;ni&#261; si&#281; mi&#281;dzy gatunkami bakterii, wp&#322;ywaj&#261;c na rozpoznawalno&#347;&#263; immunologiczn&#261; i zjadliwo&#347;&#263;.
Monta&#380; i transport LPS
Po po&#322;&#261;czeniu lipidu A z rdzeniowym oligosacharydem enzym MsbA (flippaza) przenosi oba elementy przez wewn&#281;trzn&#261; b&#322;on&#281;. Jednocze&#347;nie spolimeryzowany antygen O jest transportowany do przestrzeni peryplazmatycznej. Enzym ligaza &#322;&#261;czy kowalencyjnie antygen O z kompleksem lipid A&#8211;oligosacharyd rdzeniowy, ko&#324;cz&#261;c struktur&#281; LPS.
Dojrza&#322;y LPS jest nast&#281;pnie transportowany do zewn&#281;trznej b&#322;ony przez system Lpt (transport lipopolisacharydu), b&#281;d&#261;cy kompleksem multiproteinowym zapewniaj&#261;cym prawid&#322;ow&#261; lokalizacj&#281; LPS. Proces ten jest zale&#380;ny od ATP &#8211; energi&#281; zapewnia kompleks LptBFG w wewn&#281;trznej b&#322;onie. Prawid&#322;owa lokalizacja LPS wzmacnia zewn&#281;trzn&#261; b&#322;on&#281;, zwi&#281;kszaj&#261;c odporno&#347;&#263; bakterii na antybiotyki, czynniki immunologiczne gospodarza oraz stres &#347;rodowiskowy.

Biosynteza lipopolisacharydów

Lipopolisacharydy (LPS) s&#261; kluczowymi sk&#322;adnikami zewn&#281;trznej b&#322;ony bakterii Gram-ujemnych, pe&#322;ni&#261;c funkcje strukturalne i ...

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Microbial Metabolism

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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.

microbiology

Lipopolysaccharides and Gram-Negative Defense

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