Type I periplasmic components of amide-binding protein (AmiC) and the active transport system for short-chain and urea (FmdDEF)
This group includes the type I periplasmic components of amide-binding protein (AmiC) and the active transport system for short-chain and urea (FmdDEF), found in bacteria and Archaea. AmiC controls expression of the amidase operon by a ligand-triggered conformational switch. In the absence of ligand or presence of butyramide (repressor), AmiC (the ligand sensor and negative regulator) adopts an open conformation and inhibits the transcription antitermination function of AmiR by direct protein-protein interaction. In the presence of inducing ligands such as acetamide, AmiC adopts a closed conformation which disrupts a silencing AmiC-AmiR complex and the expression of amidase and other genes of the operon is induced. FmdDEF is predicted to be an ATP-dependent transporter and closely resembles the periplasmic binding protein and the two transmembrane proteins present in various hydrophobic amino acid-binding transport systems.