a, The isolated WztN dimer structure was aligned by secondary matching in Coot with the NBDs of the adenosine 5′-(β,γ-imido)triphosphate-stabilized maltose transporter (Protein Data Bank accession number 3RLF). The WztN dimer is shown in cyan and light blue, and the NBDs of the maltose transporter are shown in light and dark grey. Right: the Walker A (S61) and signature (S143) motifs in the closed WztN dimer structure are separated by approximately 4 Å. b, Comparison of WztN dimer structures. The structure shown in dark blue was obtained from a crystal form containing a WztN dimer in the crystallographic asymmetric unit. The structure shown in grey was obtained from a crystal form with a monomeric WztN per crystallographic asymmetric unit related to the other protomer by two-fold crystallographic symmetry. The signature motifs are coloured cyan and yellow, and the Walker A motifs are coloured magenta and red for the crystallographic monomeric and dimeric WztN structures, respectively.