Non-ribosomally Synthesized Channels
Proteins belonging to this family form oligomeric trans-membrane channels. Voltage may induce channel formation by promoting assembly of the oligomeric pore-forming structure. These "depsipeptides" are often made by bacteria and fungi and are used as agents of biological warfare. Other substances, completely lacking amino acids, may also be involved in channel formation
Over 100 subgroups belong to the "Non-ribosomally Synthesized Channels" family, including amongst others:
The Gramicidin A (Gramicidin A) Channel Family
The Alamethicin or Peptaibol Antibiotic Channel-forming (Alamethicin) Family
The Saponin (Saponin) Family
The Ceramide-forming Channel (Ceramide) Family
Alamethicin Background Information
Alamethicin was the first isolated and is the best characterized member of the peptaibol class of natural linear depsipeptide antibiotics. It is a channel-forming peptide, produced by the fungus Trichoderma viride. As a member of the peptaibol peptide family, it contains the non-proteinogenic amino acid residue Aib (2-aminoisobutyric acid). It adopts helical secondary monomeric and dimeric helix-bend-helix structures that self assemble in membranes into ion conducting helix bundles.
Chemically, the peptaibol Alamethicin is a peptide of 20 amino acids and forms a alpha-helical structure. In cell membranes, it forms voltage-dependent ion channels by aggregation of four to six molecules.
Peptaibol compounds are characterized by acetylated N-termini, a high percentage of α-amino-isobutyrate (AIB), and a C-terminal amino alcohol. Most contain 18-20 residues. Because of their high proportion of AIB, they form α-helical structures. Voltage causes them to autoassociate to form ion channels. The alamethicin pore is of the barrel-stave type consisting of eight alamethicin helices. The channels formed conduct ions in a non-saturable fashion, suggesting that transport occurs in a diffusional process without ion binding at discrete sites in the channel. The channels are mildly cation-selective.
Bilayer Recordings on the Orbit Product family or on the Port-a-Patch
Reviews and Links
- Hancock et al. (1999) Peptide Antibiotics. Antimicrobial Agents and Chemotherapy. DOI: 10.1128/AAC.43.6.1317
Transporter classification database:
Data and Applications