Patent ID: 7374896

Claim:
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.