Fig. 5: The structure of CroT.

a, Ribbon representation of a selected CroT enzyme in the crystal structure of Bcs3-CMP. The orientation displays the catalytic face view revealing the overall architecture and the active site location. The following two Rossmann-folded domains are colored: CroT-NT (pale orange, residues 1–161 and 352–373) and CroT-CT (gray, residues 162–351). The catalytic site cleft is indicated with a dashed box. Note the position of the CMP and glycerol in the cleft and the surrounding loops forming the active site as follows: loop 1 (red, residues 195–205, connecting β7-α11), loop 2 (light blue, residues 231–233, connecting β8-α13), loop 3 (orange, residues 277–279, connecting β10-α16) and loop 4 (pink, residues 94–103, connecting β5-α4). b, Corresponding surface representation highlights how the closed conformation adopted by CroT buries CMP. c, Coulombic charge surface representation. Note that the entrance to the catalytic site shows a general positive charge distribution. d, Detail of the active site in ribbons showing the docked CDP-ribitol, a phosphate and active site residues. H96 and the side chains of H233 and K101 accommodate the pyrophosphate moiety. e,f, Ribitol is accommodated in a deep cavity formed by loop 4, which complements the charge distribution of the ligand. g, A zoomed-out view shows the NT-domain groove, which might function as a putative entrance for the acceptor substrate (nonreducing end ribose). The phosphate found in the groove indicates a potential polymer-binding site. Note that the β-phosphate of CDP-ribitol is oriented toward the putative active site entrance.