Non-FRET botulinum assay
A composition includes an artificial construct having (a) a reporter-containing portion chemically coupled to (b) a cleavage site. The cleavage site interacts with an investigational substance in a manner that cleaves the reporter-containing portion from a remainder of the construct. The cleaved portion is destroyed or otherwise degraded by the local environment, and presence of an investigational substance is evidenced by reduction in signal from the reporter. The investigational substance is preferably a Botulinum toxin (BoTN), and the cleavage sequence is all or part of a SNARE protein. The cleavable reporter-containing portion is preferably Yellow Fluorescent Protein (YFP), Citrine, Venus, or a YPet protein.
1. A method for the qualitative and quantitative detection of a Botulinum toxin, comprising in sequence:
(i) providing a composition that includes an artificial construct and an enzyme,
wherein the construct has (a) a reporter-containing portion comprising a first fluorophore that is degraded by the enzyme, (b) a cleavage site comprising at least a portion of a motif selected from the group consisting of SNAP-25, synaptobrevin, and syntaxin, wherein the motif interacts with a portion of the Botulinum toxin in a manner that produces a cleavage of the first fluorophore from a remainder of the construct, and (c) a second portion comprising a second fluorophore, wherein the cleavage site is interposed between the reporter containing portion and the second portion;
(ii) obtaining a baseline signal emission measurement from the construct;
(iii) exposing the Botulinum toxin composition to the composition; and
(iv) obtaining a further emission measurement from the reporter fluorophore,
wherein the reporter-containing portion and the second portion are positioned in the construct such that FRET emission from the first fluorophore does not show a decreasing trend relative to increasing concentrations of the Botulinum toxin composition, and wherein a normalization emission measurement is obtained from the second fluorophore.
2. The method of claim 1 wherein the first fluorophore comprises Yellow Fluorescent Protein (YFP).
3. The method of claim 1 wherein the first fluorophore is selected from the group consisting of Yellow Fluorescent Protein (YFP), Citrine, Venus, and a YPet protein.
4. The method of claim 1 wherein the first fluorophore is a derivative of at least one of Yellow Fluorescent Protein (YFP), Citrine, Venus, and a YPet protein.
5. The method of claim 1 wherein the second fluorophore is at an opposite end of the construct from the reporter-containing portion.
6. The method of claim 1 wherein the first fluorophore comprises Yellow Fluorescent Protein (YFP), and second fluorophore comprises Cyan Fluorescent Protein (CFP).
7. The method of claim 1 6 wherein the first fluorophore comprises at least one of Yellow Fluorescent Protein (YFP), Citrine, Venus, and a YPet protein, and the second fluorophore comprises at least one of CFP, mStrawberry, and mCherry.
8. The method of claim 1 wherein the first fluorophore comprises a chromophore.
9. The method of claim 1 wherein the construct is produced endogenously by a living transfected cell.
10. The method of claim 1 wherein the composition is contained in a living transfected cell, the first fluorophore comprises at least one of Yellow Fluorescent Protein (YFP), Citrine, Venus, and a YPet protein, and wherein the second fluorophore comprises a second fluorescent protein.
11. The method according to any one of the preceding claims, wherein the baseline emission measurements of step (ii) are obtained by directly exciting the second fluorophore.
12. The method of claim 1 , wherein a measurement of first fluorophore degradation is obtained by collecting emissions of directly, separately excited first fluorophore and second fluorophore.
13. The method of claim 9 , wherein the fluorescent emission of the second fluorophore is used to correct for variations in-cell density and reporter expression in the individual cells.
14. An assay for testing presence of an investigative substance, comprising a cell having an artificial construct and an enzyme, wherein the construct has a protected portion and a protecting portion, selected such that the protected portion includes a first reporter and the protecting portion includes a second reporter, and the investigative substance acts to de-protect the protected portion in vitro, wherein the enzyme facilitates degradation of the protected portion, thereby reducing a signal obtainable from the first reporter, which is used for the quantitative determination of the investigative substance, wherein the first reporter and the second reporter are positioned such that FRET emission from the first reporter does not show a decreasing trend relative to increasing concentrations of the investigative substance and wherein a normalization emission measurement is obtained from the second reporter.
15. The assay of claim 14 , wherein the first reporter comprises a fluorophore preferably being at least one of Yellow Fluorescent Protein (YFP), Citrine, Venus, and a YPet protein, and a cleavage site comprising at least a portion of a motif selected from the group consisting of SNAP-25, synaptobrevin, and syntaxin, wherein the motif interacts with a portion of the Botulinum toxin in a manner that produces a cleavage of at least a portion of the protected portion from a remainder of the construct.
16. The assay of claim 15 , wherein the second reporter is selected from the group comprising CFP, mStrawberry, and mCherry.
17. The assay of claim 15 , wherein the construct contains a membrane-localizing domain, and the enzyme exists in the cytosol of the cell.
18. The assay of claim 1 , wherein the second fluorophore provides the baseline emission, and wherein said baseline emission is used for normalization of the emission measurement from the first fluorophore.
19. The assay of claim 14 , wherein the protecting portion provides a baseline emission, and wherein said baseline emission is used for normalization of a further emission from the protected portion.