A designed system for assessing how sequence affects alpha to beta conformational transitions in proteins.

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• The role of amino acid sequence in protein conformational switching, particularly in prions and amyloid diseases, remains unclear.
• Understanding alpha-helical to beta-sheet transitions is crucial for deciphering protein misfolding disorders.

Purpose of the Study:

• To investigate how specific amino acid sequences influence conformational transitions from alpha-helices to beta-sheets.
• To design peptides with dual structural characteristics (alpha-helical leucine zipper and beta-hairpin) to study this transition.

Main Methods:

• Designed peptides with features of both leucine zippers and beta-hairpins.
• Utilized circular dichroism spectroscopy and analytical ultracentrifugation to characterize peptide structures.
• Induced conformational changes through heat and cross-linking.

Main Results:

• A modified peptide (Template-alphaT) with threonine substitutions exhibited a heat-inducible switch to beta-structure, forming amyloid-like fibrils.
• Destabilization of the leucine-zipper form did not induce amyloid formation, unlike in some natural proteins.
• Cross-linking peptide termini compatible with beta-hairpin structure promoted the transition.

Conclusions:

• Specific residue placements favoring beta-structure are critical for promoting amyloid formation.
• Conformational switching is influenced by sequence-specific interactions beyond general polypeptide backbone properties.
• Peptide design can control transitions between alpha-helical and beta-sheet structures, leading to amyloid formation.