The OprD family includes a number of porins in Pseudomonas species and other Gram-negative bacteria that appear to exhibit a variety of substrate specificities. OprD facilitates the diffusion of basic amino acids as well as some structurally analogous beta-lactam antibiotics like imipenem. Mutational inactivation of the oprD gene is associated with carbapenem resistance in Pseudomonas aeruginosa, whereas the C-terminal portion of OprD and, in particular, the hypothetical loop L7, was responsible for the unusual meropenem hypersusceptibility. There is also evidence that OprD porin of Pseudomonas aeruginosa bears protease activity with the catalytic activity established in residues His156, Asp208, and Ser296. However, not all family members have these residues conserved, suggesting that are not all enzymes. Various proteins of the family have shown different specificities in the uptake of metabolites including glycine-glutamate, histidine, proline, tyrosine, cis-aconitate and pyroglutamate. X-ray crystal structure of OprD from Pseudomonas aeruginosa has revealed a monomeric 18-stranded ß-barrel.

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