Abstract
The original proposed structure and transport mechanism of the Gramicidin A transmembrane channel are reviewed, as are the structural issues to be resolved in proving the structure in the membrane. The proposed structural elements of (1) the single-stranded β6.33,3 helix, (2) the association of amino end to amino end by hydrogen bonding, and (3) the left-handed helix sense have been confirmed. Two binding sites related by twofold symmetry and separated by just over 20 A have been observed, and a free-energy profile for sodium ion permeation through the channel has been obtained. A comparison of 1-13C-L-tryptophanyl chemical shifts induced by sodium ions and by barium ions demonstrates the barium ion binding to the mouth of the channel with a location displaced toward the aqueous solution. With the nuclear magnetic resonance observed rapid exchange between the barium ion binding site and the solution it is concluded that the central barrier, due to the positive image force of the lipid surrounding the channel, prevents divalent ion permeability.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
