DNA recognition by Escherichia coli CbpA protein requires a conserved arginine-minor-groove interaction

Curved DNA binding protein A (CbpA) is a cochaperone and nucleoid associated DNA binding protein conserved in most gamma-proteobacteria. Best studied in Escherichia coli, CbpA accumulates to > 2500 copies per cell during periods of starvation and forms aggregates with DNA. However, the molecular basis for DNA binding is unknown; CbpA lacks motifs found in other bacterial DNA binding proteins. Here, we have used a combination of genetics and biochemistry to elucidate the mechanism of DNA recognition by CbpA. We show that CbpA interacts with the DNA minor groove. This interaction requires a highly conserved arginine side chain. Substitution of this residue, R116, with alanine, specifically disrupts DNA binding by CbpA, and its homologues from other bacteria, whilst not affecting other CbpA activities. The intracellular distribution of CbpA alters dramatically when DNA binding is negated. Hence, we provide a direct link between DNA binding and the behaviour of CbpA in cells.