The VirS-VirR two component system in Closridium perfringens

Robyn Adams, Omar Barifah and Angela Burbage

School of Life Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, UK.

Most living organisms, including almost all prokaryotes and some lower eukaryotes such as yeast, have evolved

their ability to sense and adapt the changes in their external environment in order for nutrients, survival and

proliferation [2]. The two-component system plays a significant role in the physiology of such organisms. It consists

of a senor histidine kinase, which is a transmembrane bound protein, as well as its associated response-regulator,

which is a cytoplasmic protein regulator that regulates target gene expression [2]. The Gram-positive anaerobe

Clostridium perfringens is known to produce a wide variety of different extracellular toxins and enzymes due to

alternation of target gene expression via the VirS-VirR two-component system [2].

The transmembrane bound VirS which is stimulated by its

surroundings, is auto-phosphorylated at the N-terminal domain

which contains a histidine residue (His255) [1]. The VirS acts as

a donor by phosphorylating an Aspartate-57 residue on the N-

terminal domain of its associated cytoplasmic response regulator

VirR [2], the VirR regulator acts as a regulon as illustrated in

Fig.1 [5]. The phosphorylated VirR-P directly triggers the

transcription of both genes pfoA and vrr. The vrr gene directly

transcribes an RNA molecule which acts as a regulatory

compound (VR-RNA) and consequently the VR-RNA molecule

transcribes additional genes such as plc and colA which are

involved in toxin production (Fig.1) [2].

The external environmental stimulus is still not known however;

it has been hypothesized that the detection of the environmental

stimuli is attributable to the high variability of the extracellular N-

terminal domain on the sensor histidine kinase, which enables

the detection of external environmental signals [2]. When

activated, this causes a cellular response, which activates target

gene expression to produce extracellular toxins such as alpha-

toxin (phospholipase C) and theta-toxin (perfringolysin O), as

well as enzymes such as sialidase and protease. The toxins and

enzymes released will degrade cells where the contents is

released, enabling C.perfringens to acquire nutrients [3] causing

gas gangrene and myonecrosis [1].

1. Cheung, J. K. and Rood, J. I. (2000) 'The VirR response regulator from Clostridium perfringens binds independently to two imperfect direct repeats located upstream

of the pfoA promoter', Journal of Bacteriology, 182(1), 57-66.

2. Cheung, J. K. and Rood, J. I. (2006) 'Two-component signal transduction systems: the adapt and survive response', Microbiology Australia, 27(3), 101-104.

3. Ohtani K , Hirakawa H, Tashiro K, Yoshizawa S, Kuhara S, Shimizu T (2010) Identification of a two component VirR/VirS regulon in Clostridium perfringens

Anaerobe 16,258–264

4. Okumura K, Ohtani K, Hayashi H, and Tohru Shimizu T, (2008) Characterization of Genes Regulated Directly by the VirR/VirS

System in Clostridium perfringens Journal of Bacteriology 190, 7719-7727

Figure 1. Shows the mechanism in the VisS-VirR two component system for Clostridium perfringens [2].

Research by Cheung and Rood (2000) examined the transcription activity between VirR and three genes plc, colA

and pfoA. The study showed that VirR directly binds upstream only to the promoter region of the gene pfoA

because evidence shows in the absence of VirR, transcription of pfoA is inhibited and therefore there is no

production of the toxin perfringolysin O (Fig.1) [1]. Additionally the research also showed that there was no similar

binding site for genes pfoA, plc and colA therefore implying there is another regulatory gene involved in

transcription of genes plc and colA [1]. Okumura et al (2008) showed that the regulatory gene is called vrr gene

which encodes a regulated RNA molecule that expresses additional genes such as housekeeping genes,

virulence-related genes, genes involved in quorum sensing and the genes coding alpha-toxin (phospholipase C)

and kappa-toxin (collagenase) (Fig.2) [2,4]. Thus, the VirR is involved both directly and indirectly in the production

of toxins [2].

Figure 2. Schematic diagram of the VirR/VirS regulon [4].

Introduction

Components of system

Environmental signal and cellular response

The role of the two components systems in the control mechanism

References