Fig. 6.

The DNase IPE is an extended loop that adopts a conserved structure.

(A) Cartoon representation of the DNase domain of AP41 with C^α traces of the DNase IPE for ColE2, ColE7, ColE9, PyoS2 and PyoAP41 in complex with their cognate Im—data not shown here. The IPE does not adopt any regular secondary structure but the different sequences superpose well (0.56 Å RMSD for backbone atoms). (B) Cartoon representation of pyocin AP41 DNase domain (blue) with selected side chains shown as sticks and transparent space-filling spheres. Conserved amino acids in the IPE stabilise Pro721 that bridges the hydrophobic core of the enzyme (Trp694) to the Im binding site. In all DNase–Im complex structures, the residue following Pro721 makes contacts with the Im hotspot aromatic residues.