Evolution steps back

Sometimes a step back is needed before going forward. Merridee Wouters, Ke Liu, Peter Riek, and Ahsan Husain (Victor Chang Cardiac Research Institute, Sydney, Australia) find that uniquely specialized serine proteases evolved in two steps: an ancestor protease first became more promiscuous and despecialized before its duplicated progeny were then respecialized.

Serine proteases found in vertebrates today come in various flavors: trypsin-like enzymes cleave after basic residues, but nontrypsin-like proteases favor nonbasic residues. Husain's group used phylogenetic inference to predict the structure of ancient serine proteases. They find that, although the most ancient proteases were specialized with trypsin-like qualities, the increased diversity that later spawned nontrypsin-like qualities was achieved by recreating a less specialized intermediate.

An in vitro–produced enzyme based on the predicted sequence of this less specialized ancestor did indeed have...