Role of the Arginine Deiminase Pathway in the Survival of Group A Streptococcus in the Phagolysosome

Abstract

Group A Streptococcus (GAS) is a Gram positive bacterial species responsible for infections ranging from localized to invasive and lead to more than 500,000 deaths per year. When macrophages are infected by GAS, the cell actively brings bacteria into its phagosome. The phagosome fuses with lysosome, which becomes acidified and activates proteolytic enzymes to subsequently eliminate bacteria. We have developed a GAS strain expressing a pH‐sensitive green fluorescent protein and found that the protein was successfully degraded at a pH lower than 6. However, the fluorescent signal is not degraded when GAS is in macrophage phagolysosomes, indicating that GAS prevents lysosome acidification, enhancing its intracellular survival. We are currently examining the role of Arc enzymes that are involved in the arginine deiminase (ADI) pathway in preventing lysosomal acidification. GAS uses ADI pathway to catabolize hosts' arginine and convert it to ammonia and ATP, which could act as an acid buffer in the lysosome. In the ADI pathway, the ArcC protein is a carbamate kinase, a necessary protein in producing ammonia. ArcD encodes the anti‐porter of arginine and ornithine, and is important to bring in substrate and export by‐products. Using a cell killing assay, we found that GAS mutant strains lacking ArcC and ArcD proteins (ΔArcC and ΔArcD) survived less well upon infection of THP‐1 macrophage cells. Immunofluorescence data indicates all three strains traffic normally through the phagocytic pathway. We are currently assessing whether the ΔArcC and ΔArcD strains prevent phagolysosomal acidification using the pH‐sensitive green fluorescent protein as a probe. A better understanding on the crucial enzymes that prevent lysosome acidification provides insights for developing drug targets and partially reveals the mechanism that enhances GAS intracellular survival.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.