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Related Experiment Videos

Helix-coil transitions re-visited.

Harold A Scheraga1, Jorge A Vila, Daniel R Ripoll

  • 1Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithica, NY 14853-1301, USA. has5@cornell.edu

Biophysical Chemistry
|December 19, 2002
PubMed
Summary

The helix-coil transition in polyamino acids models amino acid helix formation. Introducing polar residues like lysine within a poly-L-alanine sequence can skew results, but random copolymers with neutral hosts offer accurate helix propensity data.

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Area of Science:

  • Biochemistry
  • Polymer Science
  • Protein Folding

Background:

  • The helix-coil transition in polyamino acids serves as a model for amino acid helix-forming propensities.
  • This model is less suitable for the two-state folding/unfolding transitions observed in globular proteins.

Purpose of the Study:

  • To summarize equilibrium and kinetic treatments of the helix-coil transition.
  • To investigate the influence of polar amino acid residues on the helix-forming tendency of poly-L-alanine.
  • To evaluate the reliability of different copolymer structures for determining amino acid helix propensities.

Main Methods:

  • Analysis of equilibrium and kinetic data for helix-coil transitions.
  • Modeling of polyamino acid copolymers, including poly-L-alanine, poly-L-lysine, and alanine/glutamine copolymers.

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  • Comparison of helix-forming tendencies in homopolymers and various copolymer architectures (triblock, random).

    • Main Results:

    • Incorporating polar residues like lysine as end groups in triblock copolymers minimally affects the central poly-L-alanine's helix tendency.
    • Embedding charged polar residues (lysine) within the alanine sequence leads to hydration effects that mask the alanine helix propensity.
    • Neutral polar residues (glutamine) also show hydration effects, though less pronounced than charged residues.

    Conclusions:

    • The location of polar residues is critical when using copolymers to study helix-forming tendencies.
    • Random copolymers utilizing a neutral, water-soluble host provide reliable data for amino acid helix propensities.
    • This approach allows for accurate assessment of 'guest' amino acid helix-forming abilities within a well-defined 'host' sequence.