Structural basis of lipoprotein recognition by the bacterial Lol trafficking chaperone LolA

Abstract

In gram-negative bacteria, lipoproteins are vital structural components of the outer membrane (OM) and crucial elements of machineries central to the physiology of the cell envelope. A dedicated apparatus, the Lol system, is required for the correct localization of OM lipoproteins and is essential for viability. The periplasmic chaperone LolA is central to this trafficking pathway, accepting triacylated lipoproteins from the inner membrane transporter LolCDE, before carrying them across the periplasm to the OM receptor LolB. Here, we report a crystal structure of liganded LolA, generated in vivo, revealing the molecular details of lipoprotein association. The structure highlights how LolA, initially primed to receive lipoprotein by interaction with LolC, further opens to accommodate the three ligand acyl chains in a precise conformation within its cavity. LolA forms extensive interactions with the acyl chains but not with any residue of the cargo, explaining the chaperone’s ability to transport structurally diverse lipoproteins. Structural characterization of a ligandedLolA variant incapable of lipoprotein release reveals aberrant association, demonstrating the importance of the LolCDE-coordinated, sequential opening of LolA for inserting lipoprotein in a manner productive for subsequent trafficking. Comparison with existing structures of LolA in complex with LolC or LolCDE reveals substantial overlap of the lipoprotein and LolC binding sites within the LolA cavity, demonstrating that insertion of lipoprotein acyl chains physically disengages the chaperone protein from the transporter by perturbing interaction with LolC. Taken together, our data provide a key step toward a complete understanding of a fundamentally important trafficking pathway.

A comparative analysis of lipoprotein transport proteins – LolA and LolB from Vibro cholerae and LolA from Porphyromonas gingivalis

“…The Nterminal helix, α1, forms the oor of the cleft. The non-polar cleft can interact either with the periplasmic loop of LolC, when uncharged, or the acyl chains of a lipoprotein during protein transportation [18,20]. The helical segment that lls the hydrophobic cavity is comprised of 22 aa in both LolA-PG and LolA-VC but the different position of the helices results in different accessibility to the clefts.…”

“…5b). In in vitro assays it was shown that these compounds induce release of lipoproteins from LolA [20] whereas it is claimed that in vivo targets of these compounds are not LolA or LolB but instead the Mre system [33]. In this study we used ITC to clarify if A22 interacts with recombinant LolA or LolB, when they are not charged with lipoproteins.…”

“…Additionally, LolA from E. coli (LolA-EC) has also been studied in complex with LolC both using crystallography and cryo-electron microscopy [18,19]. These studies were recently supplemented with the X-ray structure of E. coli LolA in complex with a triacylated peptide [20]. Comparatively, LolB, which serves as an attractive drug target against Vibrio parahaemolyticus [21], is less studied, with only the E. coli crystal structure being published [17].…”

ABC Transporters in Bacterial Nanomachineries

“…These findings further underpin the assignment of LolCDE into the group of type VII ABC transporters, as MacB is the founding member of this group [ 24 ]. In a more recent study, the crystal structure of LolA bound to a ligand was also solved by the Koronakis lab [ 150 ]. The structure shows the precise interaction of the acyl chains of the lipoprotein with the hydrophobic cavity in LolA.…”

A comparative analysis of lipoprotein transport proteins: LolA and LolB from Vibrio cholerae and LolA from Porphyromonas gingivalis

“…Additionally, LolA from E. coli (LolA-EC) has also been studied in complex with LolC both using crystallography and cryo-electron microscopy 18 , 19 . These studies were recently supplemented with the X-ray structure of E. coli LolA in complex with a triacylated peptide 20 . Comparatively, LolB, which serves as an attractive drug target against Vibrio parahaemolyticus 21 , is less studied, with only the E. coli crystal structure being published 17 .…”