PDBsum entry 6s8h

Transport protein

PDB id

6s8h

Contents

			Protein chains

					239 a.a.


					239 a.a.


					243 a.a.

			Ligands

					LMN ×2


					JSG


					DCQ ×2


					LMT ×2

References listed in PDB file

Key reference

Title

Cryo-Em structures of lipopolysaccharide transporter lptb₂fgc in lipopolysaccharide or AMP-Pnp-Bound states reveal its transport mechanism.

Authors

X.Tang, S.Chang, Q.Luo, Z.Zhang, W.Qiao, C.Xu, C.Zhang, Y.Niu, W.Yang, T.Wang, Z.Zhang, X.Zhu, X.Wei, C.Dong, X.Zhang, H.Dong.

Ref.

Nat Commun, 2019, 10, 4175. [DOI no: 10.1038/s41467-019-11977-1]

PubMed id

31519889

Abstract

Lipopolysaccharides (LPS) of Gram-negative bacteria are critical for the defence against cytotoxic substances and must be transported from the inner membrane (IM) to the outer membrane (OM) through a bridge formed by seven membrane proteins (LptBFGCADE). The IM component LptB₂FG powers the process through a yet unclarified mechanism. Here we report three high-resolution cryo-EM structures of LptB₂FG alone and complexed with LptC (LptB₂FGC), trapped in either the LPS- or AMP-PNP-bound state. The structures reveal conformational changes between these states and substrate binding with or without LptC. We identify two functional transmembrane arginine-containing loops interacting with the bound AMP-PNP and elucidate allosteric communications between the domains. AMP-PNP binding induces an inward rotation and shift of the transmembrane helices of LptFG and LptC to tighten the cavity, with the closure of two lateral gates, to eventually expel LPS into the bridge. Functional assays reveal the functionality of the LptF and LptG periplasmic domains. Our findings shed light on the LPS transport mechanism.

Secondary reference #1