X-ray data sets were collected in house using a Bruker AXS Platinum 135 CCD detector controlled with the Proteum software suite (Bruker AXS Inc.) The X-ray source was Cu Kα radiation from a Rigaku RU200 X-ray generator equipped with Montel optics and operated at 50 kV and 90 mA. The X-ray data sets were processed with SAINT and scaled with SADABS (Bruker AXS Inc.). Relevant X-ray data collection statistics are listed in Table 1 .
The structure of KdnA was determined via molecular replacement using the software package PHASER,11 (link) with the coordinates of QdtB serving as the search model.12 (link) 4-fold averaging and solvent flattening yielded an electron density map that allowed for essentially a complete tracing of the KdnA polypeptide chain. The model was subjected to alternate cycles of refinement with REFMAC13 (link) and manual model building with COOT.14 (link),15 (link) KdnB was also solved using PHASER with the search model being that of PDB entry 3RF7. The KdnB model was refined in a similar manner as that for KdnA. Model refinement statistics are listed inTable 2 .
The structure of KdnA was determined via molecular replacement using the software package PHASER,11 (link) with the coordinates of QdtB serving as the search model.12 (link) 4-fold averaging and solvent flattening yielded an electron density map that allowed for essentially a complete tracing of the KdnA polypeptide chain. The model was subjected to alternate cycles of refinement with REFMAC13 (link) and manual model building with COOT.14 (link),15 (link) KdnB was also solved using PHASER with the search model being that of PDB entry 3RF7. The KdnB model was refined in a similar manner as that for KdnA. Model refinement statistics are listed in
