Outer-membrane transport of aromatic hydrocarbons as a first step in biodegradation

• Published in: Proceedings of the National Academy of Sciences - PNAS 2008-06, Vol.105 (25), p.8601-8606
• Main Authors: Hearn, Elizabeth M, Patel, Dimki R, van den Berg, Bert
• Format: Article
• Language: English
• Subjects: AROMATICS; Bacterial Outer Membrane Proteins - chemistry; Bacterial Outer Membrane Proteins - metabolism; Binding Sites; BIODEGRADATION; Biodegradation, Environmental; Biological Sciences; Biological Transport; CARBOXYLIC ACIDS; CELL MEMBRANES; CRYSTAL STRUCTURE; Crystallography, X-Ray; Crystals; DETERGENTS; E coli; ESCHERICHIA COLI; Escherichia coli - genetics; Escherichia coli - metabolism; Fatty acids; HYDROCARBONS; Hydrocarbons, Aromatic - metabolism; IN VIVO; MATERIALS SCIENCE; MEMBRANE PROTEINS; Membranes; Models, Molecular; Molecular structure; Molecules; national synchrotron light source; Protein Structure, Tertiary; Proteins; PSEUDOMONAS; Pseudomonas putida; Pseudomonas putida - metabolism; Ralstonia pickettii; Ralstonia pickettii - metabolism; RESIDUES; Substrate Specificity; SUBSTRATES; TRANSPORT
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0801264105

Bacterial biodegradation of hydrocarbons, an important process for environmental remediation, requires the passage of hydrophobic substrates across the cell membrane. Here, we report crystal structures of two outer membrane proteins, Pseudomonas putida TodX and Ralstonia pickettii TbuX, which have been implicated in hydrocarbon transport and are part of a subfamily of the FadL fatty acid transporter family. The structures of TodX and TbuX show significant differences with those previously determined for Escherichia coli FadL, which may provide an explanation for the substrate-specific transport of TodX and TbuX observed with in vivo transport assays. The TodX and TbuX structures revealed 14-stranded β-barrels with an N-terminal hatch domain blocking the barrel interior. A hydrophobic channel with bound detergent molecules extends from the extracellular surface and is contiguous with a passageway through the hatch domain, lined by both hydrophobic and polar or charged residues. The TodX and TbuX structures support a mechanism for transport of hydrophobic substrates from the extracellular environment to the periplasm via a channel through the hatch domain.