Monoclonal antibodies targeting the alpha-exosite of botulinum neurotoxin serotype/a inhibit catalytic activity

Yongfeng Fan, Isin N. Geren, Jianbo Dong, Jianlong Lou, Weihua Wen, Fraser Conrad, Theresa J. Smith, Leonard A. Smith, Mengfei Ho, Melissa Pires-Alves, Brenda A. Wilson, James D. Marks

Research output: Contribution to journalArticlepeer-review


The paralytic disease botulism is caused by botulinum neurotoxins (BoNT),multi-domain proteins containing a zinc endopeptidase that cleaves the cognate SNARE protein, thereby blocking acetylcholine neurotransmitter release. Antitoxins currently used to treat botulism neutralize circulating BoNT but cannot enter, bind to or neutralize BoNT that has already entered the neuron. The light chain endopeptidase domain (LC) of BoNT serotype A (BoNT/A) was targeted for generation ofmonoclonal antibodies (mAbs) that could reverse paralysis resulting from intoxication by BoNT/A. Single-chain variable fragment (scFv) libraries from immunized humans and mice were displayed on the surface of yeast, and 19 BoNT/A LC-specific mAbs were isolated by using fluorescence-activated cell sorting (FACS). Affinities of the mAbs for BoNT/A LC ranged from a KD value of 9.0×10-11 M to 3.53×10-8 M(mean KD 5.38×10-9 M and median KD 1.53×10-9 M), as determined by flow cytometry analysis. Eleven mAbs inhibited BoNT/A LC catalytic activity with IC50 values ranging from 8.3 ~73×10-9M. The fine epitopes of selected mAbs were also mapped by alanine-scanning mutagenesis, revealing that the inhibitory mAbs bound the α-exosite region remote from the BoNT/A LC catalytic center. The results provide mAbs that could prove useful for intracellular reversal of paralysis postintoxication and further define epitopes that could be targeted by small molecule inhibitors.

Original languageEnglish (US)
Article numbere0135306
JournalPloS one
Issue number8
StatePublished - Aug 14 2015

ASJC Scopus subject areas

  • General

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