This family consists of several bacterial copper resistance proteins. Copper is essential as it serves as co-factor for a variety of enzymes. However, excess of copper is toxic and leads to radical formation and oxidation of biomolecules. CopB serves to extrude copper when it approaches toxic levels. The protein CopB is located in the outer membrane, and seems to form a ß-barrel. The relatively small N-terminal domain is predicted to be periplasmic, suggesting a structural resemblance with TonB dependent receptors, however no sequence homology is apparent.