Structure of bacterial phospholipid transporter MlaFEDB with substrate bound

Elife. 2020 Nov 25:9:e62518. doi: 10.7554/eLife.62518.


In double-membraned bacteria, phospholipid transport across the cell envelope is critical to maintain the outer membrane barrier, which plays a key role in virulence and antibiotic resistance. An MCE transport system called Mla has been implicated in phospholipid trafficking and outer membrane integrity, and includes an ABC transporter, MlaFEDB. The transmembrane subunit, MlaE, has minimal sequence similarity to other transporters, and the structure of the entire inner-membrane MlaFEDB complex remains unknown. Here, we report the cryo-EM structure of MlaFEDB at 3.05 Å resolution, revealing distant relationships to the LPS and MacAB transporters, as well as the eukaryotic ABCA/ABCG families. A continuous transport pathway extends from the MlaE substrate-binding site, through the channel of MlaD, and into the periplasm. Unexpectedly, two phospholipids are bound to MlaFEDB, suggesting that multiple lipid substrates may be transported each cycle. Our structure provides mechanistic insight into substrate recognition and transport by MlaFEDB.

Keywords: E. coli; bacterial outer membrane; cryo-EM; lipid transport; mla pathway; molecular biophysics; structural biology.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / chemistry*
  • ATP-Binding Cassette Transporters / metabolism
  • ATP-Binding Cassette Transporters / ultrastructure*
  • Bacterial Outer Membrane / chemistry
  • Bacterial Outer Membrane / metabolism
  • Bacterial Outer Membrane / ultrastructure
  • Biological Transport, Active / physiology
  • Cryoelectron Microscopy
  • Escherichia coli
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / metabolism
  • Escherichia coli Proteins / ultrastructure*
  • Protein Conformation


  • ATP-Binding Cassette Transporters
  • Escherichia coli Proteins