CRYSTAL-STRUCTURE OF A HEDGEHOG AUTOPROCESSING DOMAIN - HOMOLOGY BETWEEN HEDGEHOG AND SELF-SPLICING PROTEINS

The similar to 25 kDa carboxy-terminal domain of Drosophila Hedgehog p rotein (Hh-C) possesses an autoprocessing activity that results in an intramolecular cleavage of full-length Hedgehog protein and covalent a ttachment of a cholesterol moiety to the newly generated amino-termina l fragment. We have identified a 17 kDa fragment of Hh-C (Hh-C-17) act ive in the initiation of autoprocessing and report here its crystal st ructure. The Hh-C-17 structure comprises two homologous subdomains tha t appear to have arisen from tandem duplication of a primordial gene. Residues in the Hh-C-17 active site have been identified, and their ro le in Hedgehog autoprocessing probed by site-directed mutagenesis. Asp ects of sequence, structure, and reaction mechanism are conserved betw een Hh-C-17 and the self-splicing regions of inteins, permitting recon struction of a plausible evolutionary history of Hh-C and the inteins.