Structural adaptation of an interacting non-native C-terminal helical extension revealed in the crystal structure of NAD⁺ synthetase from Bacillus anthracis

The C-terminal His tag is resolved in the structures of the apoenzyme and complexes with AMP and pyrophosphate or a substrate analog of ATP, wherein it is found to interact with native residues at the dimer interface. In the complex structures, it partially occupies the native binding site for the substrate NaAD.