Gramicidin

File:Gramicidin helices.svg

Structure of gramicidin helices.

Gramicidin is a group of antibiotic compounds produced by the bacterium Bacillus brevis. These compounds are notable for their ability to form channels in cell membranes, allowing the passage of cations and disrupting the ion gradient necessary for cell survival. Gramicidins are primarily used as topical antibiotics due to their toxicity when administered systemically.

Structure

Gramicidins are linear peptides composed of 15 amino acids. The most common form, gramicidin A, forms a beta-helical structure that spans the lipid bilayer of cell membranes. This structure is stabilized by hydrogen bonds and allows the formation of a dimer that creates a channel through which ions can pass.

Mechanism of Action

Gramicidins function by inserting themselves into the phospholipid bilayer of bacterial cell membranes. Once inserted, they form a channel that disrupts the electrochemical gradient by allowing the free passage of monovalent cations such as sodium and potassium. This disruption leads to the loss of membrane potential and ultimately results in cell death.

Clinical Use

Due to their ability to disrupt cell membranes, gramicidins are effective against a wide range of Gram-positive bacteria. However, their use is limited to topical applications, such as in eye drops and ear drops, because they can cause hemolysis of red blood cells if used systemically.

History

Gramicidin was one of the first antibiotics to be discovered and was isolated in the 1930s by René Dubos. It was one of the first antibiotics to be used clinically, paving the way for the development of other antibiotic treatments.

Related Pages

• Antibiotic
• Bacillus brevis
• Peptide
• Cell membrane
• Ion channel