Integral monotopic protein

Integral monotopic proteins are permanently attached to the cell membrane from one side, and are a type of integral membrane protein (IMP).

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)

Three-dimensional structures of the following integral monotopic proteins have been determined:

• prostaglandin H2 syntheses 1 and 2 (cyclooxygenases)
• lanosterol synthase and squalene-hopene cyclase
• microsomal prostaglandin E synthase
• carnitine O-palmitoyltransferase 2
• Phosphoglycosyl transferase C

There are also structures of integral monotopic domains of transmembrane proteins:

• monoamine oxidases A and B
• fatty acid amide hydrolase
• mammalian cytochrome P450 oxidases
• corticosteroid 11-beta-dehydrogenases