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Related Experiment Videos

Gramicidin tryptophans mediate formamidinium-induced channel stabilization

S A Seoh1, D Busath

  • 1Department of Physiology, Brown University, Providence, Rhode Island 02912, USA.

Biophysical Journal
|June 1, 1995
PubMed
Summary

Formamidinium ions stabilize gramicidin A channels, but this effect depends on tryptophan side chains. Replacing tryptophans with phenylalanines eliminates stabilization and associated electrical properties, indicating tryptophan

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Area of Science:

  • Biophysics
  • Membrane protein stabilization
  • Ion channel function

Background:

  • Formamidinium ions stabilize gramicidin A channels in lipid bilayers.
  • This stabilization effect is also observed in N-acetyl gramicidin channels.
  • The precise mechanism of formamidinium-mediated stabilization is not fully understood.

Purpose of the Study:

  • To investigate the role of tryptophan side chains in formamidinium-induced gramicidin A channel stabilization.
  • To elucidate the molecular basis of formamidinium interactions with gramicidin A channels.
  • To determine how tryptophan modifications affect channel electrophysiology and noise.

Main Methods:

  • Electrophysiological measurements using gramicidin analogs with tryptophan-to-phenylalanine substitutions (gramicidin M-).

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  • Comparison of channel behavior in monoolein and monoolein ether lipid bilayers.
  • Analysis of current-voltage relationships, channel lifetime, and open-channel noise.

    • Main Results:

    • Formamidinium-induced stabilization was eliminated in gramicidin M- where all four tryptophans were replaced by phenylalanines.
    • Tryptophan residues 9, 13, and 15 are crucial for stabilization; Trp-11 plays a minor role.
    • Formamidinium-dependent current-voltage supralinearity and open-channel noise were absent in gramicidin M-.

    Conclusions:

    • Formamidinium-induced gramicidin A channel stabilization is mediated by tryptophan side chains.
    • Specific tryptophan residues (9, 13, 15) cooperate to mediate this effect.
    • Formamidinium interactions with tryptophans influence channel lifetime, electrical properties, and noise, likely via water or lipid headgroup interactions.