A novel regulatory system promotes group A Streptococcus survival in human blood - PROJECT SUMMARY
The group A Streptococcus (GAS; S. pyogenes) causes significant human morbidity (>700 million infections
annually) and mortality (>550,000 deaths annually), with a spectrum of infections that range from mild and self-
limiting (e.g. pharyngitis) to severely invasive (e.g. necrotizing fasciitis). We have identified that FasX, the
sRNA component of a novel four-component regulatory system (FasBCAX), post-transcriptionally regulates the
production of key GAS virulence factors. The regulation afforded by the FasBCAX system influences GAS
virulence, enhancing GAS resistance to the bactericidal properties of human blood (see preliminary data) and
lethality in a mouse invasive infection model. However, there remains significant gaps in our knowledge
regarding the functioning of this model regulatory system, including how FasX reduces GAS killing in human
blood by ~30-fold, and how the FasBCA proteins function to enhance fasX expression ~100-fold. We
will fill the regulatory, mechanistic, and virulence gaps in our knowledge by pursuing the following aims:
Aim 1: Determine the mechanism by which FasX enhances GAS resistance to human blood. In this aim,
we will verify our preliminary data that supports the FasX-regulon being twice the size of that currently
appreciated, identify which FasX-regulated virulence factor/s are responsible for the resistance phenotype and
whether their regulation by FasX modifies the binding of host molecules to the GAS cell surface, and, given our
preliminary data that the resistance phenotype occurs via the inhibition of phagocytic cells, test whether
neutrophil activation, phagocytosis, and/or oxidative burst is inhibited.
Aim 2: Determine the mechanism by which the FasBCA proteins enhance FasX sRNA abundance. The
Fas locus consists of the co-transcribed fasBCA and the separately transcribed fasX. FasB and FasC are
homologous to sensor kinases while FasA is homologous to response regulators. Preliminary data are
consistent with FasB and FasC forming heterodimers, rather than homodimers as classically occurs for sensor
kinases. In this aim, we will unravel how the FasBCA proteins interact to enhance the transcription of fasX and
other regulatory targets, and will initiate delineation of host factors capable of modulating Fas system activity.
Completion of this research will greatly expand what is known about sRNA function in GAS, an organism,
along with fellow Lactobacillales pathogens, in which sRNA mechanistic data is limited. We will generate basic
science insights by delineating a never-before-described regulatory system in which two sensor kinases
heterodimerize to activate activity. We will also generate clinical insights by delineating the molecular basis
behind the ability of FasX to inhibit GAS killing in blood, a phenotype that is critical to the ability of this
prevalent human pathogen to cause severe invasive disease.