Helix-coil transition theories. Are they correct?

Area of Science:

• Biochemistry
• Protein Folding
• Theoretical Chemistry

Background:

• Contemporary theories describe alpha-helix formation in polypeptide chains.
• These models often simplify the unfolded peptide state as a
• random coil
• which is not entirely realistic.
• This simplification may affect the accuracy of helix propagation parameters.

Purpose of the Study:

• Critically discuss current theoretical descriptions of alpha-helix formation.
• Investigate the factors influencing helix propagation and nucleation parameters.
• Propose an alternative explanation for the stability of short helical segments.

Main Methods:

• Analysis of theoretical models for alpha-helix formation.
• Evaluation of helix propagation parameters derived from model peptides.
• Postulation of the "helix end separation effect" based on residue solvation.

Main Results:

• Helix propagation parameters vary due to unrealistic "random coil" assumptions.
• The "nucleation parameter" is primarily determined by terminal residue solvation, not nucleation.
• Hydrophobic terminal residues can lead to unstable helical segments.
• A "helix end separation effect" enhances the stability of short helices.

Conclusions:

• Existing theories on alpha-helix formation require refinement.
• Solvation of terminal residues significantly impacts helix stability and nucleation.
• The "helix end separation effect" offers a new perspective on helix initiation.
• Further research is needed to validate these findings in diverse peptide systems.