The Conducting Form of Gramicidin a is a Right-Handed Double-Stranded Double Helix.
Burkhart, B.M., Li, N., Langs, D.A., Pangborn, W.A., Duax, W.L.(1998) Proc Natl Acad Sci U S A 95: 12950
- PubMed: 9789021 
- DOI: https://doi.org/10.1073/pnas.95.22.12950
- Primary Citation of Related Structures:  
1AV2, 1BDW - PubMed Abstract: 
The linear pentadecapeptide antibiotic, gramicidin D, is a naturally occurring product of Bacillus brevis known to form ion channels in synthetic and natural membranes. The x-ray crystal structures of the right-handed double-stranded double-helical dimers (DSDH) reported here agree with 15N-NMR and CD data on the functional gramicidin D channel in lipid bilayers. These structures demonstrate single-file ion transfer through the channels. The results also indicate that previous crystal structure reports of a left-handed double-stranded double-helical dimer in complex with Cs+ and K+ salts may be in error and that our evidence points to the DSDH as the major conformer responsible for ion transport in membranes.
Organizational Affiliation: 
Hauptman-Woodward Medical Research Institute, Inc., 73 High Street, Buffalo, NY 14203, USA. burkhart@hwi.buffalo.edu