Work

Structure of a bacterial quorum-sensing transcription factor complexed with autoinducer-type pheromone and DNA

Year: 2002

Type: conference-abstract

Abstract: Some of the Escherichia coli cells produce plasmid-encoded toxic colicins that are secreted to kill closely related bacteria cells thereby they have better survival advantage during times of stress.The colicin E7 (ColE7) is one of the nuclease-type colicins, which contains a non-specific nuclease domain capable of hydrolyzing DNA in target cells.The nuclease activity of ColE7 is inhibited by the co-expressed immunity E7 protein (Im7), which binds to the nuclease domain of ColE7 in the host cell.The nuclease domain of ColE7 (nuclease-ColE7) contains a HNH motif, which has been identified in many endonucleases.The crystal structure of the phosphate-bound nuclease-ColE7/Im7 complex determined at 2.0 Å resolution with different metal ions showed that a phosphate ion was bound directly to the zinc ion in the HNH motif, suggesting that the zinc ion not only stabilizes the folding of the enzyme, but is also likely involved in DNA hydrolysis.Several residues located at positions close to the zinc-binding site were mutated to alanine and these mutants showed decreased or no nuclease activities.A gel retardation assay further demonstrated that the nuclease-ColE7 hydrolyzed DNA in the presence of zinc ions, but only bound to DNA in the absence of zinc ions.These results demonstrate that the zinc ion in the HNH motif of nuclease-ColE7 is not required for DNA binding, but is essential for DNA hydrolysis, suggesting that the zinc ion not only stabilizes the folding of the enzyme, but is also likely involved in DNA hydrolysis.

Source: Acta Crystallographica Section A Foundations of Crystallography

DOI: 10.1107/s0108767302095934