For featurizations that combine inverse distances d -1 with backbone dihedrals (ϕ, ψ), eight of the nine force fields had VAMP-2 scores that were statistically indistinguishable from featurizations of inverse distances alone. For this reason, we selected inverse distance d -1 features alone to construct all subsequent Markov models. The one statistically significant Rare 2:2 turn formation produces large VAMP-2 scores for AMBER14SB. To understand the importance of dihedral angles to featurizing the AMBER14SB trajectory data, we built complete models for AMBER14SB using this featurization (Figure ). The inclusion of dihedral angles lead to a new distribution in tICA, with a low density of samples separated from the rest along independent components IC1 and IC2 (Figure ). In addition to producing higher featurization VAMP-2 scores (see Figure ), inclusion of dihedral angles leads to higher average MSM VAMP-2 scores for microstate MSMs (Figure ), and a large increase (up to ∼10 µs) in the slowest implied timescale (Figure ). These 10 findings suggested that backbone (ϕ,ψ) dihedral featurization captures a rare slow protein motion that could impact MSM coarse-graining. To further investigate the source of this slow motion, we examined a specific trajectory that visits the low-density region (Figure ). Distinct Glu5-ϕ and Pro4-ψ dihedral angles sampled in the low-density region reveals the formation of a unique 2:2 turn, with Glu5 sampling a left-handed α-helical conformation (Figure ).