title: Probing BoNT/A protease exosites: implications for inhibitor design and light chain longevity.
abstract: Botulinum neurotoxin serotype A (BoNT/A) is one of the most lethal toxins known. Its extreme toxicity is due to its light chain (LC), a zinc protease that cleaves SNAP-25, a synaptosome-associated protein, leading to the inhibition of neuronal activity. Studies on BoNT/A LC have revealed that two regions, termed exosites, can play an important role in BoNT catalytic activity. A clear understanding of how these exosites influence neurotoxin catalytic activity would provide a critical framework for deciphering the mechanism of SNAP-25 cleavage and the design of inhibitors. Herein, based on the crystallographic structure of BoNT/A LC complexed with its substrate, we designed an α-exosite binding probe. Experiments with this unique probe demonstrated that α-exosite binding enhanced both catalytic activity and stability of the LC. These data help delineate why α-exosite binding is needed for SNAP-25 cleavage and also provide new insights into the extended lifetime observed for BoNT/A LC in vivo.
authors.affiliation: Departments of Chemistry and Immunology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States.
authors.forename: Song
authors.initials: S
authors.lastname: Xue
authors.forename: Sacha
authors.initials: S
authors.lastname: Javor
authors.forename: Mark S
authors.initials: MS
authors.lastname: Hixon
authors.forename: Kim D
authors.initials: KD
authors.lastname: Janda
mesh_terms: D001665:Binding Sites; D019274:Botulinum Toxins, Type A / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D015195:Drug Design; D006801:Humans; D011480:Protease Inhibitors / Q000737:chemistry*; D050825:Synaptosomal-Associated Protein 25 / Q000737:chemistry*
chemical_list: D011480:Protease Inhibitors; C494208:SNAP25 protein, human; D050825:Synaptosomal-Associated Protein 25; D019274:Botulinum Toxins, Type A