Structure of the Escherichia coli FlhDC complex, a prokaryotic heteromeric regulator of transcription

The hetero-oligomeric complex of the FlhD and FlhC proteins (FlhDC) regulates transcription from several flagellar and non-flagellar operons in bacteria. The crystallographic structure of the Escherichia coli FlhDC complex has been solved to 3.0 angstrom resolution, revealing a hexameric FlhD(4)FlhC(2) assembly. In the complex, each FlhC protomer binds an FlhD(2) dimer; the conformation of the dimer in the complex differs significantly from its conformation in the absence of FlhC. FlhC has a novel tertiary fold that includes a heretofore unrecognized zinc-binding site in which the ion is ligated by four cysteine residues. Gel shift experiments show that binding of the FlhDC complex to a cognate promoter bends the DNA by approximately 111 degrees. The structure of the FlhDC complex is compatible with models in which a fragment of operator DNA, at least 48 base-pairs in length, wraps around the complex and bends significantly when binding. (c) 2005 Elsevier Ltd. All rights reserved.