Exploring the mono-/bistability range of positively autoregulated signaling systems in the presence of competing transcription factor binding sites

Abstract

Binding of transcription factor (TF) proteins to regulatory DNA sites is key to accurate control of gene expression in response to environmental stimuli. Theoretical modeling of transcription regulation is often focused on a limited set of genes of interest, while binding of the TF to other genomic sites is seldom considered. The total number of TF binding sites (TFBSs) affects the availability of TF protein molecules and sequestration of a TF by TFBSs can promote bistability. For many signaling systems where a graded response is desirable for continuous control over the input range, biochemical parameters of the regulatory proteins need be tuned to avoid bistability. Here we analyze the mono-/bistable parameter range for positively autoregulated two-component systems (TCSs) in the presence of different numbers of competing TFBSs. TCS signaling, one of the major bacterial signaling strategies, couples signal perception with output responses via protein phosphorylation. For bistability, competition for TF proteins by TFBSs lowers the requirement for high fold change of the autoregulated transcription but demands high phosphorylation activities of TCS proteins. We show that bistability can be avoided with a low phosphorylation capacity of TCSs, a high TF affinity for the autoregulated promoter or a low fold change in signaling protein levels upon induction. These may represent general design rules for TCSs to ensure uniform graded responses. Examining the mono-/bistability parameter range allows qualitative prediction of steady-state responses, which are experimentally validated in the E. coli CusRS system.

Virulence regulation of Zn2+ uptake system znuABC on mesophilic Aeromonas salmonicida SRW-OG1

“…Although zinc is essential for organisms, excessive amounts of zinc can be harmful to cells ( 54 ). At physiological concentrations, zinc may have a protective effect against free radical formation ( 55 , 56 ), however, excess zinc has been shown to induce cytotoxicity by competing for protein binding with other metals ( 57 ), and exposure to high concentrations of zinc has been hypothesized to cause protein degeneration and dysfunction ( 58 ). There are mainly two Zinc transporters for zinc-uptake in most gram-negative bacteria, one is the znuABC , a high-affinity Zinc transport system, and the other is the low-affinity ZIP family Zn transporter ZupT ( 59 ).…”