the n-terminus of several kelch proteins contain other protein domains, including discoidin, f-box, and broad-complex, tramtrack, bric-a-brac/poxvirus and zincfinger (btb/poz) domains. kelch proteins may also only have a β-propeller architecture. the btb domain of kelch proteins (if present) allows the formation of homo- or heterodimers that mediate protein–protein interactions.