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Characterization of fmtA, a gene that modulates the expression of methicillin resistance in Staphylococcus aureus
H Komatsuzawa1, K Ohta, H Labischinski
1Department of Microbiology, Hiroshima University School of Dentistry, Kasumi 1-2-3, Minami-ku, Hiroshima City, Hiroshima 734-8553, Japan. hkomatsu@ipc.hiroshima-u.ac.jp
Abstract:
FmtA is a factor which affects the methicillin resistance level in methicillin-resistant Staphylococcus aureus. Since FmtA has two of three conserved motifs which are typically found in penicillin-binding proteins (PBPs) and beta-lactamases, we investigated the penicillin-binding activity of recombinant FmtA and found no such activity. Immunoblotting analysis revealed that FmtA localizes in the membrane fraction. To investigate the function of FmtA, high-pressure liquid chromatography analysis of cell wall muropeptides was performed with an fmtA-inactivated mutant and its parent. The mutant showed a reduced cross-linking and partially reduced amidation of glutamate residues in the peptidoglycan of the mutant. The transcription of fmtA was dose dependently increased by the addition of beta-lactam antibiotics, fosfomycin, and bacitracin, while its transcription was not changed by the addition of vancomycin or tetracycline. These results reveal that Fmt is a membrane-located, non-penicillin-binding protein and that mutation of fmtA affects the cell wall structure, although its precise function is still unknown.
Insights
FmtA, a membrane protein in methicillin-resistant Staphylococcus aureus, does not bind penicillin but impacts cell wall structure. Inactivating fmtA alters peptidoglycan cross-linking and amidation.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- FmtA is implicated in methicillin resistance in Staphylococcus aureus.
- FmtA possesses motifs similar to penicillin-binding proteins (PBPs) and beta-lactamases.
Purpose of the Study:
- To investigate the biochemical activity and cellular function of FmtA.
- To determine if FmtA exhibits penicillin-binding activity.
Main Methods:
- Recombinant FmtA protein was analyzed for penicillin-binding activity.
- Immunoblotting was used to determine FmtA localization.
- High-pressure liquid chromatography (HPLC) analyzed cell wall muropeptides from an fmtA mutant and parent strain.
- fmtA gene transcription was measured under various antibiotic treatments.
Main Results:
- Recombinant FmtA showed no penicillin-binding activity.
- FmtA was localized to the membrane fraction.
- The fmtA-inactivated mutant exhibited reduced peptidoglycan cross-linking and partial glutamate amidation reduction.
- fmtA transcription increased dose-dependently with beta-lactam antibiotics, fosfomycin, and bacitracin.
Conclusions:
- FmtA is a membrane-associated protein that does not bind penicillin.
- FmtA plays a role in Staphylococcus aureus cell wall peptidoglycan structure.
- The precise function of FmtA in antibiotic resistance and cell wall metabolism requires further investigation.