Fig. 1. Structure of the AAA module based on the crystal structure data of HslU from Bochtler et al. (1999). The N-terminal α–β–α nucleotide subdomain is in cyan (α helices) and yellow (β sheet), and the C-terminal helical domain is in blue. ADP (green and magenta) binds between the subdomains, with the Walker motif residues Lys63 (blue) and Asp256 (red) and the Sensor 1 residue Ser307 nearby.