Mechanism of ATP dependence of MreB function. Glu140^Cc (CcMreB numbering) plays a pivotal role in ATP-dependent conformational change of MreB. Schematic (box): Glu140^Cc in the double-protofilament AMP-PNP–bound state (PDB accession no. 4CZJ) holds the IB and IIA subdomain via water-mediated interactions, (a) and (b). These water-mediated interactions are not present for ADP single filament (PDB accession no. 4CZF) and AMP-PNP monomeric state (PDB accession no. 4CZM), where Glu140^Cc functions only in Mg²⁺ coordination.