Allosteric movements in eubacterial RecA.

The action of RecA, an important eubacterial protein involved in recombination and repair, involves the transition from an inactive filament in the absence of DNA to an active filament formed in association with DNA and ATP. The structure of the inactive filament was first established in Escherichia coli RecA (EcRecA). The interaction of RecA with non-hydrolysable ATP analogues and ADP has been thoroughly characterized and the DNA binding loops visualized based on the crystal structures of the RecA proteins from Mycobacterium tuberculosis (MtRecA) and Mycobacterium smegmatis (MsRecA). A switch residue, which triggers the transformation of the information on ATP binding to the DNA binding regions, has been identified. The 20-residue C-terminal stretch of RecA, which is disordered in all other relevant crystal structures, has been defined in an MsRecA-dATP complex. The ordering of the stretch is accompanied by the generation of a new nucleotide binding site which can communicate with the original nucleotide binding site of an adjacent molecule in the filament. The plasticity of MsRecA and its mutants involving the switch residue has been explored by studying crystals grown under different conditions at two different temperatures and, in one instance, at low humidity. The structures of these crystals and those of EcRecA and Deinococcus radiodurans RecA (DrRecA) provide information on correlated movements involving different regions of the molecule. These correlated movements appear to be important in the allosteric transitions of RecA during its action.