Conformation of the gramicidin A transmembrane channel: A 13C nuclear magnetic resonance study of 13C-enriched gramicidin in phosphatidylcholine vesicles☆☆☆

摘要: Abstract We have determined the orientation and organization of channel-forming polypeptide antibiotic, gramicidin A, in phosphatidylcholine vesicles using 13 C nuclear magnetic resonance spectroscopy. This is first direct structural evidence demonstrating conformation molecule as found membranes. The models previously proposed for dimer channel differ surface localization N termini. N-terminal to helical has only termini on surfaces membrane, while C-terminal surfaces. Parallel antiparallel β-double helices both incorporated specific nuclei at used chemical shifts spin lattice relaxation time, T 1 , measurements determine accessibility these labels three paramagnetic probes. 1. (1) water-soluble thulium ion causes a large change shift choline methyl groups, but little or no fatty acid carbons even near carbonyl end. changes three- fourfold greater than those labels. 2. (2) manganous induces rate enhancement that less methyls; 2 3 also enhancements, low values are obtained distal end chain. label 3. (3) Phosphatidylcholine labeled with nitroxide one chain enhancements 12 head group. valine methyls highest any experiment, acetyl zero enhancement. All our results indicate C-terminus located membrane N-terminus buried deep within lipid bilayer. These findings strongly favor an dimer, originally by Urry (1971), major vesicles.