Structural analysis shows five glycohydrolase families diverged from a common ancestor

Abstract

We have solved the X-ray structure of barley chitinase and bacterial chitosanase. Structural constraints predicted these would work by an inverting mechanism, which has been confirmed biochemically. The two enzymes were compared with lysozymes from goose (GEWL), phage (T4L), and hen (HEWL). Although the proteins share no significant amino acid similarities, they are shown to have a structurally invariant core containing two helices and a three-stranded β sheet that form the substrate binding and catalytic cleft. These enzymes represent a superfamily of hydrolases arising from the divergent evolution of an ancient protein. The glycohydrolase superfamily can be structurally divided into a bacterial family (chitosanase and T4L), and a eucaryotic family represented by chitinase, GEWL, and HEWL. Both families contain the ancestral core but differ at the amino and carboxy termini. The eucaryotes have a small N terminal domain, while the procaryotes have none. The C terminal domain of the eucaryotic family contains a single α-helix, while the prokaryotic domain has three antiparallel helices. J. Exp. Zool. 282:127–132, 1998. © 1998 Wiley-Liss, Inc.