ArgP protein of Escherichia coli: roles in osmoregulation, gene regulation and inter-relationship with LysG of Corynebacterium glutamicum

Abstract

The ArgP protein of Escherichia coli had previously been described variously by different investigators as an inhibitor of oriC-initiated DNA replication, a nucleoid-associated protein and as a transcriptional regulator of genes involved in DNA replication (dnaA, nrdA), osmoregulation and amino acid metabolism (argO, dapB, gdhA and#61531;the last in Klebsiella pneumoniaeand#61533;). In the studies reported in this thesis, promoter-lac fusions were examined in argP+, and#61508;argP and dominant argP (argPd) mutations bearing strains to identify additional ArgP-regulated genes. The genes gdhA, lysP, lysC, lysA, dapD, and asd were newly identified as ArgP-regulated. All were repressed upon Lysine (Lys) supplementation, and in vitro studies demonstrated that ArgP binds to the regulatory regions in a Lys-sensitive manner ( in contrast to the behaviour at argO, where ArgP binding is Lys-insensitive). Unlike previous reports, neither dnaA nor nrdA was ArgP-regulated in vivo, although their regulatory regions did exhibit non-canonical low-affinity binding to ArgP in vitro. ArgP-argO of E. coli and LysG-lysE of Corynebacterium glutamicum are orthologous regulator-target gene pairs. While LysE is an exporter of both arginine (Arg) and Lys whose expression is induced by Arg, Lys, or histidine (His), ArgO exports Arg alone and its expression is activated by Arg but not Lys or His. In studies reported in this thesis, reconstitution of LysG activation of lysE in E. coli was achieved. Neither ArgP nor LysG could regulate expression of the non-cognate targets, but the ArgPd variants -P274S, -S94L -P108S activated lysE expression in E. coli. The activating effects of LysG and ArgPd on lysE were mutually extinguished when both proteins were co-expressed in Arg- or His-supplemented cultures. Compared to native ArgP, these ArgPds exhibited higher affinity of binding to lysE and less DNA bending at both argO and lysE.