The CarO porin is slightly cation-selective and can be mutated to give rise to imipenem-resistance (Zhu et al. 2019). It is of 243 aas (Siroy et al. 2005) and plays a role in cabapenum resistance (Fonseca et al. 2013) as well as MDR (Yang et al. 2015).  It has been implicated in the uptake of ornithine as well as carbapenem antibiotics. Zahn et al. 2015 reported crystal structures of three isoforms of CarO. The structures show a monomeric eight-stranded barrel lacking an open channel. CarO has a substantial extracellular domain resembling a glove that contains all the divergent residues between the different isoforms. A6XB80 is another isoform with 77% identity to the one listed here in TCDB. Overexpression of carO is associated with carbapenem resistance (AlQumaizi et al. 2022).