Patent ID: 8455203

Claim:
A method of detecting the activity of retargeted endopeptidase in a sample, wherein the retargeted endopeptidase comprises an enzymatic domain, comprising a) contacting a cell with a sample suspected of comprising retargeted endopeptidase; wherein the cell is from an established cell line expressing a SNAP-25 polypeptide consisting essentially of at least a portion of human SNAP-25 comprising SEQ ID NO: 5 cleavable by the enzymatic domain; wherein the established cell line is susceptible to intoxication by the retargeted endopeptidase at about or less than 50 nmol per liter culture medium, as indicated by the enzymatic cleavage of the SNAP-25 polypeptide by the enzymatic domain to yield a fragment of said SNAP25 polypeptide comprising the C-terminal amino acid sequence of SEQ ID NO: 38; b. isolating polypeptides from the cell; c. contacting the polypeptides with a monoclonal antibody that specifically binds to the peptide of SEQ ID NO: 38; wherein said antibody specifically binds to an epitope of said fragment of said SNAP25 polypeptide comprising the C-terminal amino acid sequence of SEQ ID NO: 38 with an equilibrium disassociation constant of less than 0.450 nM and wherein said antibody has an association rate constant for an epitope of intact SNAP-25 polypeptide comprising SEQ ID NO: 5 of less than 1×10 1 M −1 s −1 ; and, d. detecting the presence of any antibody-antigen complex comprising the antibody and the fragment of said SNAP-25 polypeptide comprising the C-terminal amino acid sequence of SEQ ID NO: 38; wherein a higher amount of the antibody-antigen complex detected correlates to a higher amount of activity of the retargeted endopeptidase in the sample.