FEMA

FemA is a gene found in Staphylococcus aureus that encodes a cytosolic glycine transferase involved in bacterial cell wall synthesis. It is part of the femAB family of enzymes, which also includes FemB, and in related species, FemX, all of which participate in constructing the pentaglycine cross-bridge that links stem peptides in the peptidoglycan of many Gram-positive bacteria. The action of these enzymes is to add glycine residues to the interpeptide bridge, a process that occurs during late stages of peptidoglycan assembly and is essential for proper cross-linking by penicillin-binding proteins.

Function and mechanism: FemA works in concert with FemB (and homologs in other species) to form the mature pentaglycine cross-bridge that connects peptide stems within the cell wall. This cross-bridge is important for the structural integrity and rigidity of the peptidoglycan matrix and influences how PBPs interact with the cell wall during normal growth and during antibiotic stress.

Genetic and clinical relevance: Disruption or impairment of femA reduces the extent of cross-bridge formation, alters the muropeptide composition of the cell wall, and can compromise beta-lactam resistance in mecA-carrying strains. In MRSA and related strains, loss of FemA function is associated with increased susceptibility to beta-lactam antibiotics and changes in cell-wall morphology. Because of its role in cell wall architecture and antibiotic resistance, FemA has been studied as a potential target for strategies aimed at restoring beta-lactam susceptibility.

See also: peptidoglycan, methicillin-resistant Staphylococcus aureus, penicillin-binding proteins, bacterial cell wall biosynthesis.