The OprB family includes the Pseudomonas aeruginosa porin B (OprB), a substrate-selective channel for a variety of different sugars, which is probably restricted to carbohydrates and facilitates glucose fusion across the outer membrane. Homologs are also found in Pseudomonas chlororaphis, Burkholderia cepacia, Pseudomonas fluorescens, Acinetobacter calcoaceticus and Xanthomonas campestris. The high-affinity glucose transport system is primarily specific for glucose and well conserved, although the outer membrane components may differ in channel architecture and specificity for other carbohydrates. OprB forms a monomeric, 16-stranded ß-barrel with a constriction formed by extracellular loops L2 and L3. The side chains of two highly conserved arginine residues (Arg(83) and Arg(110)) and a conserved glutamate (Glu(106)) line the channel constriction and interact with a bound glucose molecule.

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