Figure 7.

Schematic summarizing the proposed three-state unfolding model for DsbB in a dark nanodisc composed of DMPC/DMPG lipids. (A) DsbB reconstituted in a dark nanodisc loaded with DMPC/DMPG lipids under nonreducing conditions (i.e., the interloop C41–C130 disulfide bond is oxidized) as it thermally unfolds from the native state (N) to an intermediate state (I) and to the unfolded (U) state. We propose that the three-state/biphasic model is the result of a disulfide bond-mediated I state in the presence of DMPC/DMPG lipids. (B) DsbB reconstituted in a dark nanodisc under reducing conditions (i.e., the interloop C41–C130 disulfide bond is reduced) as it thermally unfolds from the N state to the U state. We do not observe the formation of an I state during thermal unfolding of DsbB in our dark nanodisc system under reducing conditions. DsbB is shown in dark gray, the dark nanodisc system is shown in light gray, the tryptophan and tyrosine content for DsbB is represented in purple, the loss in secondary structural content is reflected by gray ribbons in the U state, and the C41–C130 interloop disulfide bond in the oxidized state (left) or reduced state (right) is shown in yellow.