L. Pearl et al., CRYSTAL-STRUCTURE OF AMIC - THE CONTROLLER OF TRANSCRIPTION ANTITERMINATION IN THE AMIDASE OPERON OF PSEUDOMONAS-AERUGINOSA, EMBO journal, 13(24), 1994, pp. 5810-5817
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.