the protein-membrane interactions

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Copyright © 2003 Nicolas Sapay
last modified : apr 2006
wabmaster: n.sapay

polytopic membrane proteins

The membrane proteins can be divided into two categories : the polytopic proteins and the monotopic proteins. Polytopic proteins are in contact with the two compartments defined by the membrane. Their can contains :
- A. transmembrane α-helices.
- B. transmembrane β-strands
A transmembrane protein can include 1 to more than 20 transmembrane segments. If it contains transmembrane β-strands, the protein have to be conformed in a β-barrel, creating a pore through the membrane. One β-barrel can include 6 to 22 β-strands.
monotopic membrane proteins

The monotopic proteins are in contact with only one of the two compartments defined by the membrane. Their membrane segments are more heteroclite and can include :
- C. one or more amphipathic in-plane α-helices, e.g. the NS5A protein from the hepatitis C virus
- D. hydrophobic loops, e.g. the snake cardiotoxin
- E. covalent links with hydrophobic compounds (glycosyl-inositol-phosphate, palmitate, ...)
- F. electrosatic bonds with phospholipids headgroups, e.g. annexin V. Additional ions (e.g. Ca2+) can be required for the binding.
A monotopic protein can include several type of membrane segments. Polytopic proteins can also contain monotopic membrane segment. For example, the protein Vpu from the HIV include 1 transmembrane helix and 2 in-plane amphipathic helices.