A Designed System for Assessing How Sequence Affects α to β Conformational Transitions in Proteins*

By Barbara Ciani, E. Hutchinson, R. Sessions, Derek N. Woolfson. Journal of Biological Chemistry, 2002

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The role of amino acid sequence in conformational switching observed in prions and proteins associated with amyloid diseases is not well understood. To study α to β conformational transitions, we designed a series of peptides with structural duality; namely, peptides with sequence features of both an α−helical leucine zipper and a β−hairpin. The parent peptide, Template−α, was designed to be a canonical leucine-zipper motif and was confirmed as such using circular dichroism spectroscopy and analytical ultracentrifugation. To introduce β−structure character into the peptide, glutamine residues at sites away from the leucine-zipper dimer interface were replaced by threonine to give Template−αT. Unlike the parent peptide, Template−αT underwent a heat-inducible switch to β−structure, which reversibly formed gels containing amyloid-like fibrils. In contrast to certain other natural proteins where destabilization of the native states facilitate transitions to amyloid, destabilization of the leucine-zipper form of Template−αT did not promote a transformation. Cross-linking the termini of the peptides compatible with the alternative β−hairpin design, however, did promote the change. Furthermore, despite screening various conditions, only the internally cross-linked form of the parent, Template−α, peptide formed amyloid-like fibrils. These findings demonstrate that, in addition to general properties of the polypeptide backbone, specific residue placements that favor β−structure promote amyloid formation.

Subfields: Computational Theory and Mathematics, Molecular Biology

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