Structure of the CO sensing transcription activator CooA

CooA is a homodimeric transcription factor that belongs to the catabolite a ctivator protein (CAP) family. Binding of CO to the heme groups of CooA lea ds to the transcription of genes involved in CO oxidation in Rhodospirillum rubrum, The 2.6 Angstrom structure of reduced (Fe2+) CooA reveals that His 77 in both subunits provides one heme ligand while the N-terminal nitrogen of Pro 2 from the opposite subunit provides the other ligand. A structural comparison of CooA in the absence of effector and DNA (off state) with tha t of CAP in the effector and DNA bound state (on state) leads to a plausibl e model for the mechanism of allosteric control in this class of proteins a s well as the CO dependent activation of CooA.