The kelch motif and the β-propeller fold. A, Consensus sequence of the kelch motif. Compiled from  and . The sequence motif is shown in relation to the four β-sheets of a propeller blade structure, as determined for the kelch motifs of fungal galactose oxidase . In the consensus, G= glycine, Y = tyrosine, W = tryptophan, s = small residue; l = large residue; h = hydrophobic residue. B, Structure of a kelch-repeat propeller blade. A single blade from the crystal structure of fungal galactose oxidase (1GOF) is shown. β sheets 1–4 are colored as in panel A. The N- and C-termini join to adjacent blades. As indicated by the mapping of the consensus amino acids onto the blade, the most highly-conserved residues are located in the β-sheets. In various examples of β-propeller proteins, the intra- and inter-blade loops have variable sequences and contribute to protein-protein interactions . C, Structure of the kelch-repeat β-propeller domain of fungal galactose oxidase (1GOF). β-sheets 1–4 in each blade are colored as in panel A. As indicated, this β-propeller contains seven blades. The β-4 strand of blade 7 is derived from the amino-terminus of the domain and thus closes the circular structure.