Polymorphism of Collagen Triple Helix Revealed by super(19)F NMR of Model Peptide [Pro-4(R)-Hydroxyprolyl-Gly] sub(3)-[Pro-4(R)-Fluo roprolyl-Gly]-[Pro-4(R)-Hydroxyprolyl-Gly] sub(3)

We have characterized various structures of (Pro-Hyp super(R)-Gly) sub(3)-P ro-fPro super(R)-Gly-(Pro-Hyp super(R)-Gly) sub(3) in the process of cis-trans isomerization and helix-coil transition by exploiting the sole super(19)F NMR probe in 4(R)-fluoroproline (fPro super(R)). Around the transition temperature (T sub(m)), we detected a species with a triple helical structure distinct from the ordinary one concerning the alignment of three strands. The super(19)F- super(19) F exchange spectroscopy showed that this misaligned and that the ordinary triple helices were interchangeable only indirectly via an extended monomer strand with all-trans peptide bonds at Pro-fPro super(R), Pro-Hyp super(R), and Gly-Pro in the central segment. This finding demonstrates that the helix-coil transition of collagen peptides is not described with a simple two-state model. We thus elaborated a scheme for the transition mechanism of (Pro-Hyp super(R)-Gly) sub(n) that the most extended monomer strand can be the sole source both to the misaligned and correctly folded triple-helices. The staggered ends could help misaligned triple helices to self-assemble to higher-order structures. We have also discussed the possible relationship between the misaligned triple helix accumulating maximally at T sub(m) and the kinetic hysteresis associated with the helix-coil transition of collagen.