Name: how proteins shape cell membranes
Uploaded: 2023-04-30T09:16:36.000Z
Duration: 1 min 15 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

9-12.B.1.4.a

Mechanisms of Membrane-bending

Uma membrana tem uma curvatura positiva quando se dobra para o lado interno ou citoplasmático. Em contraste, uma membrana tem uma curvatura negativa se se curvar para o lado externo ou extracelular.
Existem vários mecanismos que podem causar flexão da membrana.
A flexão da membrana induzida por lipídios é devida à agregação assimétrica de lipídios específicos na membrana.
Os lipídios com grandes grupos de cabeça induzem uma curvatura positiva da membrana, enquanto os lipídios com pequenos grupos de cabeça produzem uma curvatura negativa da membrana.
O andaime de proteínas é outro mecanismo em que as proteínas deformam a membrana ou estabilizam uma membrana já deformada.
Em um mecanismo diferente, os domínios de proteínas hidrofóbicas são inseridos reversivelmente em uma camada da membrana para aumentar sua área em comparação com a outra camada. Essa assimetria força a membrana a dobrar.
Finalmente, as forças de empurrar e puxar geradas pela montagem e desmontagem do citoesqueleto e suas proteínas motoras associadas também podem dobrar a membrana para formar projeções, como filopódios em células epiteliais.

mecanismos de flexão da membrana

As membranas vivas são flexíveis devido à sua natureza de mosaico fluido; no entanto, a sua curvatura em diferentes formas é um processo ativo regulado por lipídios e proteínas específicos. A flexão da membrana pode ser transitória, como observada nas vesículas, ou estável por um longo período, como nas microvilosidades. As células regulam o tamanho, a localização e a duração da curvatura da membrana. A flexão da membrana pode ocorrer devido a alterações intrínsecas na composição lipídica ou pela associação extrínseca com diferentes proteínas. As proteínas envolvidas na criação de assimetria na membrana, ou pelo agrupamento de lipídios específicos, desempenham um papel essencial na flexão da membrana induzida por lipídios. A forma das proteínas integrais também pode afetar a flexão da membrana. Por exemplo, proteínas transmembranares de formato cônico, ou cônico inverso, produzem flexão na membrana. A inserção de proteínas anfipáticas, como a epsina, em uma das camadas também resulta na flexão da membrana. As proteínas curvas, como as proteínas Bin/anfifisina/Rvs, ou dímero BAR, criam uma curvatura positiva da membrana, enquanto a proteína BAR inversa, ou I-BAR, induz uma curvatura negativa na membrana. As proteínas BAR também inserem o seu domínio hidrofóbico na membrana, o que aumenta ainda mais a curvatura da membrana. Além dos mecanismos bem estabelecidos, o aglomeramento de proteínas é um mecanismo recentemente descoberto para a flexão da membrana, onde a pressão lateral gerada pelas interações proteína-proteína impulsiona a flexão da membrana. Os citoesqueletos também desempenham um papel significativo na flexão da membrana, e as forças geradas por eles são responsáveis pela morfologia de algumas organelas, como o retículo endoplasmático e o aparelho de Golgi. As organelas celulares, como o retículo endoplasmático, o aparelho de Golgi e as mitocôndrias, possuem membranas intrincadamente dobradas. Essas dobras são essenciais para o seu funcionamento. A flexão da membrana também é necessária para a cisão da membrana, fusão da membrana e ativação da enzima sensível à curvatura da membrana. Mutações em genes que produzem proteínas de flexão da membrana, como miotubularina, anfifisina-2 e dinamina-2, podem levar a um grupo de distúrbios neuromusculares conhecidos como miopatias centronucleares.

Mecanismos de flexão da membrana

As membranas vivas são flexíveis devido à sua natureza de mosaico fluido; No entanto, sua dobra em diferentes formas é um processo ativo regulado por ...

Education

JoVE Core

Cell Biology

Biologia Celular

Unit 1

Unidade 1

Membrane Structure and Components

Estrutura e Componentes da Membrana

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

how proteins shape cell membranes

Cell membranes can bend into many shapes because they are flexible and made of a fluid mosaic. That bending can be temporary, as in vesicles, or long-lasting, as in microvilli. Cells control the size, place, and time of membrane curvature.

Membrane bending can start inside the membrane itself or from proteins attaching to it. Changes in lipid makeup can create curvature, and proteins can help by making the membrane asymmetric or by clustering certain lipids. The shape of integral proteins also matters. Conical or inverse-conical transmembrane proteins can push the membrane to bend.

