Biophysical Journal 89 1

Cover picture: The interface and putative ammonia pathway between hisH and hisF: (A) Two conserved interdomain contacts in Thermotoga maritima are highlighted in space-filling: the cation-π pair (W123 of hisH in orange, R249 of hisF in blue) and the salt bridge between K181 of hisH (blue) and D98 of hisF (red). Conserved Y138, near the middle of the interface, demarks the exposed side of the interface from the intermolecular ammonia channel (shown in lavender spheres) that extends from the glutaminase active site histidine, H178, to the active site of hisF. (B) View of the entire ammonia channel, from the glutaminase active site to PRFAR. Conserved residues lining chamber I are depicted in gray surface representation, and the hisH active site histidine near the top of the chamber in licorice. Ammonia migrates into the hisF (β/α)8 barrel through a side opening near K99, chamber II, the constriction region, and the PRFAR cavity, where the PRFAR substrate (space-filling) is bound. Conserved residues are shown in licorice and the barrel strands in cartoon. This image was created with VMD. See the article by Amaro et al. on page 475.