Peptide Deformylase in Staphylococcus aureus : Resistance to Inhibition Is Mediated by Mutations in the Formyltransferase Gene

Peptide deformylase, a bacterial enzyme, represents a novel target for antibiotic discovery. Two deformylase homologs, defA and defB , were identified in Staphylococcus aureus . The defA homolog, located upstream of the transformylase gene, was identified by genomic analysis and was cloned from chromosomal DNA by PCR. A distinct homolog, defB , was cloned from an S. aureus genomic library by complementation of the arabinose-dependent phenotype of a P BAD -def Escherichia coli strain grown under arabinose-limiting conditions. Overexpression in E. coli of defB , but not defA , correlated to increased deformylase activity and decreased susceptibility to actinonin, a deformylase-specific inhibitor. The defB gene could not be disrupted in wild-type S. aureus , suggesting that this gene, which encodes a functional deformylase, is essential. In contrast, the defA gene could be inactivated; the function of this gene is unknown. Actinonin-resistant mutants grew slowly in vitro and did not show cross-resistance to other classes of antibiotics. When compared to the parent, an actinonin-resistant strain produced an attenuated infection in a murine abscess model, indicating that this strain also has a growth disadvantage in vivo. Sequence analysis of the actinonin-resistant mutants revealed that each harbors a loss-of-function mutation in the fmt gene. Susceptibility to actinonin was restored when the wild-type fmt gene was introduced into these mutant strains. An S. aureus Δ fmt strain was also resistant to actinonin, suggesting that a functional deformylase activity is not required in a strain that lacks formyltransferase activity. Accordingly, the defB gene could be disrupted in an fmt mutant.