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α‐Effect Furnishes a Mechanistic Bypass for General Base Catalysis in Hedgehog Protein Autoprocessing
Author(s) -
Callahan Brian,
Giner Jose L,
Ciulla Daniel,
Jorgenson Michael
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.605.3
Subject(s) - chemistry , hedgehog , nucleophile , stereochemistry , residue (chemistry) , sterol , mutant , mutagenesis , catalysis , biochemistry , cholesterol , gene
Eukaryotic signaling proteins in the “hedgehog” family undergo a rare autoproteolytic maturation reaction involving nucleophilic attack by cholesterol. A recent mutagenesis study indicated that a conserved aspartate residue (D303) of hedgehog functions as an essential general base, activating the 3‐OH group of cholesterol [Xie J, Owen T, Xia K, Callahan B, Wang C. (2016) J Am Chem Soc. 138(34):10806–9.]. Accordingly, autoprocessing of a point mutant (D303A) was reduced by a factor of >10 4 fold. Here we report that this ostensibly dead mutant can catalyze autoprocessing at near wild‐type levels when cholesterol is replaced by a synthetic sterol, 3‐hydroperoxycholestane (3‐HPC), in which the sterol ‐OH is substituted with ‐ OOH. Other hedgehog point mutants at D303 also accepted 3‐HPC as a substrate albeit to varying degrees, with the rank order of activity: D303H>D303A≈D303N>D303R>>D303E. We attribute the remarkable substrate rescue by 3‐HPC to the alpha‐effect, where nucleophilic groups with tandem electronegative atoms exhibit anomalously high reactivity despite relatively low basicity.