Pius S. Padayatti, Sung Chang Lee, Robyn L. Stanfield, Po-Chao Wen, Emad
Tajkhorshid, Ian A. Wilson, and Qinghai Zhang.
Structural insights into the lipid A transport pathway in MsbA.
Structure, 27:1114-1123, 2019.
(PMC: PMC6610721)
PADA2019-ET
MsbA is an essential ATP-binding cassette transporter in Gram-negative
bacteria that transports lipid A and lipopolysaccharide from the cytoplasmic
leaflet to the periplasmic leaflet of the inner membrane. Here we report the X-
ray structure of MsbA from Salmonella typhimurium at 2.8-Å resolution in an
inward-facing conformation after cocrystallization with lipid A and using a
stabilizing facial amphiphile. The structure displays a large amplitude opening
in the transmembrane portal, which is likely required for lipid A to pass from its
site of synthesis into the protein-enclosed transport pathway. Putative lipid A
density is observed further inside the transmembrane cavity, consistent with a
trap and flip model. Additional electron density attributed to lipid A is observed
near an outer surface cleft at the periplasmic ends of the transmembrane
helices. These findings provide new structural insights into the lipid A transport
pathway through comparative analysis with existing MsbA structures.
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