Synthetic Lethal Compound Combinations Reveal a Fundamental Connection between Wall Teichoic Acid and Peptidoglycan Biosyntheses in Staphylococcus aureus

Abstract

Methicillin resistance in Staphylococcus aureus depends on the production of mecA, which encodes penicillin-binding protein 2A (PBP2A), an acquired peptidoglycan transpeptidase (TP) with reduced susceptibility to beta-lactam antibiotics. PBP2A crosslinks nascent peptidoglycan when the native TPs are inhibited by beta-lactams. Although mecA expression is essential for beta-lactam resistance, it is not sufficient. Here we show that blocking the expression of wall teichoic acids (WTAs) by inhibiting the first enzyme in the pathway, TarO, sensitizes MRSA strains to beta-lactams even though the beta-lactam-resistant transpeptidase, PBP2A, is still expressed. The dramatic synergy between TarO inhibitors and beta-lactams is noteworthy not simply because strategies to overcome methicillin-resistant S. aureus (MRSA) are desperately needed, but because neither TarO nor the activities of the native TPs are essential in MRSA strains. The “synthetic lethality” of inhibiting TarO and the native TPs suggests a functional connection between ongoing WTA expression and peptidoglycan assembly in S. aureus. Indeed, transmission electron microscopy shows that S. aureus cells blocked in WTA synthesis have extensive defects in septation and cell separation, indicating dysregulated cell wall assembly and degradation. Our studies imply that WTAs play a fundamental role in S. aureus cell division and raise the possibility that synthetic lethal compound combinations may have therapeutic utility for overcoming antibiotic resistant bacterial infections.

Dual Targeting of Cell Wall Precursors by Teixobactin Leads to Cell Lysis

“…In the absence of WTA, Atl binding on the cell surface is delocalized, causing lysis (21). Furthermore, WTA are required for ␤-lactam resistance in methicillin-resistant S. aureus, and the cells which lack WTA are sensitized to ␤-lactam-induced cell lysis (26)(27)(28). The genes involved in teichoic acid biosynthesis are called the tar genes (for teichoic acid ribitol).…”

“…As teixobactin blocks lipid II and lipid III, this suggests that the lytic activity of teixobactin is due to the combined inhibition of both targets. To further examine a potential synergistic relationship between inhibition of peptidoglycan and teichoic acid biosynthesis, we examined the bactericidal and lytic activity of vancomycin with tunicamycin, a known inhibitor of WTA synthesis against cultures of the S. aureus laboratory strain HG003 (27) (Fig. 3C and D).…”

Methicillin resistance in Staphylococcus aureus requires glycosylated wall teichoic acids

“…Preventing wall teichoic acid (WTA) synthesis by blocking TarO, which catalyzes the first step in the WTA pathway, sensitizes MRSA to β-lactams (11,12). S. aureus WTAs are covalently attached to PG and consist of a poly(ribitol phosphate) [poly (RboP)] backbone containing three tailoring modifications: Dalanylation, α-O-GlcNAcylation, and β-O-GlcNAcylation ( Fig.…”

Inhibition of phospho-MurNAc-pentapeptide translocase (MraY) by nucleoside natural product antibiotics, bacteriophage ϕX174 lysis protein E, and cationic antibacterial peptides

“…Interest in teichoic acid biosynthetic enzymes as antibacterial targets has been enhanced by the discovery that teichoic acid biosynthetic genes are essential for S. aureus nasal colonisation [16]. Campbell et al have shown that inhibition of TarO with tunicamycin sensitises methicillin-resistant S. aureus strains to beta-lactam antibiotics, implying a fundamental connection between teichoic acid biosynthesis and peptidoglycan assembly in S. aureus [17]. Other homologues in this phospho-sugar transferase family include a glucose-1-phosphate transferase WcaJ involved in colonic acid capsule biosynthesis in E. coli and C. crescentus [18], and transferase WcfS involved in B. fragilis capsular polysaccharide biosynthesis [19].…”