Name: membrane proteins in liposome models
Uploaded: 2023-04-30T06:31:34.000Z
Duration: 7 min 5 s
Channel: JoVE

K12 Standards

new-york-state-science-learning-standards

New York State Science Learning Standards

High School

Life Science

Structure and Function

HS-LS1-3.

Reconstitution of Membrane Proteins

Reconstitution is the process of returning an isolated biomolecule to its original form or function. This is particularly useful for studying membrane proteins, which enable important cellular functions and affect the behavior of nearby lipids. To study the function of purified membrane proteins in situ, they must be reconstituted by integrating them into an artificial lipid membrane.
This video introduces membrane protein reconstitution concepts and related procedures, such as protein isolation using detergent, formation of artificial vesicles using lipids, incorporation of the isolated protein into the artificial vesicle, and separation of the detergent from the solution. Finally, two applications are covered: reconstitution of membrane transport proteins and reconstitution of light-harvesting proteins.&#160;

reconstitution of membrane proteins

Reconstitution is the process of returning an isolated biomolecule to its original form or function. This is particularly useful for studying membrane proteins, which enable important cellular functions and affect the behavior of nearby lipids. To study the function of purified membrane proteins in situ, they must be reconstituted by integrating them into an artificial lipid membrane.
This video introduces membrane protein reconstitution concepts and related procedures, such as protein isolation using detergent, formation of artificial vesicles using lipids, incorporation of the isolated protein into the artificial vesicle, and separation of the detergent from the solution. Finally, two applications are covered: reconstitution of membrane transport proteins and reconstitution of light-harvesting proteins.&#160;
<div class="chapter_text" id="script_0">
Reconstitution is the process of restoring an isolated biomolecule to its original form or functionality. This approach is often used when studying membrane proteins, which enable many important cellular processes and affect the behavior of neighboring lipids. However, the complexity of the cell environment makes membrane protein functions difficult to study in situ. The proteins can be extracted and purified, but their actual functions cannot be evaluated without a membrane. Therefore, isolated membrane proteins are reconstituted by integration into an artificial lipid membrane, such as a liposome. This video will introduce the principles of membrane protein reconstitution, a general reconstitution procedure, and a few applications in biochemistry.
</div>
<div class="chapter_text" id="script_1">
Cell membranes primarily consist of phospholipids and membrane proteins. The phospholipids form a bilayer in which the hydrophilic phosphate heads interact with the aqueous interior and exterior of the cell, while the hydrophobic fatty acid tails interact with each other in the bilayer.
Some membrane proteins only interact with the membrane by electrostatic or noncovalent interactions. Others, called &#39;integral proteins&#39;, are embedded in the lipid bilayer.
Like the bilayer, integral proteins have hydrophilic ends and a hydrophobic center, and are held in place by hydrophobic interactions. Integral proteins that span the entire membrane are known as &#39;transmembrane proteins&#39;.
The interactions between these proteins and the membrane are so strong that even lysing the cells will not separate them. A special surfactant called a detergent is used to extract the proteins. Similar to phospholipids, detergents have hydrophilic heads and lipophilic tails, and can enter the membrane freely.
Inside the membrane, the lipophilic tails of the detergent interact with the hydrophobic protein core. This surrounds the protein with a shell of the hydrophilic detergent heads, which disrupts the protein-lipid interactions.
The protein-detergent complex is now easily separated from the membrane. The detergent makes the complex soluble in aqueous solutions, and ready for reconstitution in an artificial membrane.
Proteins are often reconstituted in the membranes of liposomes, which are artificial vesicles. To prepare liposomes, dried lipids are hydrated and agitated to induce vesicle formation. When a detergent is added, it is incorporated into the liposome membranes.
To reconstitute the protein, the solubilized proteins and liposomes are combined, and then the detergent is removed from solution by dialysis or chemical adsorption. The proteins and liposomes rapidly assemble into proteoliposomes, so only the hydrophilic groups are exposed. The proteins then function as they would in a cell membrane, and can be investigated in isolation.
Now that we&#39;ve covered the basics of protein reconstitution, let&#39;s go over a protocol for reconstituting membrane proteins in liposomes.
</div>
<div class="chapter_text" id="script_2">
To begin isolating the membrane proteins, the cells are lysed. Unbroken cells are removed with centrifugation.
The supernatant is centrifuged at a higher speed to pellet the membranes. The pellet is re-suspended and a detergent is added to extract the proteins.
The remaining cell debris is removed by additional centrifugation. The protein is purified from the supernatant with column chromatography and then concentrated or purified further as needed.
To begin preparing the liposomes, a suspension of phospholipids in organic solvent is dried under nitrogen or argon.
The phospholipids are hydrated with hydration buffer, and the mixture is sonicated to finish creating the liposomes.
Detergent is added to solubilize the liposomes, which is then combined with the proteins.
The detergent is then removed by adsorption onto polystyrene beads, dialysis, or a detergent-binding column. The resulting proteoliposomes are ready to be purified and used in subsequent experiments.
</div>
<div class="chapter_text" id="script_3">
Now that you are familiar with the basics of a membrane protein reconstitution procedure, let&#39;s look at a few applications of protein reconstitution in biochemistry.
A membrane-transport protein was reconstituted to gain a clearer understanding of its transport mechanism. Its function post-reconstitution was verified with an efflux of iodide ions. Then, the transport activity was studied in the presence of various small molecule ion channel inhibitors and potentiators. In this way, the direct interactions of these small molecules with the transport protein could be studied.
Chlorophyll and carotenoid-binding membrane proteins in plants harvest light, promote charge separation, and mitigate light damage. By reconstituting these light-harvesting proteins, their folding dynamics and interaction with pigments can be studied. The light-harvesting proteins reconstituted with this technique had very similar optical properties to the native proteins. Fluorescence emission spectroscopy can then be used to study energy transfer from pigments to the reconstituted light-harvesting proteins.
</div>
<div class="chapter_text" id="script_4">
You&#39;ve just watched JoVE&#39;s video on reconstitution of membrane proteins. Reconstitution is a way to transfer important proteins to a cell mimic for further investigation. This video covered the principles of protein reconstitution, a reconstitution protocol, and a few applications in biochemistry. Thanks for watching!
</div>

