Probing the influence of sequence-dependent interactions upon alpha-helix stability in alanine-based linear peptides

Area of Science:

• Biochemistry
• Computational Chemistry
• Protein Structure

Background:

• Short, linear alanine-based polypeptides readily form stable alpha-helices in aqueous solution.
• This system allows detailed study of how amino acid sequences affect secondary structure stability.

Purpose of the Study:

• To rationalize observed variations in alpha-helical stability using computational methods.
• To investigate the role of side-chain-backbone and side-chain-side-chain interactions in peptide secondary structure.

Main Methods:

• Detailed conformational searches were performed on six alanine-based peptides.
• A simple, gas-phase potential model was employed to calculate conformational energies.
• Results were compared with experimental data on relative alpha-helical stabilities.

Main Results:

• Calculations using a gas-phase model accurately predicted relative alpha-helical stabilities.
• Valine, isoleucine, and phenylalanine residues were found to destabilize alpha-helices.
• Destabilization is linked to unfavorable side-chain-backbone interactions, promoting 3(10)-helix formation, particularly with valine due to entropic effects.
• Very short-range interactions may explain nucleation and propagation parameters in helix-coil theories.

Conclusions:

• Computational modeling provides insights into amino acid sequence effects on peptide secondary structure.
• Specific residues like valine, isoleucine, and phenylalanine can disrupt alpha-helix formation.
• Findings align with and complement existing theories of helix-coil transitions and molecular dynamics simulations.