TCB Publications - Abstract

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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