The structure of Mg-ATPase nucleotide-binding domain at 1.6 Å resolution reveals a unique ATP-binding motif

The structure of the nucleotide‐binding domain of the Mg‐ATPase MgtA from Escherichia coli has been solved and refined to 1.6 Å resolution. The structure is made up of a six‐stranded β‐sheet and a bundle of three α‐helices, with the nucleotide‐binding site sandwiched in between. The MgtA nucleotide‐binding domain is shorter and more compact compared with that of the related Ca‐ATPase and lacks one of the β‐strands at the edge of the β‐sheet. The ATP‐binding pocket is surrounded by three sequence and structural motifs known from other P‐type ATPases and a fourth unique motif that is found only in Mg‐ATPases. This motif consists of a short polypeptide stretch running very close to the ATP‐binding site, while in Ca‐ATPase the binding site is more open, with the corresponding polypeptide segment folded away from the active site.