Chemical Bypass Of General Base Catalysis In Hedgehog Protein Cholesterolysis Using A Hyper-Nucleophilic Substrate

Proteins in the hedgehog family undergo self-catalyzed endoproteolysis involving nucleophilic attack by a molecule of cholesterol. Recently, a conserved aspartate residue (D303, or D46) of hedgehog was identified as the general base that activates cholesterol during this unusual autoprocesing event; mutation of the catalyzing functional group (D303A) reduces activity by >10(4)-fold. Here we report near total rescue of this ostensibly dead general base mutant by a synthetic subtrate, 3 beta-hydroperoxycholestang (3HPC) in which the sterol -OH group is replaced by the hyper nucleophilic -OOH group. Other hedgehog point mutants at D303, also unreactive with cholesterol, accepted 3HPC as a substrate with the rank order: WT > D303A approximate to D303N >> D303R, D303E. We attribute the revived activity with 3-HPC to the alpha-effect, where tandem electronegative atoms exhibit exceptionally high nucleophilicity despite relatively low basicity.