Functional characterization of ExFadLO, an outer membrane protein required for exporting oxygenated long-chain fatty acids in Pseudomonas aeruginosa

• Published in: Biochimie 2013-02, Vol.95 (2), p.290-298
• Main Authors: Martínez, Eriel, Estupiñán, Mónica, Pastor, F.I. Javier, Busquets, Montserrat, Díaz, Pilar, Manresa, Angeles
• Format: Article
• Language: English
• Subjects: Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Biological Transport; Escherichia coli - genetics; Escherichia coli - metabolism; Extracellular Space - metabolism; FadL family transporters; Fatty Acid Transport Proteins - genetics; Fatty Acid Transport Proteins - metabolism; Gene Expression; Genetic Complementation Test; Hydroxy Acids - metabolism; Mutation; Oleic Acids - metabolism; Outer membrane transport; Oxidation-Reduction; Oxygen - metabolism; Oxygenated fatty acids; Periplasm - metabolism; Phylogeny; Pseudomonas aeruginosa; Pseudomonas aeruginosa - genetics; Pseudomonas aeruginosa - metabolism
• ISSN: 0300-9084; 1638-6183
• DOI: 10.1016/j.biochi.2012.09.032

Bacterial proteins of the FadL family have frequently been associated to the uptake of exogenous hydrophobic substrates. However, their outer membrane location and involvement in substrate uptake have been inferred mainly from sequence similarity to Escherichia coli FadL, the first well-characterized outer membrane transporters of Long-Chain Fatty Acids (LCFAs) in bacteria. Here we report the functional characterization of a Pseudomonas aeruginosa outer membrane protein (ORF PA1288) showing similarities to the members of the FadL family, for which we propose the name ExFadLO. We demonstrate herein that this protein is required to export LCFAs 10-HOME and 7,10-DiHOME, derived from a diol synthase oxygenation activity on oleic acid, from the periplasm to the extracellular medium. Accumulation of 10-HOME and 7,10-DiHOME in the extracellular medium of P. aeruginosa was abolished by a transposon insertion mutation in exFadLO (ExFadLO¯ mutant). However, intact periplasm diol synthase activity was found in this mutant, indicating that ExFadLO participates in the export of these oxygenated LCFAs across the outer membrane. The capacity of ExFadLO¯ mutant to export 10-HOME and 7,10-DiHOME was recovered after complementation with a wild-type, plasmid-expressed ExFadLO protein. A western blot assay with a variant of ExFadLO tagged with a V5 epitope confirmed the location of ExFadLO in the bacterial outer membrane under the experimental conditions tested. Our results provide the first evidence that FadL family proteins, known to be involved in the uptake of hydrophobic substrates from the extracellular environment, also function as secretion elements for metabolites of biological relevance. ► New outer membrane transporter is involved in the export of long-chain oxygenated fatty acids in Pseudomonas aeruginosa. ► The new transporter belongs to the family of FadL protein. ► The new transporter, named exFadLO, exports mono, dihydroxy long chain fatty acids.