Name: how membrane proteins span cell membranes
Uploaded: 2023-04-30T09:16:08.000Z
Duration: 1 min 25 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

Single-pass Transmembrane Proteins

Les protéines transmembranaires sont intégrées dans la bicouche lipidique et ont des domaines de chaque côté de la membrane en plus de leurs domaines transmembranaires. Ils constituent environ 25 % des protéines codées dans le génome humain et ont divers rôles, notamment des transporteurs, des enzymes et des récepteurs.
Le domaine transmembranaire, la région qui s’étend sur toute la membrane de la protéine, contient des acides aminés non polaires qui forment des sections hydrophobes. En revanche, les domaines cytosolique et exoplasmique sont souvent hydrophiles.
En fonction du nombre de fois que la chaîne polypeptidique traverse la membrane, les protéines transmembranaires peuvent être classées en protéines à passage unique ou à plusieurs passes.
Une protéine à passage unique contient environ 20 à 30 résidus d’acides aminés non polaires qui recouvrent la membrane. Cette passe est le plus souvent une hélice alpha positionnée verticalement ou obliquement dans la membrane.
Dans une hélice alpha, les groupes carbonyle et amide du squelette peptidique forment des liaisons hydrogène, tandis que les groupes latéraux non polaires pointent vers l’extérieur dans l’environnement hydrophobe de la membrane.
Les protéines à passage unique peuvent former des homo- ou hétéro-oligomères par des interactions non covalentes.

les protéines transmembranaires à passage unique

Les protéines membranaires intégrales sont étroitement associées à la membrane cellulaire et jouent un rôle crucial dans la communication cellulaire, la signalisation, l'adhésion et le transport des molécules. Certaines protéines membranaires intégrales ne sont présentes que dans la monocouche membranaire. Par exemple, l’enzyme amide hydrolase d’acide gras est présente du côté cytoplasmique de la monocouche membranaire. En revanche, un autre type de protéine membranaire intégrale, également connue sous le nom de protéine transmembranaire, s’étend à travers la membrane. Les protéines transmembranaires contiennent les domaines cytoplasmiques, transmembranaire et exoplasmique. Les protéines intégrées uniquement dans la membrane, sans domaine exoplasmique ou cytoplasmique, n’ont pas encore été découvertes.

Les protéines membranaires à passage unique, comme le récepteur tyrosine kinase, ne contiennent qu'un seul domaine transmembranaire en hélice α. Dans la majorité des protéines membranaires, le domaine transmembranaire est une hélice α contenant environ 20 à 30 acides aminés non polaires. Cette séquence d'acides aminés caractéristique dans l'hélice α des protéines transmembranaires est utilisée pour identifier les domaines transmembranaires potentiels présents dans une protéine à l'aide du tracé d'hydropathie. L'énergie libre nécessaire pour transférer un acide aminé d'un milieu aqueux à un milieu lipidique est utilisée pour générer le tracé d'hydropathie. Les valeurs énergétiques moyennes des segments polypeptidiques donnent des informations sur les domaines transmembranaires potentiels présents dans une protéine. Un tracé d'hydropathie peut aider à identifier si une protéine particulière est membranaire à passage unique ou à passages multiples.

Les protéines transmembranaires jouent un rôle essentiel dans l'interaction d'une cellule avec l'environnement extracellulaire. Les protéines transmembranaires sont donc la cible de plus de 50 % des médicaments disponibles et revêtent une grande importance pharmacologique. Une meilleure connaissance de la structure et de la fonction des protéines transmembranaires peut aider à comprendre la pathogenèse de plusieurs maladies et à découvrir des médicaments pertinents.

Les protéines transmembranaires à passage unique

Les protéines membranaires intégrales sont étroitement associées à la membrane cellulaire et jouent un rôle crucial dans la communication cellulaire, la signalisation, l’adhésion et le transport ...

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

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 cytoplasmic, transmembrane, and exoplasmic domains.

Single-pass membrane proteins are a type of transmembrane protein with only one transmembrane alpha-helix. Receptor tyrosine kinase is one example. In most membrane proteins, this transmembrane segment is an alpha-helix with about 20 to 30 non-polar amino acids. Proteins embedded only in the membrane, without exoplasmic or cytoplasmic domains, have not yet been discovered.

Scientists use a hydropathy plot to look for likely transmembrane regions in a protein. This plot is based on the free energy needed to move amino acids from water into a lipid environment. Average energy values along a polypeptide chain can point to possible membrane-spanning segments. A hydropathy plot can also help show whether a protein is single-pass or multi-pass.

Transmembrane proteins are important for how cells interact with the outside environment. Because of this, they are targets for more than 50% of available drugs. Their structure and function are important in understanding disease and supporting drug discovery.

How Membrane Proteins Span Cell Membranes

how-membrane-proteins-span-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

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 transmembrane proteins span cell membranes, how hydropathy plots identify membrane domains, and why these proteins matter in cell signaling and drug targets.

How Membrane Proteins Span Cell Membranes | 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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overview-of-myosin-structure-and-function

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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.

9-12.B.1.1

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Bacterial RNA Polymerase

Eukaryotic RNA Polymerases

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Transcription Elongation Factors

pre-mrna-processing-modification-of-pre-mrna-ends

Pre-mRNA Processing: Modification of pre-mRNA Ends

In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or ...

Pre-mRNA Processing: RNA Splicing

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Additional Subnuclear Structures

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regulation-of-expression-occurs-at-multiple-steps

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9-12.B.1.2

Nucleic Acids and Nucleotides

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9-12.B.1.2.a

How Membrane Proteins Span Cell Membranes

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