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C‑Terminus of Botulinum A Protease Has Profound and Unanticipated Kinetic Consequences upon the Catalytic Cleft

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journal contribution
posted on 2013-02-14, 00:00 authored by Peter Šilhár, Matthew A. Lardy, Mark S. Hixon, Charles B. Shoemaker, Joseph T. Barbieri, Anjali K. Struss, Jenny M. Lively, Sacha Javor, Kim D. Janda
Botulinum neurotoxins (BoNTs) are among the most deadly poisons known, though ironically, they also are of great therapeutic utility. A number of research programs have been initiated to discover small molecule inhibitors of BoNTs metalloprotease activity. Many, though not all, of these programs have screened against a truncated and more stable form of the enzyme, that possesses comparable catalytic properties to the full length enzyme. Interestingly, several classes of inhibitors, notably the hydroxamates, display a large shift in potency between the two enzyme forms. In this report we compare the kinetics of active-site, α-exosite and β-exosite inhibitors versus truncated and full length enzyme. Molecular dynamics simulations conducted with the truncated and homology models of the full length BoNT LC/A indicate the flexibility of the C-terminus of the full length enzyme is responsible for the potency shifts of active-site proximally binding inhibitors while distal binding (α-exosite) inhibitors remain equipotent.