A homology model for hexameric R. capsulatus PBGS. A) The R. capsulatus PBGS detached dimer model, shown in stereo view, looking down the αβ-barrel domain of subunit A (red), directly into the active site. The two active site lysine residues, implicated in covalent catalysis , are shown ball-and-stick. The N and C termini are labeled for subunits B and A respectively. B) The hexamer is composed of three detached dimers, which are shown as ribbon representations and colored shades of red, blue, and green. For the dimer view only, side chains in regions where the model must accommodate deletions and/or insertions are shown as sticks colored as the subunit; amino acids homologous to, but different from those at the hugging dimer interface of P. aeruginosa PBGS are shown in space fill representation. In this representation, the N and C termini are visible for subunits A and B and are labeled in the dimer representation.