The present invention relates to means and methods for determining neurotoxin activity. Specifically, it relates to a polypeptide having caspase activity comprising a large subunit and a small subunit wherein the caspase further comprises a neurotoxin cleavage site which upon cleavage activates the caspase activity. Also encompassed are polynucleotides encoding the polypeptides as well as vectors or host cells comprising the polynucleotides. The present invention further relates to a method for determining neurotoxin activity in a sample based on the polypeptide of the invention as well as the use of the polypeptide for determining neurotoxin activity in a sample, in general.
