Membrane protein
![Crystal structure of Potassium channel Kv1.2/2.1 Chimera. Calculated hydrocarbon boundaries of the lipid bilayer are indicated by red and blue dots.](/Images/godic/202412/22/2r9r_opm5116.png")
![Schematic representation of transmembrane proteins:
1. a single transmembrane α-helix (bitopic membrane protein)
2. a polytopic transmembrane α-helical protein
3. a polytopic transmembrane β-sheet protein
The membrane is represented in light-brown.](/Images/godic/202412/22/Polytopic_membrane_protein5116.png")
![Schematic representation of the different types of interaction between monotopic membrane proteins and the cell membrane:
1. interaction by an amphipathic α-helix parallel to the membrane plane (in-plane membrane helix)
2. interaction by a hydrophobic loop
3. interaction by a covalently bound membrane lipid (lipidation)
4. electrostatic or ionic interactions with membrane lipids (e.g. through a calcium ion)](/Images/godic/202412/22/Monotopic_membrane_protein.svg5116.png")
Membrane proteins are proteins that interact with, or are part of, biological membranes. They include integral membrane proteins that are permanently anchored to the membrane and peripheral membrane proteins which are only temporarily attached to the lipid bilayer or to integral proteins. The integral membrane proteins are classified as transmembrane proteins that span across the membrane and integral monotopic proteins that are attached to only one side of the membrane. Membrane proteins are are a common type of proteins along with soluble globular proteins, fibrous proteins, and disordered proteins. They are targets of over 50% of all modern medicinal drugs. It is estimated that 20–30% of all genes in most genomes encode membrane proteins.