This family includes several distantly related outer membrane proteins, sequenced from different bacterial species. The family is named after the Escherichia coli FadL protein which functions in transporting long chain fatty acids across the outer membrane. Other members (such as XylN and TodX) are implicated in the transport of aromatic compounds such as toluene, m-xylene and its analogs. All members seem to function as monomers. The 3D structure of FadL at high resolution shows that the protein forms a monomeric ß-barrel composed of 14 beta strands, that is occluded by a central hatch domain. The hatch domain is composed of residues in the N-terminus in a similar manner with that found in the TonB-dependent receptors. The hydrophobic compounds probably bind to multiple sites in the channel and use a transport mechanism that involves a spontaneous conformational change in the hatch region.

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