1A-03 Functional replacement of the AAA+ sensor 1 motif in DnaA, the initiator of chromosomal replication in E.coli

Escherichia coli DnaA protein, a member of the AAA+ superfamily, initiates chromosomal replication in an ATP-binding-dependent manner. Although DnaA has conserved Walker A/B motifs, it binds adenine nucleotides 10-100-fold more tightly than do many other AAA+ proteins. We found that an Asp residue, located in the sensor 1 motif, plays a specific role in supporting high affinity ATP/ADP binding. Whereas the acidic Asp residue is highly conserved among eubacterial DnaA homologs, the corresponding residue in many other AAA+ proteins is Asn/Thr and in some AAA+ proteins these neutral residues are essential for ATP hydrolysis but not ATP binding. As the intrinsic ATPase activity of DnaA is extremely weak, this study reveals a novel and specific function for the sensor 1 motif in tight ATP/ADP binding, one that depends on the alternate key residue Asp.