High Yield Preparation of Functionally Active Catalytic-Translocation Domain Module of Botulinum Neurotoxin Type A That Exhibits Uniquely Different Enzyme Kinetics

Abstract

Botulinum neurotoxins (BoNTs) are the most toxic proteins known to cause flaccid muscle paralysis as a result of inhibition of neurotransmitter release from peripheral cholinergic synapses. BoNT type A (BoNT/A) is a 150 kDa protein consisting of two major subunits: light chain and heavy chain. The light chain is required for the catalytic activity of neurotoxin, whereas the C and N terminal domains of the heavy chain are required for cell binding, and translocation of light chain across the endosome membranes, respectively. To better understand the structural and functional aspects of BoNT/A intoxication we report here the development of high yield Escherichia coli expression system (2 to 20-fold higher yield than the value reported in the literature) for the production of recombinant light chain-translocation domain (rLC-TD/A) module of BoNT/A which is catalytically active and translocation competent. The open reading frame of rLC-TD/A was PCR amplified from deactivated recombinant BoNT/A gene (a non-select agent reagent), and was cloned using pET45b (+) vector to express in Escherichia coli cells. The purification procedure included a sequential order of affinity chromatography, trypsinization, and anion exchange column chromatography. We were able to purify >95 % pure, catalytically active and structurally well-folded protein. Comparison of enzyme kinetics of purified LC-TD/A to full-length toxin and rLC/A (recombinant light chain A) suggest that the affinity for the substrate is in between endopeptidase domain and botulinum toxin. The potential application of the purified protein has been discussed in toxicity and translocation assays.