Transitioning into the Ripped states.

<p>A. The initial structure in a space-filling representation prior to pulling, with the β1 (green) strand nestled between the darker colored β6 (blue) and β2 (red) strands. The N-terminal α-helix is colored to illustrate the N-terminal deletions (yellow (Δ5) and orange (Δ8)). B. A partially unpeeled β1 strand leaving behind a gap between strands β6 and β2 through which the chromophore (green) can be seen. C. A completely extracted β1 strand with the β6 and β2 strands resealed. D. The initial configuration in the ribbon representation with the β1 strand colored in green. The amino acid residues that form new contacts are shown in the space filling representation. E. The resealed barrel. F. The distances between the atoms involved in hydrogen bond formation from the pull at 200 pN that best demonstrated resealing behavior. Contacts between Gly31-Asn121 as well as Gly33-Leu119 are more stable than the contacts between Val29-Ile123. G. The one case where the barrel did not reseal. However, there is a remaining stable “mechanical core” shown in red that bears a structural resemblance to an intermediate state of the first type III module from human fibronectin <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046962#pone.0046962-Gao1" target="_blank">[38]</a>. H. The first human fibronectin type III module (FnIII-1) in the intermediate state <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046962#pone.0046962-Gao1" target="_blank">[38]</a>.