Atomic details of the native and derivative TollN6–VLR crystal structures. (a) Crystal of the N-terminal domain of the Toll receptor. The six LRRs are capped with disulfide-rich regions at the N- (LRRNT) and C-terminus (LRRCT). Toll is represented in cyan and VLR in grey. The fusion occurs at LRR6. (b) Building blocks of the crystal structures. Native and derivative crystals both contain head-to-head pairs of TollN6–VLR molecules interacting at their concave–convex interface. Upon superposition of the green molecules (light green from the native structure, dark green from the derivative one) it appears that the arrangement of the blue molecules is shifted by 40° to accommodate binding of the magic triangle I3C between the concave and the convex sides in the derivative structure. (c) Packing organization of the native structure. The native structure contains four molecules per asymmetric unit, with two pairs linked by a pseudo-twofold axis of symmetry. Top and side views are depicted. Glycan structures are represented as spheres coloured according to the Toll chain that they relate to. The VLR fusion is shown in grey. Malonate ions (in red or blue) are located at the right flank of the leucine-rich motif of the glycoprotein in its native state. (d) Higher-order symmetry of the derivative structure. Toll bound to I3C has a tetragonal symmetry, compared to the orthorhombic one of the native form. It only has two molecules per asymmetric unit. Two adjacent asymmetric units are shown to highlight the difference in crystal packing. The different views are given in the same orientation in (c)–(d) and asymmetric units have been boxed to show the differences between the crystal forms. (e)–(f) Binding modes of malonate in the native structure. (g) Binding of I3C in the derivative structure. I3C is represented in yellow at the concave side of Toll. The 2Fo−Fc map is shown in grey contoured at a level 3 and the difference map is shown in red at a level 5. Figure adapted from Gangloff et al. (2013).