Membrane protein

Membrane proteins are a type of protein that interact with, or are part of, biological membrane. They include integral membrane proteins that are permanently anchored or part of the membrane and peripheral membrane proteins that are only temporarily attached to the lipid bilayer or to other integral proteins. The integral proteins are typically transmembrane proteins, which span across the membrane.

Function

Membrane proteins perform a variety of functions vital to the survival of organisms:

• Ion channels: These proteins form pores that allow specific ions to pass through the membrane in response to certain stimuli.
• Transporters: These proteins transport chemicals and nutrients across the membrane.
• Receptors: These proteins receive chemical signals from outside the cell and initiate a response inside the cell.
• Cell adhesion molecules: These proteins bind cells together.

Structure

Membrane proteins have unique structures that allow them to function in the challenging environment of the lipid bilayer. They are typically composed of alpha helices or beta sheets that span the membrane and form a pore, or they may have a lipid anchor that tethers them to the membrane.

Types

There are two main types of membrane proteins:

• Integral membrane proteins: These proteins are permanently attached to the membrane. They can either span the entire membrane (transmembrane proteins) or be attached to only one side of the membrane (lipid-anchored proteins).
• Peripheral membrane proteins: These proteins are temporarily attached to the membrane or to other proteins. They can be located on either the inside or the outside of the cell.

See also

• Lipid bilayer
• Protein structure
• Cell membrane

Membrane_protein

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  Thylakoid membrane
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  Polytopic membrane protein
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  Monotopic membrane protein