GFP-SNAP25 fluorescence release assay for botulinum neurotoxin protease activity
The present invention provides a nucleic acid molecule which contains a nucleotide sequence encoding a SNAP-25 substrate which includes (i) a green fluorescent protein; (ii) a first partner of an affinity couple; and (iii) a portion of SNAP-25 that includes a BoNT/A, BoNT/C1 or BoNT/E recognition sequence containing a cleavage site, where the cleavage site intervenes between the green fluorescent protein and the first partner of the affinity couple. Further provided herein is a nucleic acid molecule which contains a nucleotide sequence encoding a tagged toxin substrate which includes (i) a fluorescent protein; (ii) a first partner of an affinity couple; and (iii) a clostridial toxin recognition sequence containing a cleavage site, where the cleavage site intervenes between the fluorescent protein and the first partner of the affinity couple.
1. A method of determining clostridial toxin protease activity, comprising the steps of:
(a) treating with a sample, in solution phase under conditions suitable for clostridial toxin protease activity, a tagged toxin substrate comprising
(i) a fluorescent protein;
(ii) a first partner of an affinity couple; and
(iii) a clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent protein and said first partner of the affinity couple, such that a fluorescent cleavage product is generated when clostridial toxin is present in said sample;
(b) contacting said treated sample with a second partner of the affinity couple, thereby forming stable complexes comprising said first and second partners of said affinity couple; and
(c) assaying the presence or amount of said fluorescent cleavage product in said treated sample, thereby determining clostridial toxin protease activity.
2. The method of claim 1 , wherein said fluorescent protein is selected from the group green fluorescent protein (GFP), blue fluorescent protein (BFP), cyan fluorescent protein (CFP), yellow fluorescent protein (YFP) and red fluorescent protein (RFP).
3. The method of claim 1 , wherein said fluorescent protein is GFP.
4. The method of claim 1 , 2 or 3 , wherein said first partner of the affinity couple is selected from the group histidine tag, glutathione-S-transferase, maltose-binding protein, a biotinylation sequence, streptavidin, S peptide, S protein, FLAG, hemagluttinin (HA), c myc and AU1.
5. The method of claim 1 , wherein said first partner of the affinity couple is a histidine tag.
6. The method of claim 1 , wherein said recognition sequence is a botulinum toxin recognition sequence.
7. The method of claim 1 , wherein said substrate is cleaved with an activity of at least 1 nanomole/minute/milligram toxin.
8. The method of claim 1 , wherein said substrate is cleaved with an activity of at least 100 nanomoles/minute/milligram toxin.
9. The method of claim 1 , wherein said substrate is cleaved with an activity of at least 1000 nanomoles/minute/milligram toxin.
10. The method of claim 1 , wherein said second partner of the affinity couple is immobilized.
11. The method of claim 1 or 10 , wherein said second partner of the affinity couple comprises cobalt (Co2+).
12. The method of claim 1 or 10 , wherein said second partner of the affinity couple comprises nickel (Ni2+).
13. The method of claim 1 , further comprising separating said fluorescent cleavage product from said stable complexes prior to step (c).
14. The method of claim 13 , wherein said separating comprises applying said treated sample to a column, wherein said second partner of the affinity couple is immobilized on said column.
15. The method of claim 13 , wherein said separating comprises applying said treated sample to a filter plate, wherein said second partner of the affinity couple is immobilized on said filter plate.
16. The method of claim 1 , further comprising step (d) assaying the amount of uncleaved tagged toxin substrate in said treated sample.
17. The method of claim 1 , wherein said sample is isolated clostridial toxin.
18. The method of claim 1 , wherein said sample is isolated clostridial light chain.
19. The method of claim 1 , wherein said sample is a formulated clostridial toxin product.
20. The method of claim 19 , wherein said formulated product is a formulated BoNT/A product.
21. The method of claim 1 , wherein said sample is a whole or partially purified cellular extract containing recombinantly expressed clostridial toxin.