title: HxcQ liposecretin is self-piloted to the outer membrane by its N-terminal lipid anchor.
abstract: Secretins are an unusual and important class of bacterial outer membrane (OM) proteins. They are involved in the transport of single proteins or macromolecular structures such as pili, needle complexes, and bacteriophages across the OM. Secretins are multimeric ring-shaped structures that form large pores in the OM. The targeting of such macromolecular structures to the OM often requires special assistance, conferred by specific pilotins or pilot proteins. Here, we investigated HxcQ, the OM component of the second Pseudomonas aeruginosa type II secretion system. We found that HxcQ forms high molecular mass structures resistant to heat and SDS, revealing its secretin nature. Interestingly, we showed that HxcQ is a lipoprotein. Construction of a recombinant nonlipidated HxcQ (HxcQnl) revealed that lipidation is essential for HxcQ function. Further phenotypic analysis indicated that HxcQnl accumulates as multimers in the inner membrane of P. aeruginosa, a typical phenotype observed for secretins in the absence of their cognate pilotin. Our observations led us to the conclusion that the lipid anchor of HxcQ plays a pilotin role. The self-piloting of HxcQ to the OM was further confirmed by its correct multimeric OM localization when expressed in the heterologous host Escherichia coli. Altogether, our results reveal an original and unprecedented pathway for secretin transport to the OM.
authors.affiliation: Laboratoire d'Ingénierie des Systèmes Macromoléculaires (UPR 9027), CNRS, Institut de Microbiologie de la Méditerranée, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
authors.forename: Véronique
authors.initials: V
authors.lastname: Viarre
authors.forename: Eric
authors.initials: E
authors.lastname: Cascales
authors.forename: Geneviève
authors.initials: G
authors.lastname: Ball
authors.forename: Gérard P F
authors.initials: GP
authors.lastname: Michel
authors.forename: Alain
authors.initials: A
authors.lastname: Filloux
authors.forename: Romé
authors.initials: R
authors.lastname: Voulhoux
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D001692:Biological Transport; D002499:Centrifugation, Density Gradient; D003902:Detergents / Q000494:pharmacology; D004926:Escherichia coli / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D008074:Lipoproteins / Q000737:chemistry*; D019308:Palmitic Acid / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000378:metabolism; D012633:Secretin / Q000737:chemistry
chemical_list: D001425:Bacterial Outer Membrane Proteins; D003902:Detergents; D008055:Lipids; D008074:Lipoproteins; D010455:Peptides; D012633:Secretin; D019308:Palmitic Acid; C017339:globomycin