Cell-based fluorescence resonance energy transfer (FRET) assays for clostridial toxins

Abstract

The present invention provides a method of determining clostridial toxin activity by (a) contacting with a sample a cell containing a clostridial toxin substrate that includes a donor fluorophore; an acceptor having an absorbance spectrum overlapping the emission spectrum of the donor fluorophore; and a clostridial toxin recognition sequence containing a cleavage site that intervenes between the donor fluorophore and the acceptor, where resonance energy transfer is exhibited between the donor fluorophore and the acceptor under the appropriate conditions; (b) exciting the donor fluorophore; and (c) determining resonance energy transfer of the contacted cell relative to a control cell, where a difference in resonance energy transfer of the contacted cell as compared to the control cell is indicative of clostridial toxin activity.

Description

[0001] This application is a divisional and claims priority pursuant to 35 U.S.C. §120 to U.S. patent application Ser. No. 10 / 261,161, filed Sep. 27, 2002, which is hereby incorporated by reference in its entirety.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates generally to fluorescence resonance energy transfer and protease assays and, more specifically, to cell-based methods for assaying for clostridial toxin activity. [0004] 2. Background Information [0005] The neuroparalytic syndrome of tetanus and the rare but potentially fatal disease, botulism, are caused by neurotoxins produced by bacteria of the genus Clostridium. These clostridial neurotoxins are highly potent and specific poisons of neural cells, with the human lethal dose of the botulinum toxins on the order of nanograms. Thus, the presence of even minute levels of botulinum toxins in foodstuffs represents a public health hazard that must be avoided through rigorous testi...

AI Technical Summary

Benefits of technology

[0022] A variety of means can be used to determine resonance energy transfer in a method of the invention. In one embodiment, a method of the invention includes the step of detecting donor fluorescence intensity of the contacted cell, where increased donor fluorescence intensity of the contacted cell as compared to the control cell is indicative of clostridial toxin activity. In another embodiment, a method of the invention includes the step of detecting acceptor fluorescence intensity of the contacted cell, where decreased acceptor fluorescence intensity of the contacted cell as compared to the control cell is indicative of clostridial toxin activity. In a further embodiment, a method of the invention includes the step of detecting an acceptor emission maximum and a donor fluorophore emission maximum of the contacted cell, where a shift in emission maxima from near the acceptor emission maximum to near the donor fluorophore emission maximum is indicative of clostridial toxin activity. In yet a further embodiment, a method of the invention includes the step of detecting the ratio of fluorescence amplitudes near an acceptor emission maximum to the fluorescence amplitudes near a donor fluorophore emission maximum of the contacted cell, where a decreased ratio in the contacted cell as compared to the control cell is indicative of clostridial toxin activity. In still another embodiment, a method of the invention includes the step of detecting the excited state lifetime of the donor fluorophore in the contacted cell, where an increased donor fluorophore excited state lifetime in the contacted cell as compared to the control cell is indicative of clostridial toxin activity. If desired, the step of determining resonance energy transfer can be repeated at one or more later time intervals. In addition, the conditions suitable for clostridial toxin activity can be selected, if desired, such that the assay is linear.

Problems solved by technology

However, in spite of their potentially deleterious effects, low controlled doses of botulinum neurotoxins have been successfully used as therapeutics and for some cosmetic applications.

Unfortunately, the mouse lethality assay suffers from several drawbacks: cost due to the large numbers of laboratory animals required; lack of specificity; the potential for inaccuracy unless large animal groups are used; and the necessary sacrifice of animal life.

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