Reconstitution is the process of returning an isolated biomolecule to its original form or function. This is particularly useful for studying membrane ...

Reconstitution is the process of restoring an isolated biomolecule to its original form or functionality. This approach is often used when studying membrane proteins, which enable many important cellular processes and affect the behavior of neighboring lipids. However, the complexity of the cell environment makes membrane protein functions difficult to study?in situ.?The proteins can be extracted and purified, but their actual functions cannot be evaluated without a membrane. Therefore, isolated membrane proteins are?reconstituted?by integration into an artificial lipid membrane, such as a liposome. This video will introduce the principles of membrane protein reconstitution, a general reconstitution procedure, and a few applications in biochemistry.Cell membranes primarily consist of phospholipids and membrane proteins. The phospholipids form a bilayer in which the hydrophilic phosphate heads interact with the aqueous interior and exterior of the cell, while the hydrophobic fatty acid tails interact with each other in the bilayer.Some membrane proteins only interact with the membrane by electrostatic or noncovalent interactions. Others, called 'integral proteins', are embedded in the lipid bilayer.Like the bilayer, integral proteins have hydrophilic ends and a hydrophobic center, and are held in place by hydrophobic interactions. Integral proteins that span the entire membrane are known as 'transmembrane proteins'.The interactions between these proteins and the membrane are so strong that even lysing the cells will not separate them. A special surfactant called a detergent is used to extract the proteins. Similar to phospholipids, detergents have hydrophilic heads and lipophilic tails, and can enter the membrane freely.Inside the membrane, the lipophilic tails of the detergent interact with the hydrophobic protein core. This surrounds the protein with a shell of the hydrophilic detergent heads, which disrupts the protein-lipid interactions.The protein-detergent complex is now easily separated from the membrane. The detergent makes the complex soluble in aqueous solutions, and ready for reconstitution in an artificial membrane.Proteins are often reconstituted in the membranes of liposomes, which are artificial vesicles. To prepare liposomes, dried lipids are hydrated and agitated to induce vesicle formation. When a detergent is added, it is incorporated into the liposome membranes.To reconstitute the protein, the solubilized proteins and liposomes are combined, and then the detergent is removed from solution by dialysis or chemical adsorption. The proteins and liposomes rapidly assemble into proteoliposomes, so only the hydrophilic groups are exposed. The proteins then function as they would in a cell membrane, and can be investigated in isolation.Now that we've covered the basics of protein reconstitution, let's go over a protocol for reconstituting membrane proteins in liposomes.To begin isolating the membrane proteins, the cells are lysed. Unbroken cells are removed with centrifugation.The supernatant is centrifuged at a higher speed to pellet the membranes. The pellet is re-suspended and a detergent is added to extract the proteins.The remaining cell debris is removed by additional centrifugation. The protein is purified from the supernatant with column chromatography and then concentrated or purified further as needed.To begin preparing the liposomes, a suspension of phospholipids in organic solvent is dried under nitrogen or argon.The phospholipids are hydrated with hydration buffer, and the mixture is sonicated to finish creating the liposomes.Detergent is added to solubilize the liposomes, which is then combined with the proteins.The detergent is then removed by adsorption onto polystyrene beads, dialysis, or a detergent-binding column. The resulting proteoliposomes are ready to be purified and used in subsequent experiments.Now that you are familiar with the basics of a membrane protein reconstitution procedure, let's look at a few applications of protein reconstitution in biochemistry.A membrane-transport protein was reconstituted to gain a clearer understanding of its transport mechanism. Its function post-reconstitution was verified with an efflux of iodide ions. Then, the transport activity was studied in the presence of various small molecule ion channel inhibitors and potentiators. In this way, the direct interactions of these small molecules with the transport protein could be studied.Chlorophyll and carotenoid-binding membrane proteins in plants harvest light, promote charge separation, and mitigate light damage. By reconstituting these light-harvesting proteins, their folding dynamics and interaction with pigments can be studied. The light-harvesting proteins reconstituted with this technique had very similar optical properties to the native proteins. Fluorescence emission spectroscopy can then be used to study energy transfer from pigments to the reconstituted light-harvesting proteins.You've just watched JoVE's video on reconstitution of membrane proteins. Reconstitution is a way to transfer important proteins to a cell mimic for further investigation. This video covered the principles of protein reconstitution, a reconstitution protocol, and a few applications in biochemistry. Thanks for watching!

