Luminescence resonance energy transfer (LRET) assays for clostridial toxin activity
Clostridial toxin substrates comprising a lanthanide donor complex, an acceptor, and a Clostridial toxin recognition sequence including a cleavage site; methods for determining the activity of a Clostridial toxin from a test sample using such Clostridial toxin substrates; cell compositions comprising such Clostridial toxin substrates and a Clostridial toxin receptor; and methods for determining the activity of a Clostridial toxin from a test sample using such cell compositions.
1. A cell composition comprising:
a. a Clostridial toxin substrate comprising
i. a lanthanide donor complex comprising a lanthanide binding site and a lanthanide ion;
ii. an acceptor;
iii. a Clostridial toxin recognition sequence including a P 1 -P 1 ′ cleavage site that intervenes between the lanthanide donor complex and the acceptor; and
iv. a membrane targeting domain;
wherein the acceptor has an absorbance spectrum overlapping the emission spectrum of the lanthanide donor complex; and
wherein, under the appropriate conditions, resonance energy transfer is exhibited between the lanthanide donor complex and the acceptor; and
b. a Clostridial toxin receptor capable of initiating the intoxication process by selectively binding a Clostridial toxin.
2. The composition according to 1 , wherein the Clostridial toxin receptor comprises an endogenous Clostridial toxin receptor.
3. The composition according to 1 , wherein the Clostridial toxin receptor comprises an exogenous Clostridial toxin receptor.
4. The composition according to 1 , wherein the cell is a neuronal cell.
5. The composition according to 1 , wherein the cell is a non-neuronal cell.
6. The substrate according to claim 1 , wherein the lanthanide binding site has a Kd for a lanthanide ion of less than 1 μM.
7. The composition according to claim 1 , wherein the lanthanide binding site comprises a chelate, a cryptate, or an EF-hand motif.
8. The composition according to claim 1 , wherein the acceptor is an acceptor fluorophore.
9. The composition according to claim 8 , wherein the acceptor fluorophore comprises a fluorescent protein, a fluorophore binding protein, or a fluorescent dye.
10. The composition according to claim 1 , wherein the acceptor is a non fluorescent acceptor.
11. The composition according to claim 1 , wherein the lanthanide donor complex further comprises an antenna.
12. The composition according to claim 11 , wherein the antenna is distinct from the lanthanide-binding site.
13. The composition according to claim 11 , wherein the antenna is incorporated with lanthanide biding site.
14. The composition according to claim 1 , wherein the substrate is a peptide having a length of at most 20 residues, at most 50 residues, at most 100 residues, or at most 150 residues.
15. The composition according to claim 1 , wherein the substrate is a peptide having a length of at least 100 residues, at least 300 residues, at least 500 residues, or at least 700 residues.
16. The composition according to claim 1 , wherein the Clostridial toxin recognition sequence is a peptide having a length of at most 20 residues, at most 30 residues, at most 40 residues or at most 50 residues.
17. The composition according to claim 1 , wherein the Clostridial toxin recognition sequence is a peptide having a length of at least 20 residues, at least 50 residues, at least 100 residues, or at least 200 residues.
18. The composition according to claim 1 , wherein the substrate can be cleaved with an activity of at least 1 nanomole/minute/milligram toxin, at least 20 nanomoles/minute/milligram toxin or at least 100 nanomoles/minute/milligram toxin.