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

Os lipopolissacarídeos ou LPS são essenciais para bactérias Gram-negativas, fornecendo suporte estrutural e auxiliando na evasão imunológica. O LPS consiste em lipídio A, um oligossacarídeo central e o antígeno O. A biossíntese de lipídios A começa no citoplasma com uridina difosfato N-acetilglucosamina, que sofre acilação enzimática. Forma um intermediário tetra-acilado que sofre modificações sequenciais à medida que ácidos graxos adicionais são adicionados. A acilação adicional produz um lipídio A hexa-acilado; em seguida, as glicosiltransferases ligam sequencialmente o oligossacarídeo central ao lipídio A.Este complexo lipídico A-core é então transportado através da membrana interna pelo transportador MsbA. Enquanto isso, o antígeno O é montado em um lipídio transportador no citoplasma e invertido para o periplasma. No periplasma, as unidades de antígeno O são polimerizadas e ligadas ao núcleo lipídico A, formando o LPS completo. Finalmente, o sistema de transporte de lipopolissacarídeos move o LPS através do periplasma e o incorpora à membrana externa, fortalecendo a defesa bacteriana.

formação de lipopolissacarídeos

Formation of Lipopolysaccharides

Os lipopolissacar&#237;deos (LPS) s&#227;o componentes cruciais da membrana externa de bact&#233;rias Gram-negativas, desempenhando fun&#231;&#245;es estruturais e funcionais. Eles contribuem para a estabilidade da membrana e protegem as bact&#233;rias contra respostas imunes do hospedeiro. O LPS &#233; composto por tr&#234;s regi&#245;es principais &#8212; lip&#237;deo A, um oligossacar&#237;deo central e o ant&#237;geno O. A bioss&#237;ntese e montagem do LPS envolvem um conjunto altamente coordenado de rea&#231;&#245;es enzim&#225;ticas e mecanismos de transporte. Al&#233;m disso, o LPS &#233; reconhecido como uma endotoxina, desencadeando fortes respostas imunes no hospedeiro por meio do receptor tipo Toll 4 (TLR4). Essa resposta pode levar &#224; inflama&#231;&#227;o e, em casos graves, ao choque s&#233;ptico.
Bioss&#237;ntese do Lip&#237;deo A
O lip&#237;deo A, componente t&#243;xico do LPS, &#233; sintetizado no citoplasma, a partir da uridina difosfato N-acetilglicosamina (UDP-GlcNAc). Rea&#231;&#245;es enzim&#225;ticas de acila&#231;&#227;o adicionam sequencialmente &#225;cidos graxos &#224; UDP-GlcNAc, formando um precursor de lip&#237;deo A tetra-acilado. Esse intermedi&#225;rio passa por modifica&#231;&#245;es adicionais, incluindo novas acila&#231;&#245;es, resultando no lip&#237;deo A hexa-acilado maduro. Algumas bact&#233;rias, como Salmonella e Yersinia, modificam ainda mais o lip&#237;deo A adicionando fosfoetanolamina ou aminoarabinose, aumentando a resist&#234;ncia a pept&#237;deos antimicrobianos. O lip&#237;deo A totalmente montado permanece ancorado na membrana interna, aguardando modifica&#231;&#245;es subsequentes.
Montagem do Oligossacar&#237;deo Central e do Ant&#237;geno O
O oligossacar&#237;deo central &#233; ligado sequencialmente ao lip&#237;deo A por glicosiltransferases. Essa regi&#227;o central &#233; essencial para a integridade da membrana e atua como base para a montagem do ant&#237;geno O. O ant&#237;geno O, um polissacar&#237;deo composto por unidades repetidas de a&#231;&#250;cares, &#233; sintetizado separadamente no carreador lip&#237;dico undecaprenil fosfato. O comprimento e a composi&#231;&#227;o de a&#231;&#250;cares do ant&#237;geno O variam entre as esp&#233;cies bacterianas, influenciando o reconhecimento imune e a virul&#234;ncia.
Montagem e Transporte do LPS
Ap&#243;s a liga&#231;&#227;o do lip&#237;deo A ao oligossacar&#237;deo central, a enzima flippase MsbA transloca ambas as estruturas atrav&#233;s da membrana interna. Simultaneamente, o ant&#237;geno O polimerizado &#233; translocado para o periplasma. Uma enzima ligase une covalentemente o ant&#237;geno O ao complexo lip&#237;deo A&#8211;oligossacar&#237;deo central, completando a estrutura do LPS.
O LPS maduro &#233; ent&#227;o transportado para a membrana externa pelo sistema Lpt (transporte de lipopolissacar&#237;deos), um complexo multiproteico que garante a localiza&#231;&#227;o adequada do LPS. Esse processo de transporte &#233; dependente de ATP, com o complexo LptBFG na membrana interna fornecendo a energia necess&#225;ria. A localiza&#231;&#227;o correta do LPS fortalece a membrana externa, aumentando a resist&#234;ncia bacteriana a antibi&#243;ticos, fatores imunol&#243;gicos do hospedeiro e estressores ambientais.

Formação de Lipopolissacarídeos

Os lipopolissacar&#237;deos (LPS) s&#227;o componentes cruciais da membrana externa de bact&#233;rias Gram-negativas, desempenhando fun&#231;&#245;es ...

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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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