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Chemistry

Biochemistry

membrane proteins in liposome models

Membrane proteins can be moved into liposome models so their function can be studied outside a cell. Reconstitution means restoring an isolated biomolecule to a working form. For membrane proteins, that usually means placing a purified protein into an artificial lipid membrane.

Cell membranes are made mainly of phospholipids and membrane proteins. The phospholipids form a bilayer with hydrophilic phosphate heads facing water and hydrophobic fatty acid tails facing inward. Some membrane proteins attach by noncovalent or electrostatic interactions, while integral proteins are embedded in the bilayer. Transmembrane proteins are integral proteins that span the full membrane, and their strong interactions with the membrane are not broken just by lysing cells.

Detergent is used to extract these proteins. Detergents have hydrophilic heads and lipophilic tails, so they can enter the membrane. Their tails interact with the hydrophobic protein core and surround it with detergent heads, which breaks protein-lipid interactions. The protein-detergent complex becomes soluble in water and is ready for reconstitution.

Liposomes are artificial vesicles often used for this step. They are made by hydrating dried lipids and agitating them to form vesicles. When detergent is added, it becomes part of the liposome membrane. The purified protein and liposomes are then mixed, and the detergent is removed by dialysis or chemical adsorption. As the detergent leaves, the protein and lipids assemble into proteoliposomes, with hydrophilic groups exposed to water. The reconstituted proteins can then work in a membrane-like setting and be studied in isolation.

A general liposome protocol starts with cell lysis. Unbroken cells are removed by centrifugation, and the membranes are pelleted at higher speed. The pellet is resuspended, detergent is added to extract the proteins, and more centrifugation removes leftover debris. The protein is then purified by column chromatography and concentrated if needed.

Liposome preparation follows a separate path. Phospholipids in organic solvent are dried under nitrogen or argon, then hydrated with buffer. Sonication finishes the liposome formation. After detergent is added to solubilize the liposomes, the proteins are combined with them. The detergent is removed with polystyrene beads, dialysis, or a detergent-binding column, leaving proteoliposomes that can be purified and used in later experiments.

Reconstituted membrane proteins have several uses in biochemistry. One transport protein was reconstituted to better understand how it moves molecules. Its activity was checked by the efflux of iodide ions. Researchers also tested small-molecule ion channel inhibitors and potentiators to study how they interact with the transport protein directly.

Plant light-harvesting proteins are another example. These chlorophyll- and carotenoid-binding membrane proteins help harvest light, support charge separation, and reduce light damage. After reconstitution, scientists can study folding dynamics and pigment interactions. The reconstituted proteins showed optical properties very similar to native proteins, and fluorescence emission spectroscopy can be used to follow energy transfer from pigments to the proteins.

Membrane Proteins in Liposome Models

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Membrane proteins can be moved into liposome models so their function can be studied outside a cell. Reconstitution means restoring an isolated biomolecule to a working form. For membrane proteins, that usually means placing a purified protein into an artificial lipid membrane. Cell membranes are made mainly of phospholipids and membrane proteins. The phospholipids form a bilayer with hydrophilic phosphate heads facing water and hydrophobic fatty acid tails facing inward. Some membrane...

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See how membrane proteins are extracted with detergent and reinserted into liposomes so students can study transport and light-harvesting function.

Membrane Proteins in Liposome Models | JoVE K12

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HS-LS1-1.

Membrane Proteins in Liposome Models

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