CASTp 33 was used to investigate the pocket volume of ParcuCDPS and highlighted pocket residues which are unique. 21 P1 (shown in blue in Fig. ) is found deeper within the enzyme and is smaller and more restricted in size than P2 which sits at the solvent-accessible edge of the CDPS (red on Fig. ). The large size of P2 further explains poor positioning of Pro-DBE as the substrate can potentially sample several conformations, most of which are likely unproductive.