Some proteins bend membranes by inserting part of themselves into one layer of the membrane. Amphipathic proteins, such as epsin, do this and promote curvature. BAR proteins, short for Bin/amphiphysin/Rvs proteins, create positive curvature, while I-BAR proteins create negative curvature. BAR proteins can also add to bending by placing a hydrophobic domain into the membrane.

Protein crowding is another way membranes bend. In this case, proteins packed close together create lateral pressure, and that pressure drives curvature. The cytoskeleton also helps shape membranes. Its forces are important for the form of organelles such as the endoplasmic reticulum and Golgi apparatus.

The folded membranes of the endoplasmic reticulum, Golgi apparatus, and mitochondria are important for their function. Membrane bending also supports membrane scission, membrane fusion, and the activation of enzymes that sense curvature. Changes in genes for membrane-bending proteins, including myotubularin, amphiphysin-2, and dynamin-2, can cause centronuclear myopathies, a group of neuromuscular disorders.

How Proteins Shape Cell Membranes

what are membranes?

Membrane Receptors and Cell Signals

The plasma membrane sets the outer boundary of a cell and helps control how the cell interacts with its environment. It lets some substances enter, keeps others out, and releases some materials in controlled amounts. The membrane also needs to stay flexible so cells such as red and white blood cells can change shape as they move through narrow capillaries. The membrane surface also carries markers that help cells recognize one another. This recognition is important during early development,...

membrane fluidity

How Cell Membranes Stay Flexible

Cell membranes stay flexible because of the fluid mosaic model. The plasma membrane is a mosaic of phospholipids, cholesterol, proteins, and carbohydrates. These parts are separate but loosely attached, so the membrane keeps a fluid character. The membrane is still fairly rigid, but it can flow and self-seal after a very fine needle passes through it. Phospholipid tails also affect membrane fluidity. Saturated fatty acids in phospholipids have straight tails because they are packed with...

fluid mosaic model

Fluid Mosaic Model of the Membrane

The fluid mosaic model explains the structure and function of the plasma membrane. Scientists first identified the plasma membrane in the 1890s, and by 1915 they had identified its main chemical parts: lipids and proteins. Early electron micrographs showed a railroad track pattern, which helped lead to the first widely accepted membrane model in 1935.

membrane lipids

Membrane Lipids in Cells and Tissues

Membrane lipids give biological membranes their structure and help set their properties. In mammalian cells, lipids make up about 50% of the membrane on average. The amount can be much lower in the inner mitochondrial membrane or much higher in the myelin sheath around nerve cells. Several phospholipids are common in mammalian membranes. These include phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin. At physiological pH, phosphatidylserine carries a negative...

asymmetric lipid bilayer

Membrane Lipid Unevenness

Biological membranes have an uneven mix of lipids between the inner and outer layers. This membrane asymmetry gives each side a different chemical makeup and supports different cell functions. Evidence for this uneven layout came from treating an erythrocyte membrane with phospholipase. Phospholipase is an enzyme that breaks lipids into fatty acids and hydrophilic groups. It acted only on the outer layer, while the inner layer stayed intact. The treatment degraded about 80% of total membrane...

membrane asymmetry regulating transporters

membrane-asymmetry-regulating-transporters

Membrane Lipid Flipping and Transport

Membrane lipid flipping and transport help cells keep an uneven, or asymmetric, distribution of phospholipids across the membrane. This balance is controlled by flippase, floppase, and scramblase enzymes, which move lipids between the two membrane leaflets. Flippases move specific phospholipids from the outer leaflet to the inner leaflet. In eukaryotes, these enzymes are type-IV P-type ATPases, also called P4-ATPases. They are membrane pumps that use ATP and contain one transmembrane domain...

membrane carbohydrates

Membrane Sugars and Cell Identity

Membrane carbohydrates help give cells their surface identity and support plasma membrane function. The plasma membrane is a dynamic barrier made of lipids, proteins, and carbohydrates. These sugar chains have unique structural and chemical traits that help the membrane work properly for cell growth and survival. Membrane carbohydrates do not have a hydrophobic region, so they are found only on the outer surface of the cell. Sugar addition, or glycosylation, of proteins occurs in the lumens of...

membrane proteins

Facilitated Transport Across Cell Membranes

Facilitated transport uses membrane proteins to help materials cross the plasma membrane. These integral transmembrane proteins act as channels or carriers. They move selected substances through the membrane more easily than the lipid layer alone would allow. Channel proteins provide a hydrophilic, or water-friendly, path through the membrane. Their core forms a hydrated opening that lets solutes pass between the inside and outside fluids of the cell. This helps polar compounds avoid the...

