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. 1988 May;53(5):689–695. doi: 10.1016/S0006-3495(88)83150-3

Low conductance gramicidin A channels are head-to-head dimers of beta 6.3-helices.

D Busath 1, G Szabo 1
PMCID: PMC1330247  PMID: 2455548

Abstract

Weakly conductive, atypical channels were observed to form from highly purified Val1-gramicidin A in planar lipid bilayer membranes. The structure of these low-conductance channels (minis) was investigated by a detailed study of their channel forming characteristics. The possibility that minis originate from primary structural analogs or degradation products of gramicidin was considered and ruled out. In particular, spontaneous conductance changes in single channels demonstrated that minis can derive directly and reversibly from "standard" channels having the most common conductance level. The fraction of channels which are minis does not vary with changes in membrane gramicidin concentration, indicating that mini and standard channels have the same molecularity, that is, both are dimers. The mean lifetime of mini channels is only slightly shorter than that of standard channels, indicating that the six hydrogen bonds that stabilize the head-to-head dimer are minimally affected in minis. The fraction of channels which are minis is unaffected by the ionic strength, ionic composition, or pH of the bathing solution; it is also unaffected by the lipid composition of the bilayer. These findings are consistent with the hypothesis that minis arise from minor changes in the conformation of the Val1-gramicidin A molecule near the channel entrance or exit.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Bamberg E., Apell H. J., Alpes H., Gross E., Morell J. L., Harbaugh J. F., Janko K., Läuger P. Ion channels formed by chemical analogs of gramicidin A. Fed Proc. 1978 Oct;37(12):2633–2638. [PubMed] [Google Scholar]
  2. Bamberg E., Noda K., Gross E., Läuger P. Single-channel parameters of gramicidin A,B, and C. Biochim Biophys Acta. 1976 Jan 21;419(2):223–228. doi: 10.1016/0005-2736(76)90348-5. [DOI] [PubMed] [Google Scholar]
  3. Busath D. D., Andersen O. S., Koeppe R. E., 2nd On the conductance heterogeneity in membrane channels formed by gramicidin A. A cooperative study. Biophys J. 1987 Jan;51(1):79–88. doi: 10.1016/S0006-3495(87)83313-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Busath D., Szabo G. Atypical gramicidin a channels appear to have increased field strength at one binding site. Biophys J. 1984 Jan;45(1):85–87. doi: 10.1016/S0006-3495(84)84118-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Busath D., Szabo G. Gramicidin forms multi-state rectifying channels. Nature. 1981 Nov 26;294(5839):371–373. doi: 10.1038/294371a0. [DOI] [PubMed] [Google Scholar]
  6. Busath D., Szabo G. Permeation characteristics of gramicidin conformers. Biophys J. 1988 May;53(5):697–707. doi: 10.1016/S0006-3495(88)83151-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Hladky S. B., Haydon D. A. Ion transfer across lipid membranes in the presence of gramicidin A. I. Studies of the unit conductance channel. Biochim Biophys Acta. 1972 Aug 9;274(2):294–312. doi: 10.1016/0005-2736(72)90178-2. [DOI] [PubMed] [Google Scholar]
  8. Kolb H. A., Bamberg E. Influence of membrane thickness and ion concentration on the properties of the gramicidin a channel. Autocorrelation, spectral power density, relaxation and single-channel studies. Biochim Biophys Acta. 1977 Jan 4;464(1):127–141. doi: 10.1016/0005-2736(77)90376-5. [DOI] [PubMed] [Google Scholar]
  9. Mazet J. L., Andersen O. S., Koeppe R. E., 2nd Single-channel studies on linear gramicidins with altered amino acid sequences. A comparison of phenylalanine, tryptophane, and tyrosine substitutions at positions 1 and 11. Biophys J. 1984 Jan;45(1):263–276. doi: 10.1016/S0006-3495(84)84153-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Ovchinnikov Y. A. Physico-chemical basis of ion transport through biological membranes: ionophores and ion channels. Eur J Biochem. 1979 Mar;94(2):321–336. doi: 10.1111/j.1432-1033.1979.tb12898.x. [DOI] [PubMed] [Google Scholar]
  11. Prasad K. U., Trapane T. L., Busath D., Szabo G., Urry D. W. Synthesis and characterization of (1-13C) Phe9 gramicidin A. Effects of side chain variations. Int J Pept Protein Res. 1983 Sep;22(3):341–347. doi: 10.1111/j.1399-3011.1983.tb02100.x. [DOI] [PubMed] [Google Scholar]
  12. Prasad K. U., Trapane T. L., Busath D., Szabo G., Urry D. W. Synthesis and characterization of 1-(13) C-D X Leu12, 14 gramicidin A. Int J Pept Protein Res. 1982 Feb;19(2):162–171. [PubMed] [Google Scholar]
  13. Rudnev V. S., Ermishkin L. N., Fonina L. A., Rovin YuG The dependence of the conductance and lifetime of gramicidin channels on the thickness and tension of lipid bilayers. Biochim Biophys Acta. 1981 Mar 20;642(1):196–202. doi: 10.1016/0005-2736(81)90149-8. [DOI] [PubMed] [Google Scholar]
  14. Stark G., Strässle M., Takácz Z. Temperature-jump and voltage-jump experiments at planar lipid membranes support an aggregational (micellar) model of the gramicidin A ion channel. J Membr Biol. 1986;89(1):23–37. doi: 10.1007/BF01870893. [DOI] [PubMed] [Google Scholar]
  15. Szabo G. Structural aspects of ionophore function. Fed Proc. 1981 Jun;40(8):2196–2201. [PubMed] [Google Scholar]
  16. Urry D. W., Alonso-Romanowski S., Venkatachalam C. M., Trapane T. L., Prasad K. U. The source of the dispersity of gramicidin A single-channel conductances. The L X Leu5-gramicidin A analog. Biophys J. 1984 Aug;46(2):259–265. doi: 10.1016/S0006-3495(84)84019-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Urry D. W., Goodall M. C., Glickson J. D., Mayers D. F. The gramicidin A transmembrane channel: characteristics of head-to-head dimerized (L,D) helices. Proc Natl Acad Sci U S A. 1971 Aug;68(8):1907–1911. doi: 10.1073/pnas.68.8.1907. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Urry D. W., Long M. M., Jacobs M., Harris R. D. Conformation and molecular mechanisms of carriers and channels. Ann N Y Acad Sci. 1975 Dec 30;264:203–220. doi: 10.1111/j.1749-6632.1975.tb31484.x. [DOI] [PubMed] [Google Scholar]
  19. Veatch W. R., Blout E. R. The aggregation of gramicidin A in solution. Biochemistry. 1974 Dec 17;13(26):5257–5264. doi: 10.1021/bi00723a002. [DOI] [PubMed] [Google Scholar]
  20. Veatch W. R., Fossel E. T., Blout E. R. The conformation of gramicidin A. Biochemistry. 1974 Dec 17;13(26):5249–5256. doi: 10.1021/bi00723a001. [DOI] [PubMed] [Google Scholar]
  21. Veatch W. R., Mathies R., Eisenberg M., Stryer L. Simultaneous fluorescence and conductance studies of planar bilayer membranes containing a highly active and fluorescent analog of gramicidin A. J Mol Biol. 1975 Nov 25;99(1):75–92. doi: 10.1016/s0022-2836(75)80160-4. [DOI] [PubMed] [Google Scholar]

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