Forms pores that allow passive diffusion of cations across the outer membrane. Part of a cation efflux system that mediates resistance to copper and silver (By similarity). Homotrimer. Component of the cus efflux system composed of CusA, CusB, CusC and CusF (By similarity). Transcriptionally regulated by CusR in response to copper and silver ions. Belongs to the outer membrane factor (OMF) (TC 1.B.17) family.