What defines a peripheral membrane protein?

A peripheral membrane protein is defined by its association with the membrane surface through non-covalent interactions. This type of protein does not span the lipid bilayer or embed itself within the membrane like integral membrane proteins. Instead, peripheral proteins typically attach to the exterior or interior surfaces of the membrane, often interacting with the polar head groups of the lipids or with integral proteins.

This characteristic allows them to have various functions such as providing structural support, facilitating cell signaling, or participating in the transport of molecules. Since they are not embedded or anchored within the membrane by covalent bonds, peripheral proteins can be more easily released from the membrane under certain conditions, highlighting their role as transient or regulatory components in various cellular processes.