CRYSTAL-STRUCTURE OF AMIC - THE CONTROLLER OF TRANSCRIPTION ANTITERMINATION IN THE AMIDASE OPERON OF PSEUDOMONAS-AERUGINOSA

The crystal structure for the negative regulator (AmiC) of the amidase operon from Pseudomonas aeruginosa has been solved at a resolution of 2.1 Angstrom AmiC is the amide sensor protein in the amidase operon a nd regulates the activity of the transcription antitermination factor AmiR, which in turn regulates amidase expression. The AmiC structure c onsists of two domains with an alternating beta-alpha-beta topology. T he two domains are separated by a central cleft and the amide binding site is positioned in this cleft at the interface of the domains. The overall fold for AmiC is extremely similar to that for the leucine-iso leucine-valine binding protein (LivJ) of Escherichia coli despite only 17% sequence identity, however, the two domains of AmiC are substanti ally closed compared with LivJ. The closed structure of AmiC is stabil ized significantly by the bound acetamide, suggesting a molecular mech anism for the process of amide induction. The amide binding site is ex tremely specific for acetamide and would not allow a closed conformati on in the presence of the anti-inducer molecule butyramide.