This family consists of homologs to OmpW protein of Salmonella typhimurium, Escherichia coli and Vibrio cholerae (minor outer membrane proteins) and the major outer membrane protein OprG of Pseudomonas aeruginosa. OprG appears to be involved in low-affinity iron uptake and transport hydrophobic compounds by using a lateral gate in the barrel wall thought to be lined by three conserved prolines, whereas OmpW is also the Receptor for colicin S4. AlkL, a minimalistic outer-membrane protein from oil-consuming bacteria, exploits dynamics of extracellular loops to channel substrate across the polysaccharide barrier and into the hydrophobic interior of the outer membrane. Homologs have been found in many Gram-negative bacterial genera including Azotobacter, Desulfitobacterium, Burkholderia, Xanthomonas, Rhodobacter, Ralstonia, Delftia and Rickettsia. Proteins of the family show low sequence similarity to members of the OprF family, while the structures of both OmpW of Escherichia coli and OprG from Pseudomonas aeruginosa, revealed an 8-stranded ß-barrel.

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