Figure 5.
Ions captured in the MurJTA structure that might be involved in lipid II transport. (a) A chloride ion was observed in the first inward-facing (2.0-Å resolution, shown) and the inward-closed structures. Chloride was coordinated by Arg24, Tyr41, and Arg255, with the last being the only residue from the C-lobe and the rest from the N-lobe. Phe28, Phe42, and Phe184 are also in orientations suitable to form anion-quadrupole interactions with chloride. Anomalous difference electron density from a bromide soak is shown in brown mesh contoured to 4.5 σ. (b) A sodium ion was observed in the outward-facing (1.8-Å resolution, shown), inward-occluded, and inward-closed structures. Sodium was coordinated in trigonal bipyramidal geometry by Asn374, Asp378, Val390 (backbone carbonyl), Thr394, and Asp235, with the last being the only residue from the hinge helix TM7 (orange) and the rest from TM11/12. Omit electron density for sodium is shown in purple mesh contoured to 4.5 σ.
Abbreviations: MurJTA, Thermosipho africanus MurJ; TM, transmembrane helix.