Human Group IIA secreted phospholipase A2 (hGIIA) is a highly cationic small protein! important for the innate immune defense against Gram-positive bacteria. The enzyme traverses the thick peptidoglycan layer of Gram-positive bacteria to reach the phospholipid membrane where it catalyzes the hydrolysis of phosphatidylglycerol, ultimately leading to bacterial death through lysis. In comparison to other Gram-positive bacteria, Group A Streptococcus (GAS), or Streptococcus pyogenes is remarkably resistant to hGIIA activity. GAS transposon library screens, designed to identify the genes that provide susceptibility/resistance to hGIIA, uncovered a number of genes involved in biosynthesis and modification of Lancefield group A carbohydrate (GAC) and lipoteichoic acid (LTA), two crucial cell envelope constituents of GAS. GAC is a rhamnose-containing glycopolymer covalently attached to peptidoglycan. Modification of GAC with negatively charged glycerol phosphate as well as the absence of positively-charged D-alanine modifications in LTA drastically compromise GAS survival when challenged with hGIIA. This project seeks to identify the functions of two previously uncharacterized proteins identified by an hGIIA sensitivity screen, a putative GAC hydrolase, GacM, and a GT-C type membrane glycosyltransferase, PgtC. Additionally, we uncovered a GT-A type membrane glycosyltrasferase PgtA that might participate together with PgtC in a protein glycosylation pathway in GAS. We will define the biological functions of these three proteins and their roles in antimicrobial resistance and virulence using a range of genetic, biochemical and analytical approaches. Functional characterization of these novel targets will lead to an increased understanding of how antimicrobial resistance is regulated in all Gram-positive bacteria and how resistance to antimicrobials is emerging among Gram-positive pathogens.
The goal of this project is to identify the functions of two enzymes that provide resistance of Group A Streptococcus (GAS) to Human Group IIA secreted phospholipase A2. Understanding the resistance mechanisms used by GAS will allow developing the novel strategies against GAS infections.
