Drosophila kelch motif is derived from a common enzyme fold

A systematic screening of sequence databases with a motif hitherto found only in animal and poxvirus proteins has revealed a trail leading back to prokaryotes. Fortuitously, an X-ray structure is available for one of the identified sequences and shows the fundamental fold to be a set of circularly arranged beta sheets. This structure may be very widely distributed throughout the biological world in sialidases and some other enzymes. In bacteria, a mobile noncatalytic domain is often associated with these same enzymes.