Kelch is a 50-residue motif, named after the Drosophila mutant in which it was first identified [1]. This sequence motif represents one beta-sheet blade, and several of these repeats can associate to form a beta-propeller. For instance, the motif appears 6 times in Drosophila egg-chamber regulatory protein, creating a 6-bladed beta-propeller. The motif is also found in mouse protein MIPP [2] and in a number of poxviruses. In addition, kelch repeats have been recognised in alpha- and beta-scruin [2, 3], and in galactose oxidase from the fungus Dactylium dendroides [4, 5]. The structure of galactose oxidase reveals that the repeated sequence corresponds to a 4-stranded anti-parallel beta-sheet motif that forms the repeat unit in a super-barrel structural fold [6].

The known functions of kelch-containing proteins are diverse: scruin is an actin cross-linking protein; galactose oxidase catalyses the oxidation of the hydroxyl group at the C6 position in D-galactose; neuraminidase hydrolyses sialic acid residues from glycoproteins; and kelch may have a cytoskeletal function, as it is localised to the actin-rich ring canals that connect the 15 nurse cells to the developing oocyte in Drosophila [7]. Nevertheless, based on the location of the kelch pattern in the catalytic unit in galactose oxidase, functionally important residues have been predicted in glyoxal oxidase [7].

This entry represents the 6-bladed Kelch beta-propeller, which consists of six 4-stranded beta-sheet motifs (or six Kelch repeats).

1. kelch encodes a component of intercellular bridges in Drosophila egg chambers. Cell 72, 681-93
2. beta-Scruin, a homologue of the actin crosslinking protein scruin, is localized to the acrosomal vesicle of Limulus sperm. J. Cell. Sci. 108 ( Pt 10), 3155-62
3. Sequence and domain organization of scruin, an actin-cross-linking protein in the acrosomal process of Limulus sperm. J. Cell Biol. 128, 51-60
4. Drosophila kelch motif is derived from a common enzyme fold. J. Mol. Biol. 236, 1277-82
5. Novel thioether bond revealed by a 1.7 A crystal structure of galactose oxidase. Nature 350, 87-90
6. Crystal structure of a free radical enzyme, galactose oxidase. J. Mol. Biol. 238, 794-814

Kelch is a 50-residue motif, named after the Drosophila mutant in which it was first identified [
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