Our work reveals unique structural features of the entire MlaFEDB complex, six well-resolved phospholipids in three distinct cavities, and large-scale conformational changes upon ATP binding. Here we determined three cryo-EM structures of MlaFEDB from Escherichia coli in its nucleotide-free and ATP-bound conformations, and performed extensive functional studies to verify and extend our findings from structural analyses. However, the mechanism of phospholipid translocation remains elusive. The conserved MlaFEDB complex in the inner membrane functions as an ABC transporter to drive the translocation of phospholipids between the inner membrane and the periplasmic protein MlaC. Understanding the mechanisms of phospholipid translocation between the inner and outer membrane represents one of the major challenges surrounding bacterial phospholipid homeostasis. Gangliosides are most prevalent in the outer membranes of nerve cells, although they also occur in smaller quantities in the outer membranes of most other cells.In Gram-negative bacteria, phospholipids are major components of the inner membrane and the inner leaflet of the outer membrane, playing an essential role in forming the unique dual-membrane barrier to exclude the entry of most antibiotics. Most cell-to-cell recognition and communication processes (e.g., blood group antigens) depend on differences in the sequences of sugars in these compounds. Because of considerable variation in their sugar components, about 130 varieties of gangliosides have been identified. The sphingolipids called gangliosides are more complex, usually containing a branched chain of three to eight monosaccharides and/or substituted sugars. Cerebrosides are sphingolipids that contain a sugar unit.
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