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Related Experiment Videos

Designing transmembrane alpha-helices that insert spontaneously.

W C Wimley1, S H White

  • 1Department of Physiology and Biophysics and the Program in Macromolecular Structure, University of California at Irvine, Irvine, California 92697-4560, USA.

Biochemistry
|April 12, 2000
PubMed
Summary

Researchers engineered a transmembrane peptide, TMX-1, to study membrane protein hydrophobicity. TMX-1 shows promising properties for measuring peptide insertion thermodynamics into lipid bilayers.

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Area of Science:

  • Biophysics
  • Membrane protein biophysics
  • Protein engineering

Background:

  • Accurate hydrophobicity scales for membrane proteins are crucial for understanding protein structure and function.
  • The thermodynamic cost of inserting peptide bonds into membrane cores remains a significant unknown.
  • Direct measurement of free energies of transfer for membrane-spanning helices is essential.

Purpose of the Study:

  • To design and characterize a transmembrane (TM) peptide (TMX-1) for measuring the free energies of transfer from water to membranes.
  • To assess the feasibility of engineering peptides with measurable monomeric water solubility and spontaneous insertion into lipid bilayers.
  • To investigate the thermodynamic cost of partitioning hydrogen-bonded peptide bonds into the membrane hydrocarbon core.

Main Methods:

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  • Design of TMX-1, a 31-residue peptide with a nonpolar core, N- and C-caps, and a polar C-terminus.
  • Spectroscopic techniques including fluorescence spectroscopy, fluorescence quenching, and circular dichroism (CD) spectroscopy.
  • Fluorescence resonance energy transfer (FRET) to quantify spontaneous insertion across vesicle membranes.

Main Results:

  • TMX-1 exhibited high apparent water solubility, attributed to aggregation, but partitioned strongly into lipid vesicles (POPC and POPG).
  • CD spectroscopy confirmed a strong preference for a transmembrane alpha-helical conformation in lipid environments.
  • FRET analysis demonstrated that at least 50% of TMX-1 spontaneously inserted across vesicle membranes, with reversible insertion in POPC vesicles.

Conclusions:

  • TMX-1 possesses key properties required for thermodynamic measurements of TM peptide insertion, despite aggregation challenges.
  • The study delineates experimental considerations for designing peptides that partition spontaneously and reversibly into membranes as monomers.
  • The successful design of TMX-1 suggests that overcoming challenges in thermodynamic measurements of membrane peptide partitioning is achievable.