LetB Structure Reveals a Tunnel for Lipid Transport across the Bacterial Envelope.

Georgia L Isom, Nicolas Coudray, Mark R MacRae, Collin T McManus, Damian C Ekiert, Gira Bhabha

Cell 2020 Apr 30

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Gram-negative bacteria are surrounded by an outer membrane composed of phospholipids and lipopolysaccharide, which acts as a barrier and contributes to antibiotic resistance. The systems that mediate phospholipid trafficking across the periplasm, such as MCE (Mammalian Cell Entry) transporters, have not been well characterized. Our ~3.5 Å cryo-EM structure of the E. coli MCE protein LetB reveals an ~0.6 megadalton complex that consists of seven stacked rings, with a central hydrophobic tunnel sufficiently long to span the periplasm. Lipids bind inside the tunnel, suggesting that it functions as a pathway for lipid transport. Cryo-EM structures in the open and closed states reveal a dynamic tunnel lining, with implications for gating or substrate translocation. Our results support a model in which LetB establishes a physical link between the two membranes and creates a hydrophobic pathway for the translocation of lipids across the periplasm. Copyright © 2020 Elsevier Inc. All rights reserved.

Citation

Georgia L Isom, Nicolas Coudray, Mark R MacRae, Collin T McManus, Damian C Ekiert, Gira Bhabha. LetB Structure Reveals a Tunnel for Lipid Transport across the Bacterial Envelope. Cell. 2020 Apr 30;181(3):653-664.e19