Living with an imperfect cell wall: compensation of femAB inactivation in Staphylococcus aureus

Abstract

Background: Synthesis of the Staphylococcus aureus peptidoglycan pentaglycine interpeptide bridge is catalyzed by the nonribosomal peptidyl transferases FemX, FemA and FemB. Inactivation of the femAB operon reduces the interpeptide to a monoglycine, leading to a poorly crosslinked peptidoglycan. femAB mutants show a reduced growth rate and are hypersusceptible to virtually all antibiotics, including methicillin, making FemAB a potential target to restore β-lactam susceptibility in methicillin-resistant S. aureus (MRSA). Cis-complementation with wild type femAB only restores synthesis of the pentaglycine interpeptide and methicillin resistance, but the growth rate remains low. This study characterizes the adaptations that ensured survival of the cells after femAB inactivation.

Raf-Kinase Inhibitor Gw5074 Shows Antibacterial Activity Against Methicillin-Resistant Staphylococcus Aureus and Potentiates the Activity of Gentamicin

“…Inactivation of femAB leads to reduced growth rates and hyper-susceptibility to practically all known antibiotics [51]. However, the inactivation of fmhA and fmhC, but not fmhB, which is involved in the first step of interpeptide formation, had no effect on growth, antibiotic susceptibility or peptidoglycan composition of the cell wall [33].…”

A glyS T-box riboswitch with species-specific structural features responding to both proteinogenic and nonproteinogenic tRNAGly isoacceptors

“…The S. aureus cell wall contains characteristic pentaglycine bridges that stabilize peptidoglycan chain interconnection (Schneider et al 2004). They also represent an example of exoribosomal peptide synthesis catalyzed by a family of three nonribosomal peptidyl-transferases known as Fem factors (Factors Essential for Methicillin Resistance; FemX, A and B) (Rohrer and Berger-Bachi 2003;Hübscher et al 2007;Giannouli et al 2010). As has been shown previously, the five tRNA Gly isoacceptors might serve as either proteinogenic or nonproteinogenic carriers of glycine for the two distinct and metabolically unrelated pathways (Giannouli et al 2009).…”

“…The remaining three molecules, termed NP1, NP2, and NEW (bearing UCC anticodons), potentially escape protein synthesis after glycylation as judged by their weak binding to EF-Tu. In turn, they probably serve as substrates for the formation of the characteristic pentaglycine interconnecting peptides that stabilize the staphylococcal cell wall, a process essential for cell viability (Rohrer and BergerBachi 2003;Schneider et al 2004;Hübscher et al 2007;Giannouli et al 2009Giannouli et al , 2010.…”

Uniformity of Glycyl Bridge Lengths in the Mature Cell Walls of Fem Mutants of Methicillin-Resistant Staphylococcus aureus

“…To confirm that the presence of a heterogeneous PG fragment mixture in intact cells of the FemA mutant is not due to leakage of the point mutation (16,17), we characterized the glycine content in intact cells of the FemAB null mutant and compared the results with those for the FemA mutant. The FemAB null mutant was constructed by a complete inactivation of both the femA and femB genes (20,21). Figure 5 (bottom) shows the overlaid ⌬S Lys-Gly (red line) and ⌬S total (black line) spectra.…”

“…1, bottom). Complete knockout of the femA and femB genes resulted in a FemAB (AS145) null mutant (14,20,21) having a monoglycyl bridge structure, as in the FemA mutant. An additional hidden mutation(s) acquired during the construction in the FemAB null mutant (and possibly present in FemA as well) was suggested previously by Ling and Berger-Bächi (22).…”