Membrane protein

Peripheral proteins dissociate following treatment with a polar reagent, such as a solution with an elevated pH or high salt concentrations.

[citation needed] Integral and peripheral proteins may be post-translationally modified, with added fatty acid, diacylglycerol[8] or prenyl chains, or GPI (glycosylphosphatidylinositol), which may be anchored in the lipid bilayer.

Polypeptide toxins and many antibacterial peptides, such as colicins or hemolysins, and certain proteins involved in apoptosis, are sometimes considered a separate category.

These proteins are water-soluble but can undergo significant conformational changes, form oligomeric complexes and associate irreversibly or reversibly with the lipid bilayer.

[12] In humans, current thinking suggests that fully 30% of the genome encodes membrane proteins.

Membrane protein complexes of photosynthesis in the thylakoid membrane
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.
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 )