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Related Experiment Videos

The alpha helix dipole: screened out?

Durba Sengupta1, Raghu Nath Behera, Jeremy C Smith

  • 1IWR-Computational Molecular Biophysics, University of Heidelberg, Im Neuenheimer Feld 368, 69120 Heidelberg, Germany.

Structure (London, England : 1993)
|June 9, 2005
PubMed
Summary

Alpha helix dipoles in proteins are crucial for function but weakened by water. Calculations reveal helix length impacts dipole strength differently in transmembrane versus soluble proteins.

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Area of Science:

  • Biophysics
  • Computational Biology
  • Structural Biology

Background:

  • Aligned alpha helices possess a macroscopic dipole moment parallel to their axis, influencing protein folding and function.
  • In aqueous solutions, solvent reaction fields significantly counteract helix dipoles, reducing their effective strength compared to vacuum.

Purpose of the Study:

  • To calculate the net effective dipole moment (μeff) of alpha helices using atomic detail and continuum electrostatics.
  • To investigate how helix length, orientation, and protein environment affect the effective dipole moment in different contexts.

Main Methods:

  • Utilized atomic-detail models of alpha helices.
  • Employed Poisson-Boltzmann continuum electrostatics calculations to determine effective dipole moments.

Related Experiment Videos

  • Analyzed results for both vacuum and aqueous solution conditions.

    • Main Results:

    • Effective dipole moment (μeff) increases with helix length in vacuum.
    • Transmembrane helices exhibit a decrease in μeff with increasing helix length.
    • For soluble proteins, μeff is highly sensitive to helix orientation and position relative to the solvent.
    • Developed guidelines for estimating μeff strength via visual inspection of protein structures.

    Conclusions:

    • The effective dipole moment of alpha helices is highly context-dependent, varying significantly between vacuum, transmembrane, and soluble protein environments.
    • Helix length has opposing effects on μeff depending on whether the helix is embedded in a membrane or exposed to solvent.
    • Structural context, including orientation and position, is critical for determining the functional impact of alpha helix dipoles in proteins.