Patent ID: 8013113

Claim:
A botulinum toxin substrate, comprising: a) a donor fluorophore; b) an acceptor having an absorbance spectrum overlapping the emission spectrum of said donor fluorophore, wherein the acceptor is an acceptor fluorophore; and c) a botulinum toxin type B recognition sequence comprising a botulinum toxin type B P5-P4-P3-P2-P1-P1′-P2′-P3′-P4′-P5′ cleavage site sequence, said botulinum toxin type B P5-P4-P3-P2-P1-P1′-P2′-P3′-P4′-P5′ cleavage site sequence intervening between said donor fluorophore and said acceptor; wherein either of said donor fluorophore, said acceptor, or both said donor fluorophore and said acceptor are genetically encoded; and wherein, under the appropriate conditions, resonance energy transfer is exhibited between said donor fluorophore and said acceptor fluorophore.