  The interconversion between left- and right-handed helical folds of a
polypeptide defines a dual-funneled free energy landscape. In this context, the
funnel minima are connected through a continuum of unfolded conformations,
evocative of the classical helix-coil transition. Physical intuition and recent
conjectures suggest that this landscape can be mapped by assigning a left- or
right-handed helical state to each residue. We explore this possibility using
all-atom replica exchange molecular dynamics and an Ising-like model,
demonstrating that the energy landscape architecture is at odds with a
two-state picture. A three-state model - left, right, and unstructured - can
account for most key intermediates during chiral interconversion. Competing
folds and excited conformational states still impose limitations on the scope
of this approach. However, the improvement is stark: Moving from a two-state to
a three-state model decreases the fit error from 1.6 $k_B T$ to 0.3 $k_B T$
along the left-to-right interconversion pathway.
