Surface Export of GAPDH/SDH, a Glycolytic Enzyme, Is Essential for Streptococcus pyogenes Virulence

Abstract

Streptococcal surface dehydrogenase (SDH) (glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) is an anchorless major multifunctional surface protein in group A Streptococcus (GAS) with the ability to bind important mammalian proteins, including plasmin(ogen). Although several biological properties of SDH are suggestive of its possible role in GAS virulence, its direct role in GAS pathogenesis has not been ascertained because it is essential for GAS survival. Thus, it has remained enigmatic as to “how and why” SDH/GAPDH is exported onto the bacterial surface. The present investigation highlights “why” SDH is exported onto the GAS surface. Differential microarray-based genome-wide transcript abundance analysis was carried out using a specific mutant, which was created by inserting a hydrophobic tail at the C-terminal end of SDH (M1-SDHHBtail) and thus preventing its exportation onto the GAS surface. This analysis revealed downregulation of the majority of genes involved in GAS virulence and genes belonging to carbohydrate and amino acid metabolism and upregulation of those related to lipid metabolism. The complete attenuation of this mutant for virulence in the mouse model and the decreased and increased virulence of the wild-type and mutant strains postcomplementation with SDHHBtail and SDH, respectively, indicated that the SDH surface export indeed regulates GAS virulence. M1-SDHHBtail also displayed unaltered growth patterns, increased intracellular ATP concentration and Hpr double phosphorylation, and significantly reduced pH tolerance, streptolysin S, and SpeB activities. These phenotypic and physiological changes observed in the mutant despite the unaltered expression levels of established transcriptional regulators further highlight the fact that SDH interfaces with many regulators and its surface exportation is essential for GAS virulence.

Structure and activity of theStreptococcus pyogenesfamily GH1 6-phospho-β-glucosidase SPy1599

“…Arguing against this is the absence of signal peptides from all of these proteins, apart from EndoS, implying cytoplasmic location (Sheldon et al, 2006;Suits et al, 2010). Conversely, there are also recent data showing that other S. pyogenes proteins with no discernible secretion sequence are indeed known to exist in an extracellular location (Jin et al, 2011;Pancholi & Fischetti, 1998), so one must acknowledge the possibility of a previously uncharacterized protein-export system in S. pyogenes (Pancholi & Fischetti, 1998). Whilst an uncharacterized protein-export machinery may play a role, there is however little direct evidence to support such a role for these enzymes in N-glycan degradation.…”

Role of Serine/Threonine Phosphatase (SP-STP) in Streptococcus pyogenes Physiology and Virulence

“…Total fatty acid content and the composition of individual fatty acids in the wild-type and mutant strain of M1SF370 were custom analyzed by gas chromatography (Microbial ID) as described (24). The fatty acid profiles were analyzed with the Sherlock pattern recognition software.…”

Export Requirements of Pneumolysin in Streptococcus pneumoniae

“…Enolase has been shown to reassociate with the cell surface (5), leaving open the possibility that a limited number of cells lyse and release their cytoplasmic contents, which then stick to the surfaces of nearby intact, unlysed cells. However, a recent study analyzing the localization of SDH in S. pyogenes showed that the protein could be held inside the cell with a hydrophobic tail, lending support to the hypothesis that there is a dedicated export pathway for this protein (16). Here we show that exogenous Ply that has been released by autolysis cannot reassociate with cells.…”

“…There are several examples of streptococcal proteins that localize to the cell wall despite lacking a signal sequence or cell wall-anchoring motif (16,22,23). Among them, enolase has been shown to reassociate with the surface of S. pneumoniae (5).…”

“…There are other proteins lacking a recognizable signal sequence or cell wall anchoring motif that "moonlight" on the bacterial surface, such as enolase and streptococcal surface GAPDH (SDH) (5,16,22,23). Enolase has been shown to reassociate with the cell surface (5), leaving open the possibility that a limited number of cells lyse and release their cytoplasmic contents, which then stick to the surfaces of nearby intact, unlysed cells.…”