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

Abstract

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 ␤-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.membrane protein ͉ x-ray structure

Rhizobial homologs of the fatty acid transporter FadL facilitate perception of long-chain acyl-homoserine lactone signals

“…Thus, the sequence of the specificity region might affect the properties of the binding pocket, resulting in different affinities to free fatty acid or AHL. A leucine residue at the position corresponding to K317 has been identified as characteristic of FadL homologs transporting aromatic compounds, but not fatty acids (32). Each FadL homolog analyzed in the present study had a leucine residue at this position irrespective of its ability to support growth on oleic acid, suggesting that the architecture of FadL-binding pockets likely is more heterogeneous than previously assumed.…”

Isolation and molecular characterization of a novel <i>pseudomonas putida</i> strain capable of degrading organophosphate and aromatic compounds

“…It is supplemented by another putative transporter complex, Ttg2, which has been shown to signifycantly increase host tolerance of toluene [66]. Hydrocarbon uptake is mediated by a TodX-like outer membrane channel protein with a hatch domain regulating a passage of hydrophobic compounds to the periplasm [67]. In addition, the strain carries ttg8 gene encoding a conserved protein of unknown function, which plays an important role in resistance to toluene [66].…”

Neisseria meningitidis antigen NMB0088: sequence variability, protein topology and vaccine potential

“…This family includes TodX from Pseudomonas putida F1 and TbuX from Ralstonia pickettii PKO1. These are membrane proteins of uncertain function that are involved in aromatic hydrocarbon biodegradation (Hearn et al, 2008). The family also includes FadL of E. coli involved in translocation of long-chain fatty acids across the outer membrane (Black et al, 1987).…”