Phylogenetic, Structural and Functional Relationships between WD‑ and Kelch‑Repeat Proteins
Andrew M. Hudson and Lynn Cooley
The β‑propeller domain is a widespread protein organizational motif. Typically, β‑propeller proteins are encoded by repeated sequences where each repeat unit corresponds to a twisted β‑sheet structural motif; these β‑sheets are arranged in a circle around a central axis to generate the β‑propeller structure. Two superfamilies of β‑propeller proteins, the WD‑repeat and Kelch‑repeat families, exhibit similarities not only in structure, but, remarkably, also in the types of molecular functions they perform. While it is unlikely that WD and Kelch repeats evolved from a common ancestor, their evolution into diverse families of similar function may reflect the evolutionary advantages of the stable core β‑propeller fold. In this chapter, we examine the relationships between these two widespread protein families, emphasizing recently published work relating to the structure and function of both Kelch and WD‑repeat proteins.