lipids as anchors

Lipid Anchors in Membrane Proteins

Lipid anchors help attach proteins to the plasma membrane. In eukaryotic cells, the main lipid anchors are prenyl groups, fatty acyl groups, and glycosylphosphatidylinositol, or GPI, groups. Prenyl and fatty acyl groups anchor proteins on the cytosolic side of the membrane. GPI anchors proteins on the extracellular side. Prenylated proteins often have a CaaX motif at the carboxy terminus. In this sequence, C means cysteine, a means any aliphatic amino acid, and X means any other amino acid...

single-pass transmembrane proteins

How Membrane Proteins Span Cell Membranes

Membrane proteins help cells communicate, send signals, stick to other cells, and move molecules across the membrane. Integral membrane proteins are tightly linked to the cell membrane and carry out these jobs. Some integral membrane proteins sit only in one membrane layer. Fatty acid amide hydrolase is one example, and it is found on the cytoplasmic side of the membrane monolayer. Other integral membrane proteins are transmembrane proteins, which span across the membrane. These proteins have...

multi-pass transmembrane proteins and &#946;-barrels

multi-pass-transmembrane-proteins-and-barrels

Membrane-Spanning Helices and β-Barrels

Membrane-spanning proteins can cross the cell membrane more than once. Their transmembrane chain usually folds into either an alpha-helix or a beta-strand. Alpha-helix multi-pass proteins are common, while beta-strand proteins are found mainly in gram-negative bacteria, mitochondria, and chloroplasts. Some multi-pass alpha-helix proteins are G-protein-linked receptors, or GPCRs, and bacteriorhodopsin. GPCRs have seven transmembrane alpha-helices. Each receptor also has its own extracellular...

detergent purification of membrane proteins

detergent-purification-of-membrane-proteins

How Detergents Solubilize Membrane Proteins

Detergents help solubilize membrane proteins so they can be purified from the lipid bilayer. Their hydrophobic region can replace membrane phospholipids and keep integral membrane proteins in solution. A detergent works well only when its monomers reach the critical micelle concentration, or CMC. At that point, the molecules assemble into micelles, which are small clusters of detergent. Above the CMC, free detergent monomers stay in equilibrium with the micelles. The CMC varies with the...

protein diffusion in the membrane

How Membrane Proteins Move Side to Side

Membrane proteins can move across the cell surface by lateral diffusion, and they can also rotate in place. Scientists confirmed lateral movement with a cell fusion experiment. Mouse and human cells were fused to make hybrid cells. The membrane proteins on the two cells were tagged with red and green fluorescent markers. At first, each color stayed on its own side of the fused cell. After 40 minutes, the colors mixed across the whole cell surface, showing that the proteins had moved laterally. <br...

membrane domains

Lipid Rafts and Sperm Membrane Regions

Membrane domains organize specific lipids and proteins in defined parts of a cell membrane. This arrangement supports cell signaling, adhesion, and other important cellular processes. These domains can vary in size, composition, function, and how long they last. Some membrane domains are built from proteins. The membrane can contain distinct protein groups that carry out a cell’s specific functions. A clear example is the plasma membrane of a human sperm cell, which has different proteins in...

mechanisms of membrane domain formation

How Cell Membranes Form Domains

Cell membranes form domains when lipids and proteins gather into distinct regions. These regions, or membrane domains, are shaped by different physical properties that help some molecules stay together while others move apart. Some domains form through protein-protein interactions. Others depend on specific lipids, such as sphingolipids and sterols. Large proteins, including bacteriorhodopsin, can also cluster and create visible membrane domains. Membrane proteins can be held in place by...

mechanisms of membrane-bending

Cell membranes can bend into many shapes because they are flexible and made of a fluid mosaic. That bending can be temporary, as in vesicles, or long-lasting, as in microvilli. Cells control the size, place, and time of membrane curvature. Membrane bending can start inside the membrane itself or from proteins attaching to it. Changes in lipid makeup can create curvature, and proteins can help by making the membrane asymmetric or by clustering certain lipids. The shape of integral proteins also...

key terms and concepts

Learn how lipids, BAR proteins, protein crowding, and the cytoskeleton bend cell membranes. See how curvature helps organelle shape, fusion, and scission.

How Proteins Shape Cell Membranes | JoVE K12

cell biology

JoVE Core - Biologia Celular ilustra processos celulares complexos em vídeos de animação fáceis de entender e, ao mesmo tempo, abrangentes. Esta coleção foca nos componentes e funções essenciais das células, incluindo organelas e membranas, transporte celular e energia celular. É complementado por vídeos de Cientistas em ação que demonstram a aplicação da biologia celular em experimentos de pesquisa do mundo real.

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9-12.B.1.2.a

How Proteins Shape Cell Membranes

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