Crystal structure of the SPOR-RlpA domain and PG binding. a The ribbon structure is displayed in two orientations at 90° of each other, with the assigned secondary structure elements depicted. b The electrostatic potential of the surface of the domain is shown in the SPOR:1 complex. Compound 1 is represented as capped sticks colored by atom types (carbons in green, oxygens in red and nitrogens in blue). The color key shows the Poisson-Boltzmann electrostatic-potential surface (color bar range ± 53.05 kT/e). c The details of the recognition of denuded PG by the SPOR domain are shown, with the residues involved in PG recognition labeled and those contributing only through main-chain interactions given a number. Relevant residues and crystallographic water molecules are shown as capped sticks and spheres, respectively. Polar interactions are represented as dotted lines.