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Raman ir spectroscopic study of gramicidin a conformations

Archives of Biochemistry & Biophysics 202(2): 639-649
Raman ir spectroscopic study of gramicidin a conformations
Raman scattering and IR spectroscopic techniques were used to study the vibrational spectrum and conformation of the membrane channel protein gramicidin A in the solid state, in organic solutions and, using Raman scattering only, in a phospholipid environment. The investigation includes measurements on head- and tail-group modified gramicidin A and a potassium thiocyanate-gramicidin A complex. Tentative identification of the molecular vibrations is proposed on the basis of the data on model compounds. The existence of 4 distinct conformations of the gramicidin A chain is established: conformation I present in the solid state, and CH3OH and CD3OD solutions; conformation II present in films cast from CHCl3 solution; conformation III present in (CH3)2SO and (CD3)2SO solutions at concentrations below 0.5 M gramicidin A; and conformation IV present in the potassium thiocyanate-gramicidin A complex. The data obtainable on a gramicidin A-phospholipid suspension indicate a gramicidin A conformation in this environment corresponding either to the conformation I or II. The details of the spectra in the amide I region are consistent with a .beta.-parallel H-bonded .pi.LD helix for conformational I, in terms of the polypeptide vibrational calculations of Nevskaya and co-workers. Conformation II is consistent with an antiparallel double-stranded .pi.LD helix, while conformations III and IV probably have .pi.-helical structures with larger channel diameters. The data on head- and tail-modified gramicidin A molecules indicate that their confrmations are only slightly different from that of gramicidin A in conformation I.

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Accession: 006255772

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