Name: membrane lipid flipping and transport
Uploaded: 2023-04-30T10:41:36.000Z
Duration: 1 min 19 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

membrane-asymmetry-regulating-transporters

Membrane Asymmetry Regulating Transporters

L’asymétrie membranaire est régulée par trois types de transporteurs qui transloquent les phospholipides à travers la bicouche.
Les flippases sont des importateurs de lipides dépendants de l’ATP qui transfèrent la phosphatidylsérine et la phosphatidyléthanolamine de la couche externe à la couche interne.
Les floppases sont des exportateurs de lipides non spécifiques dépendants de l’ATP qui transportent les lipides de la couche interne vers la couche externe. La flippase et la floppase jouent toutes deux un rôle important dans la génération de l’asymétrie membranaire.
Les scramblases sont des transporteurs indépendants de l’ATP qui permettent le mouvement aléatoire des lipides dans les deux couches, réduisant ainsi l’asymétrie membranaire. Dans les érythrocytes, les scramblases sont inactives à des niveaux physiologiques normaux de calcium intracellulaire et s’activent lorsque la concentration d’ions calcium augmente. 
L’activation des scramblases peut transférer la phosphatidylsérine de la couche membranaire interne à la couche membranaire externe. L’exposition vers l’extérieur de la phosphatidylsérine marque les érythrocytes pour une mort suicidaire connue sous le nom d’éryptose et déclenche leur élimination par les macrophages.

transporteurs régulant l’asymétrie de la membrane

Des enzymes comme la flippase, la floppase et la scramblase transfèrent les phospholipides d'une couche à l'autre de la membrane, affectant ainsi l'asymétrie de la membrane.

Flippase

Les flippases eucaryotes sont des ATPases de type P de type IV ou des P4-ATPases appartenant aux protéines de la famille des ATPases de type P qui sont des pompes liées à la membrane impliquées dans le transport d'ions et de molécules médié par l'ATP à travers la membrane. Les flippases retournent des phospholipides spécifiques du feuillet externe vers le feuillet interne d'une membrane. Toutes les P4-ATPases ont un domaine transmembranaire contenant dix hélices α transmembranaires et trois domaines cytoplasmiques. Les trois domaines cytoplasmiques comprennent un domaine de liaison aux nucléotides, un domaine de phosphorylation et un domaine actionneur impliqué dans l'étape de déphosphorylation.

Floppase

Les floppases appartiennent à la cassette de liaison ATP ou aux protéines de la famille des transporteurs ABC qui transfèrent une variété de phospholipides du feuillet interne au feuillet externe d'une membrane. Certaines des protéines essentielles de cette famille sont ABCA1, ABCA4, ABCB1 et ABCB4. La floppase ABCA1 peut transférer le cholestérol du feuillet interne vers le feuillet externe de la membrane, et sa mutation peut entraîner la maladie de Tanger.

Scramblase

La Scramblase, contrairement à la flippase et à la floppase, peut effectuer le transfert bidirectionnel des phospholipides dans la membrane sans utiliser l'énergie de l'hydrolyse de l'ATP. Il existe deux types de scramblases dans la cellule : la protéine transmembranaire 16F (TMEM16F) et la protéine 8 liée à XK (Xkr8). La scramblase TMEM16F est située dans la membrane plaquettaire et nécessite une concentration élevée d’ions calcium pour son activation. En revanche, la caspase active Xkr8 dans la membrane cellulaire pendant l'apoptose. L'expression défectueuse de la scramblase entraîne un trouble de la coagulation appelé syndrome de Scott.

Transporteurs Régulant L’asymétrie de La Membrane

Des enzymes comme la flippase, la floppase et la scramblase transfèrent les phospholipides d’une couche à une autre de la membrane, affectant ainsi l’asymétrie membranaire.
...

Education

Enseignement

JoVE Core

Cell Biology

Biologie cellulaire

Unit 1

Unité 1

Membrane Structure and Components

Structure et composants de la membrane

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 with ten transmembrane alpha-helices and three cytoplasmic domains: a nucleotide-binding domain, a phosphorylation domain, and an actuator domain that helps with dephosphorylation.

Floppases move phospholipids in the opposite direction, from the inner leaflet to the outer leaflet. They belong to the ATP-binding cassette, or ABC-transporter, family. Important members include ABCA1, ABCA4, ABCB1, and ABCB4. ABCA1 can move cholesterol to the outer leaflet, and mutation of ABCA1 can lead to Tangier disease.

Scramblases work differently from flippases and floppases. They move phospholipids in both directions and do not use ATP hydrolysis for energy. Two scramblases found in cells are TMEM16F and Xkr8. TMEM16F is found in platelet membranes and needs a high calcium ion level for activation, while caspase activates Xkr8 during apoptosis. When scramblase expression is defective, it can cause the bleeding disorder Scott syndrome.

Membrane Lipid Flipping and Transport

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 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

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...

key terms and concepts

Learn how flippases, floppases, and scramblases move phospholipids across membranes and help maintain membrane asymmetry in cells.

Membrane Lipid Flipping and Transport | JoVE K12

cell biology

JoVE Core Biologie cellulaire illustre les processus cellulaires complexes dans des leçons vidéos complètes mais faciles à comprendre. Cette collection se concentre sur les composants et fonctions essentiels de la cellule ; cela inclut les organelles et les membranes ainsi que le transport et le métabolisme énergétique cellulaire. Elle est complétée par nos vidéos de scientifiques à l'action qui démontrent l'application de la biologie cellulaire dans des expériences concrètes.

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1. Engage in evidence-based argument to relate a cell's function to the structure, function, and diversity of its components. Examples: Muscle cells have a large number of mitochondria, which create energy for contraction in the form of ATP. Some plant cells have a large vacuole which is used for storage and transport of excess nutrients in changing environments.

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9-12.B.1.2.a

Membrane Lipid Flipping and Transport

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