Murgocil is a Highly Bioactive Staphylococcal-Specific Inhibitor of the Peptidoglycan Glycosyltransferase Enzyme MurG

Abstract

Modern medicine is founded on the discovery of penicillin and subsequent small molecules that inhibit bacterial peptidoglycan (PG) and cell wall synthesis. However, the discovery of new chemically and mechanistically distinct classes of PG inhibitors has become exceedingly rare, prompting speculation that intracellular enzymes involved in PG precursor synthesis are not 'druggable' targets. Here, we describe a β-lactam potentiation screen to identify small molecules that augment the activity of β-lactams against methicillin-resistant Staphylococcus aureus (MRSA) and mechanistically characterize a compound resulting from this screen, which we have named murgocil. We provide extensive genetic, biochemical, and structural modeling data demonstrating both in vitro and in whole cells that murgocil specifically inhibits the intracellular membrane-associated glycosyltransferase, MurG, which synthesizes the lipid II PG substrate that penicillin binding proteins (PBPs) polymerize and cross-link into the cell wall. Further, we demonstrate that the chemical synergy and cidality achieved between murgocil and the β-lactam imipenem is mediated through MurG dependent localization of PBP2 to the division septum. Collectively, these data validate our approach to rationally identify new target-specific bioactive β-lactam potentiation agents and demonstrate that murgocil now serves as a highly selective and potent chemical probe to assist our understanding of PG biosynthesis and cell wall biogenesis across Staphylococcal species.

The sentinel role of peptidoglycan recycling in the β-lactam resistance of the Gram-negative Enterobacteriaceae and Pseudomonas aeruginosa

“…Nor are these peptidoglycan pathways the only pathways that synergize with the β-lactam antibiotics [111]. Exploratory validation of β-lactam synergy has been achieved in Gram-positive bacteria by the pairing of β-lactams with an inhibitor of peptidoglycan biosynthesis [112], an inhibitor of cytoskeleton assembly [113], and inhibitors of wall teichoic acid assembly [114–118]. Similar points of intervention certainly will be found with respect to the envelope of the Gram-negative bacterium.…”

Small cationic antimicrobial peptides delocalize peripheral membrane proteins

“…Delocalization of MurG could explain the effects on cell-wall biosynthesis and integrity exerted by MP196. This enzyme recently was shown to be the direct target of the anti-staphylococcal small molecule inhibitor murgocil (47).…”

Peptidoglycan synthesis drives an FtsZ-treadmilling-independent step of cytokinesis

“…The strategy to construct ColFemX-sGFP was essentially the same, except that the pFAST3 32 vector was used instead of pSG5082. A femX fragment was amplified from COL DNA with primers femXg_P1 and femXg_P2, digested with Kpn I/ Xho I and cloned into pFAST3 upstream and in frame with sgfp, giving pFAST-femX, which was electroporated into RN4220 and transduced into COL. Strain ColMurG-GFP was obtained by transducing the murG-gfp construct from BCBMS001 33 into COL.…”