The thermo-responsive regulation of Yersinia pestis immune protective protein (F1) by the Caf1R transcription factor

Abstract

Pathogenic bacteria can sense the temperature of the host body to provoke the production of required virulence factors that allow them to defend themselves from the host immune system. The molecular mechanism of such temperature-sensitive regulation might be at the transcriptional or translational level involving DNA, RNA or protein. In one example, when Yersinia pestis, (the plague causative bacterium) infects the flea where the temperature ≈ 25oC it does not produce the Capsular Antigen F1 (Caf1). However, the bacterium can sense the change in temperature when it invades the human body and produces the Caf1 polymer as a coat to avoid the phagocytosis. The gene transcription of the caf1 operon is increased in response to body temperature (37oC). Although Caf1R is thought to be the responsible factor for such transcriptional upregulation, there are no clear results explaining the mode of action of Caf1R. In this study it was shown that caf1R gene deletion stops the secretion of Caf1 polymer. Caf1R is the transcription factor responsible for the immediate thermal upregulation of caf1 operon genes. Using molecular biology techniques, it was found that the caf1 operon genes caf1M, caf1A and caf1 are transcribed as a single long mRNA. The deletion of one of three predicted promoter regions upstream of this region (between caf1R and caf1M) was seen to have a significant effect on the transcription of caf1 operon genes and protein production. Finally, Caf1R was exploited to generate a novel thermal responsive expression system, which can be induced by switching the temperature from 25oC to 35oC instead of using a chemical inducer like IPTG or L-arabinose. Although this expression system needs more development to be usable in biotechnology applications, gfp expression from this system was shown to be highly temperature dependent.