(a) Structure comparison between BcPPNE (left) and CPNE BcYkfC (right, PDB 3h41). The N-terminal subdomains of both proteins are colored grey, and the C-terminal subdomains in violet. The catalytic residues are shown as ball-and-sticks. The sites of the circular permutation are indicated by residue numbers. (b) Core conserved secondary structures within the NlpC/P60 superfamily. Cα traces for the conserved cores of BcPPNE (green), YiiX (cyan), BcYkfC (yellow), PPPDE1 (magenta) the conserved residues are superposed. Secondary structures of BcPPNE (green) and catalytic residues of YiiX (sticks) are highlighted. (c) Sequence alignment between PPNEs (BcPPNE, YiiX, human PPPDE1, vaccinia virus G6R, human LRAT), and CPNE BcYkfC. Sequence numbering and secondary structures of BcPPNE are shown at the top. The 310 helices are shown in red and other secondary structures are labeled as in Fig. 1. Sequences of the two subdomains of BcYkfC are swapped in comparison to the others and the respective residue ranges are shown near the ends of the permuted segments.