The outer membrane (OM) of Gram-negative bacteria serves as a selective permeability barrier that allows entry of essential nutrients while excluding toxic compounds, including antibiotics. The OM is asymmetric and contains an outer leaflet of lipopolysaccharides (LPS) or lipooligosaccharides (LOS) and an inner leaflet of glycerophospholipids (GPL). We screened Acinetobacter baumannii transposon mutants and identified a number of mutants with OM defects, including an ABC transporter system homologous to the Mla system in E. coli. We further show that this opportunistic, antibiotic-resistant pathogen uses this multicomponent protein complex and ATP hydrolysis at the inner membrane to promote GPL export to the OM. The broad conservation of the Mla system in Gram-negative bacteria suggests the system may play a conserved role in OM biogenesis. The importance of the Mla system to Acinetobacter baumannii OM integrity and antibiotic sensitivity suggests that its components may serve as new antimicrobial therapeutic targets.
The cryo-EM map has been deposited in the Electron Microscopy Data Bank with accession code EMD-8738 (8.7 Å map). The coordinates for the MlaBDEF model have been deposited to PDB, accession code 6IC4.
- Samuel I Miller
- Justin M Kollman
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Tâm Mignot, Aix Marseille University-CNRS UMR7283, France
© 2019, Kamischke et al.
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