Kelch protein

Kelch proteins (and Kelch-like proteins) are a widespread group of proteins that contain multiple Kelch motifs. The kelch domain generally occurs as a set of five to seven kelch tandem repeats that form a β-propeller tertiary structure. Kelch-repeat β-propellers are generally involved in protein–protein interactions, though the large diversity of domain architectures and limited sequence identity between kelch motifs make characterisation of the kelch superfamily difficult. 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. The C-terminus of Kelch proteins contains kelch repeats. Each kelch repeat is a sequence of 44–55 amino acids in length, usually occurring in clusters of 4 – 7 repeats. Each kelch repeat forms a 'blade' of the β-propeller fold, consisting of a four-stranded antiparallel β-sheet secondary structure, arranged radially around a central axis, packed onto its adjoining repeats via hydrophobic contacts. Kelch-repeat β-propellers undergo a variety of binding interactions with other proteins, notably the actin filaments of a cell.