page_title: Gramicidin S
section_title: Structure and pharmacological effect
hierarchical_section_title: Gramicidin S / Structure and pharmacological effect
caption_attribution_description: English: Gramicidin S 3D model from crystal structure rendered in Mercury with elipsoids at 50% probability. See Ref: Stereochemistry of Protected Ornithine Side Chains of Gramicidin S Derivatives: X-ray Crystal Structure of the Bis-Boc-tetra-N-methyl Derivative of Gramicidin S Keiichi Yamada, Masafumi Unno, Kyoko Kobayashi, Hiroyuki Oku, Hatsuo Yamamura, Shuki Araki, Hideyuki Matsumoto, Ryoichi Katakai, and Masao Kawai J. Am. Chem. Soc.; 2002; 124(43) pp 12684 - 12688; (Article) DOI: 10.1021/ja020307t
context_page_description: Gramicidin S or Gramicidin Soviet is an antibiotic that is effective against some gram-positive and gram-negative bacteria as well as some fungi.
  It is a derivative of gramicidin, produced by the gram-positive bacterium Bacillus brevis. Gramicidin S is a cyclodecapeptide, constructed as two identical pentapeptides joined head to tail, formally written as cyclo(-Val-Orn-Leu-D-Phe-Pro-)₂. That is to say, it forms a ring structure composed of five different amino acids, each one used twice within the structure. Another interesting point is that it utilizes two amino acids uncommon in peptides: ornithine as well as the atypical stereoisomer of phenylalanine. It is synthesized by gramicidin S synthetase.
context_section_description: Gramicidin S differs from other gramicidin types in that it is a cationic cyclic decapeptide and has a structure of an anti-parallel beta-sheet. Gramicidin S molecule is amphiphilic, with hydrophobic amino acids (D-Phe, Val, Leu side chains) and charged aminoacid (L-Orn). It exhibits strong antibiotic activity towards Gram-negative and Gram-positive and even several pathogenic fungi. The mode of action is not entirely agreed upon, but it is generally accepted that it is disruption of the lipid membrane and enhancement of the permeability of the bacterial cytoplasmic membrane. Unfortunately, being hemolytic at even low concentrations, gramicidin S is only used as topical applications at present. Additionally, Gramicidin S has been employed as a spermicide and therapeutic for genital ulcers caused by sexually transmitted disease.
caption: Crystal structure of modified Gramicidin S. Modification includes Boc groups on the ornithine as well as methylation of select amide nitrogens to force cyclic conformation.[10]
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