The cover illustrates a model of the gp130 FN III domain 5 with the C-C' loop shown in 2 orientations (green and mauve). It is predicted that this 8-residue loop, tethered by the disulfide bond Cys436--Cys444, maintains Cys469 in a reduced form available for ligand-induced intramolecular disulfide bond formation. Details can found in the article by Moritz et al., pages 8244--8253..