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An asymmetric ion channel derived from gramicidin A
Author(s) -
Xie Xiulan,
AlMomani Lo'ay,
Reiß Philipp,
Griesinger Christian,
Koert Ulrich
Publication year - 2005
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2004.04531.x
Subject(s) - chemistry , crystallography , conformational isomerism , dimer , dihedral angle , ion , nuclear magnetic resonance spectroscopy , molecule , stereochemistry , hydrogen bond , organic chemistry
The biological ion channel gramicidin A (gA) was modified by synthetic means to obtain the tail‐to‐tail linked asymmetric gA‐derived dimer compound 3 . Single‐channel current measurements for 3 in planar lipid bilayers exhibit an Eisenman I ion selectivity for alkali cations. The structural asymmetry does not lead to an observable functional asymmetry. The structure of 3 in solution without and with Cs cations was investigated by 1 H‐NMR spectroscopy. In CDCl 3 /CD 3 OH (1 : 1, v/v), 3 forms a mixture of double‐stranded β‐helices. Upon addition of excess CsCl, the double‐stranded species are converted completely into one new conformer: the right‐handed single‐stranded β‐helix. A combination of DQF‐COSY and TOCSY was used for the assignment of the 1 H‐NMR spectrum of the Cs– 3 complex in CDCl 3 /CD 3 OH (1 : 1, v/v). A total of 69 backbone, 27 long‐range, and 64 side‐chain distance restraints were obtained from NOESY together with 25 φ and 14 χ 1 torsion angles obtained from coupling constants. These data were used as input for structure calculation with dyana built in sybyl 6.8. A final set of 11 structures with an average rmsd for the backbone of 0.45 Å was obtained (PDB: 1TKQ). The structure of the Cs– 3 complex in solution is equivalent to the bioactive channel conformation in the membrane environment.