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Meet the 'tadpole': a new breed of DNA-protein hybrid
Dec 23, 2004, 22:35, Reviewed by: Dr.
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By Sanjukta, Medical Correspondent,
Researchers hungry for an adaptable system for the high-sensitivity quantification of biomolecules may have found the answer in� tadpoles?
Considering the sensitivity and versatility of Polymerase Chain Reaction (PCR)-based applications, biologists can perhaps be forgiven for becoming a bit spoiled, and demanding the same ease and level of sensitivity for the detection of non-nucleic acid-based molecules. However, a powerful new tool described in the January issue of Nature Methods promises just such sensitivity for the detection of a versatile range of targets, including proteins and small-molecule compounds.
Meet the 'tadpole': a new breed of DNA-protein hybrid developed by Ian Burbulis, Roger Brent, and their colleagues at the Molecular Sciences Institute (Berkeley, CA). The tadpole 'head' consists of a protein element, such as an antibody, with targeted affinity for a specific molecule, while the 'tail' is a unique DNA tag that enables PCR-based quantification. The two halves are synthesized separately, then neatly joined via a naturally occurring splicing reaction to generate the ready-to-use tadpole.
After adding the tadpoles to a sample, the amount of tag sequence amplified by PCR reveals the quantity of tadpole-bound target with surprising accuracy. Burbulis et al. began with a tadpole targeted against the vitamin biotin, and found that they could detect as few as 600 molecules with 95% confidence, and that their tadpoles offered a limit of detection 109 lower than ELISA, a commonly used antibody-based diagnostic assay. They achieved equally sensitive detection using different kinds of 'head' molecules to quantify targets such as anthrax toxin, consistently surpassing the limits of ELISA.
In an accompanying News & Views feature, Stanford researcher Garry Nolan assesses the tadpole, and concludes that the simplicity, adaptability, and sensitivity of this approach "make this an appealing system for researchers wanting a standardized, high-throughput, and accurate detection system for... just about anything."
Leukotrienes are produced by the enzyme 5-lipoxygenase (5-LO). In the new study, Colin Funk and his colleagues show that cells expressing 5-LO are an important component of aortic aneurysms in mice. They also found that reducing 5-LO expression markedly attenuates the formation of aneurysms. This effect seems to depend on the regulation of inflammatory proteins: the leukotriene LTD4 stimulates the production of proinflammatory molecules, and the absence of 5-LO correlates with their reduced expression.
These data link 5-LO pathway to inflammation of the arterial wall and to pathogenesis of aortic aneurysms, identifying a potential therapeutic target for pharmacological intervention. 
- Nature Methods
January 2005 issue of Nature Methods
The researchers used their technique in mice lacking the protein dystrophin, which have a pathology that resembles Duchenne muscular dystrophy. Intravenous delivery of the dystrophin gene to the skeletal muscles of these mice alleviated the disease and improved muscular function, highlighting the therapeutic potential of the method.
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