The overall structure of EcppnP shows RmlC-like cupins fold
The recombinant native Ec ppnP protein was crystallized in space group P 62 diffracted to 1.38 Å resolution, and the initial phase was determined by the single-wavelength anomalous dispersion (SAD) method using selenomethionine-labeled crystal, which is also diffracted to 1.38 Å resolution belongs to the same space group (Table 1 ). The final R work and R freevalues of the high-resolution structure are 0.1522 and 0.1780, respectively (Table 1 ). The electron density is continuous for the full-length protein; thus, we can model the full-lengthEc ppnP structure. There is one Ec ppnP molecule in the asymmetric unit and the overall structure of Ec ppnP contains eleven beta-strands composing a dual-layer β-fence (Figure 1A ). The β1-β2-β3-β10-β5-β8 compose an antiparallel β-sheet and the other side contains an antiparallel β4-β9-β6-β7 sheet (Figure 1A, B ). Therefore, the structure of Ec ppnP we solved belongs to the cupin fold superfamily, which is among the most functionally diverse superfamily and comprises both enzymatic and non-enzymatic members containing either one or two cupin domains 13. Within the conserved tertiary structure, the variety of biochemical functions is provided by minor variation of the residues in the active site and the identity of the bound metal ion 14.