Duplication, divergence and formation of novel protein topologies.

The rearrangement or permutation of protein substructures is an important mode of divergence. Recent work(1) explored one possible underlying mechanism called permutation-by-duplication, which produces special forms of motif rearrangements called circular permutations. Permutation-by-duplication, involving gene duplication, fusion and truncation, can produce fully functional intermediate proteins(1) and thus represents a feasible mechanism of protein evolution. In spite of this, circular permutations are relatively rare and we discuss possible reasons for their existence.