The C-terminal substrate binding domain of LysR-type transcriptional regulator, ArgP (IciA), for arginine exporter (ArgO); contains the type 2 periplasmic binding fold.
The inhibitor of chromosomal replication (iciA) protein encoded by Mycobacterium tuberculosis, which is implicated in chromosome replication initiation in vitro, has been identified as arginine permease (ArgP), a LysR-type transcriptional regulator for arginine outward transport, based on the same amino sequence and similar DNA binding targets. Arp has been shown to regulate various targets including DnaA (replication), ArgO (arginine export), dapB (lysine biosynthesis), and gdhA (glutamate biosynthesis). With abundant nutrition, ArgP activates the DnaA gene (to increase replication) and the ArgO (to export redundant molecules). However, when nutrition supply is limited, it is suggested that ArgP might function as an inhibitor of chromosome replication in order to slow replication. This substrate-binding domain has significant homology to the type 2 periplasmic binding proteins (PBP2), which are responsible for the uptake of a variety of substrates such as phosphate, sulfate, polysaccharides, lysine/arginine/ornithine, and histidine. The PBP2 bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap. After binding their specific ligand with high affinity, they can interact with a cognate membrane transport complex comprised of two integral membrane domains and two cytoplasmically located ATPase domains. This interaction triggers the ligand translocation across the cytoplasmic membrane energized by ATP hydrolysis.