Peripheral Membrane Proteins

Definition and Location

Peripheral membrane proteins are proteins that are temporarily associated with the lipid bilayer or with integral membrane proteins. They are not embedded within the hydrophobic core of the membrane but are found on the periphery (surface) of the lipid bilayer.

• Location: Associated with either the extracellular or intracellular side of the membrane.

• Attachment: Typically interact with the membrane via electrostatic interactions and hydrogen bonding.

• Association: May also interact with integral proteins or with polar head groups of phospholipids.

Properties and Functions

• Peripheral membrane proteins can be removed from the membrane by mild treatments, such as changes in pH or high salt concentrations, without disrupting the membrane's integrity.

• They play roles in cell signaling, maintaining cell shape, and as part of the cytoskeleton.

• They do not span the lipid bilayer.

Example: Membrane Structure

The diagram below illustrates the position of peripheral membrane proteins relative to the lipid bilayer and integral membrane proteins:

• Peripheral proteins: Located on the surface of the membrane (extracellular or intracellular side).

• Integral proteins: Span the membrane or are embedded within the lipid bilayer.

Practice: Key Points about Peripheral Membrane Proteins

• Can be released from the membrane by disrupting noncovalent interactions (e.g., with salt or pH changes).

• Do not require detergents for removal (unlike integral proteins).

• Are not covalently bound to membrane lipids or integral proteins.

• Commonly function as enzymes, structural proteins, or as part of signaling pathways.

Practice: Classification of Membrane Proteins

Additional info:

• Integral membrane proteins require detergents for extraction because they are embedded within the hydrophobic core of the membrane.

• Peripheral proteins are important for cellular communication and maintaining the structure of the cell membrane.