Patent ID: 8053208

Claim:
A Clostridial toxin substrate, comprising: a) a donor fluorophore; b) an acceptor having an absorbance spectrum overlapping the emission spectrum of said donor fluorophore; and c) a Clostridial toxin recognition sequence comprising a Clostridial toxin P5-P4-P3-P2-P1-P1′-P2′-P3′-P4′-P5′ cleavage site sequence, said Clostridial toxin P5-P4-P3-P2-P1-P1′-P2′-P3′-P4′-P5′ cleavage site sequence intervening between said donor fluorophore and said acceptor; wherein said donor fluorophore, said acceptor, or both said donor fluorophore and said acceptor is not positioned within said Clostridial toxin P5-P4-P3-P2-P1-P1′-P2′-P3′-P4′-P5′ cleavage site sequence; and wherein, under the appropriate conditions, resonance energy transfer is exhibited between said donor fluorophore and said acceptor.