Fig. 2.

The EcUppP substrate-binding pocket. a Clipped view of the EcUppP substrate-binding pocket from a periplasmic viewpoint showing the electronegative funnel and deep hydrophobic channel leading into the positively charge basin formed by the antiparallel inverted reentrant helices defining the active site. An observed monoolein lipid is shown in stick with the polar headgroup bound in the active site pocket and lipid tail exiting the cleft along the hydrophobic channel. b Magnified view of the EcUppP active site with key catalytic residues shown in stick. Two modeled active site waters are shown as cyan and green spheres representing the proposed catalytic water and a putative cation-binding site, respectively. c His30 forms structural hydrogen bonds with the backbones amides of Val25 and Ser26, as well as the hydroxyl oxygen of Tyr260. d Arg261 is buried at the membrane midplane (also see Supplementary Fig. 6) and forms a hydrogen-bonding network that links both reentrant loops (RE Loop 1/2) through the backbone amides of Pro24, Gly171, and F172, in addition to α5 through the backbone amide of Leu126