Spin Relaxation Enhancement Confirms Dominance of Extended Conformations in Short Alanine Peptides

摘要

Mounting spectroscopic evidence indicates the presence of local order in unfolded proteins, including polyproline II (PII). The data supporting this order rely on short-chain models, while the evidence for random-coil behavior is derived from measurements on a different length scale. Several theoretical papers have addressed this so-called "reconciliation problem", showing that excluded volume and local conformational preferences can account for the seemingly discrepant descriptions. We reexamine herein the dimensional properties of short Ala chains, which serve as general models for the protein backbone, using paramagnetic proton spin relaxation enhancement to evaluate the intramolecular intermediate-range distances (r).