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

Una membrana tiene una curvatura positiva cuando se dobla hacia el lado interno o citoplasmático. Por el contrario, una membrana tiene una curvatura negativa si se dobla hacia el lado externo o extracelular.
Existen múltiples mecanismos que pueden causar la flexión de la membrana.
La flexión de la membrana inducida por lípidos se debe a la agregación asimétrica de lípidos específicos en la membrana.
Los lípidos con grupos de cabeza grandes inducen una curvatura positiva de la membrana, mientras que los lípidos con grupos de cabeza pequeños producen una curvatura de la membrana negativa.
El andamiaje de proteínas es otro mecanismo en el que las proteínas deforman la membrana o estabilizan una membrana ya deformada.
En un mecanismo diferente, los dominios de proteínas hidrofóbicas se insertan de forma reversible en una capa de la membrana para aumentar su área en comparación con la otra capa. Esta asimetría obliga a la membrana a doblarse.
Finalmente, las fuerzas de empuje y tracción generadas por el ensamblaje y desensamblaje del citoesqueleto y sus proteínas motoras asociadas también pueden doblar la membrana para formar proyecciones, como los filopodios en las células epiteliales.

mecanismos de curvatura de la membrana

Las membranas vivas son flexibles debido a su naturaleza de mosaico fluido; sin embargo, su curvatura en diferentes formas es un proceso activo regulado por lípidos y proteínas específicos. La curvatura de la membrana puede ser transitoria como se ve en las vesículas o estable durante mucho tiempo como en las microvellosidades. Las células regulan el tamaño, la ubicación y la duración de la curvatura de la membrana.

La curvatura de la membrana puede ocurrir debido a cambios intrínsecos en la composición de los lípidos o a una asociación extrínseca con diferentes proteínas. Las proteínas implicadas en la creación de asimetría de la membrana o la agrupación de lípidos específicos desempeñan un papel esencial en la curvatura de la membrana inducida por los lípidos. La forma de las proteínas integrales también puede afectar la curvatura de la membrana. Por ejemplo, las proteínas transmembrana de forma cónica o cónica inversa producen curvatura en la membrana. La inserción de proteínas anfipáticas, como la epsina, en una de las capas también provoca la curvatura de la membrana.

Las proteínas curvadas como Bin/anfifisina/Rvs o las proteínas dímeras BAR crean una curvatura positiva de la membrana, mientras que la proteína BAR inversa o I-BAR induce una curvatura negativa en la membrana. Las proteínas BAR también insertan su dominio hidrofóbico en la membrana, lo que aumenta aún más la curvatura de la membrana. Además de los mecanismos bien-establecidos, el apiñamiento de proteínas es un mecanismo descubierto recientemente para la curvatura de la membrana donde la presión lateral generada por las interacciones proteína-proteína impulsa la curvatura de la membrana. Los citoesqueletos también desempeñan un papel importante en la curvatura de las membranas, y las fuerzas que generan son responsables de la morfología de algunos orgánulos como el retículo endoplásmico y el aparato de Golgi.

Los orgánulos celulares como el retículo endoplásmico, el aparato de Golgi y las mitocondrias tienen membranas intrincadamente plegadas; Estos plegados son esenciales para su funcionamiento. La curvatura de la membrana también es necesaria para la escisión de la membrana, la fusión de la membrana y la activación de la enzima que detecta la curvatura de la membrana. Las mutaciones en genes que producen proteínas que curvan la membrana, como miotubularina, anfifisina-2 y dinamina-2, pueden provocar un grupo de trastornos neuromusculares conocidos como miopatías centronucleares.

Mecanismos de curvatura de la membrana

Las membranas vivas son flexibles debido a su naturaleza de mosaico fluido; Sin embargo, su flexión en diferentes formas es un proceso activo regulado por ...

Education

Educación

JoVE Core

Cell Biology

Biología Celular

Unit 1

Unidad 1

Membrane Structure and Components

Estructura y componentes de la membrana

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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 Biología Celular ilustra procesos celulares complejos mediante completos vídeos animados fáciles de entender. Esta colección se centra en los componentes esenciales de las células y su funcionamiento, incluyendo los orgánulos y las membranas, el transporte celular y el metabolismo energético celular. Todo este material se complementa con los vídeos de científicos en acción, que muestran la aplicación de la biología celular en experimentos reales de investigación.

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9-12.B.1.1

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Co-activators and Co-repressors

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9-12.B.1.2

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9-12.B.1.2.a

How Proteins Shape Cell Membranes

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