Modulation of QscR, a quorum sensing receptor of Pseudomonas aeruginosa, by truncation of a signal binding domain

Abstract

In Pseudomonas aeruginosa, a multi-host pathogen, quorum sensing (QS) plays an essential role in pathogenesis, wherein LasR, QscR and MAR, the QS regulators, control the expression of many virulence factors. In this study, we constructed a signal-binding-domain (SBD)-deleted QscR (QscR(160-237)) to make a signal-independently-active form of QscR. However, QscR(160-237) that has only a DNA binding domain (DBD) was not fully active. It was able to bind to the target site in a signal-independent manner, but was not able to activate transcription of the target promoter. Since QscR(160-237) could interfere with binding of wild-type QscR (QscR(wt)) to its QscR binding site, we investigated the competition between QscR(160-237) and QscR(wt) on the QscR binding site in vivo and in vitro. When QscR(wt) and QscR(160-237) were independently co-expressed by two different inducers, increasing expression of QscR(160-237) interfered with QscR(wt) activity. This was verified by a competitive gel shift assay in vitro using purified QscR(wt) and OscR(160-237). Our results show that the SBD deletion makes QscR a partially active form that has only DNA binding ability, but it can interfere with QscR(wt) by competitive binding.