7ch7

From Proteopedia

Cryo-EM structure of E.coli MlaFEB

Structural highlights

7ch7 is a 6 chain structure with sequence from Escherichia coli K-12. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
Method:	Electron Microscopy, Resolution 3.9Å
Resources:	FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT

Function

MLAE_ECOLI Part of the ABC transporter complex MlaFEDB, which is involved in a phospholipid transport pathway that maintains lipid asymmetry in the outer membrane by retrograde trafficking of phospholipids from the outer membrane to the inner membrane. Probably responsible for the translocation of the substrate across the membrane.^[1] ^[2]

Publication Abstract from PubMed

The outer membrane (OM) of Gram-negative bacteria, which consists of lipopolysaccharides (LPS) in the outer leaflet and phospholipids (PLs) in the inner leaflet, plays a key role in antibiotic resistance and pathogen virulence. The maintenance of lipid asymmetry (Mla) pathway is known to be involved in PL transport and contributes to the lipid homeostasis of the OM, yet the underlying molecular mechanism and the directionality of PL transport in this pathway remain elusive. Here, we reported the cryo-EM structures of the ATP-binding cassette (ABC) transporter MlaFEBD from P. areuginosa, the core complex in the Mla pathway, in nucleotide-free (apo)-, ADP (ATP + vanadate)- and ATP (AMPPNP)-bound states as well as the structures of MlaFEB from E. coli in apo- and AMPPNP-bound states at a resolution range of 3.4-3.9 A. The structures show that the MlaFEBD complex contains a total of twelve protein molecules with a stoichiometry of MlaF(2)E(2)B(2)D(6), and binds a plethora of PLs at different locations. In contrast to canonical ABC transporters, nucleotide binding fails to trigger significant conformational changes of both MlaFEBD and MlaFEB in the nucleotide-binding and transmembrane domains of the ABC transporter, correlated with their low ATPase activities exhibited in both detergent micelles and lipid nanodiscs. Intriguingly, PLs or detergents appeared to relocate to the membrane-proximal end from the distal end of the hydrophobic tunnel formed by the MlaD hexamer in MlaFEBD upon addition of ATP, indicating that retrograde PL transport might occur in the tunnel in an ATP-dependent manner. Site-specific photocrosslinking experiment confirms that the substrate-binding pocket in the dimeric MlaE and the MlaD hexamer are able to bind PLs in vitro, in line with the notion that MlaFEBD complex functions as a PL transporter.

Structural Insight into Phospholipid Transport by the MlaFEBD Complex from P. aeruginosa.,Zhou C, Shi H, Zhang M, Zhou L, Xiao L, Feng S, Im W, Zhou M, Zhang X, Huang Y J Mol Biol. 2021 Jun 25;433(13):166986. doi: 10.1016/j.jmb.2021.166986. Epub 2021 , May 11. PMID:33845086^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

References

↑ Malinverni JC, Silhavy TJ. An ABC transport system that maintains lipid asymmetry in the gram-negative outer membrane. Proc Natl Acad Sci U S A. 2009 May 12;106(19):8009-14. doi:, 10.1073/pnas.0903229106. Epub 2009 Apr 21. PMID:19383799 doi:http://dx.doi.org/10.1073/pnas.0903229106
↑ Thong S, Ercan B, Torta F, Fong ZY, Wong HY, Wenk MR, Chng SS. Defining key roles for auxiliary proteins in an ABC transporter that maintains bacterial outer membrane lipid asymmetry. Elife. 2016 Aug 16;5:e19042. PMID:27529189 doi:10.7554/eLife.19042
↑ Zhou C, Shi H, Zhang M, Zhou L, Xiao L, Feng S, Im W, Zhou M, Zhang X, Huang Y. Structural Insight into Phospholipid Transport by the MlaFEBD Complex from P. aeruginosa. J Mol Biol. 2021 Jun 25;433(13):166986. PMID:33845086 doi:10.1016/j.jmb.2021.166986