|Dogs are good at Smelling Things... (I took this picture)|
In 2007, researchers genetically engineered Saccharomyces cerevisiae (beer yeast) to express a rat olfactory receptor. But not just any old fully functioning olfactory receptor. Radhika et al. (2007) made a lovely franken-protein by using bits of dna from all over the place. They basically end up with a dna sequence coding for a receptor that expresses GFP (green fluorescence protein) when it is 'triggered.' The key here is that this 'trigger' could be easily changed.
They first demonstrate that they can replace the trigger part of this receptor, making it sensitive to the scent of vanillin or cintronellal. While yeast that can turn green in response to the relaxing scent of vanilla might make for great advances in home decorating, the authors actually wanted to make a yeast strain that would fluoresce in response to the scent of bombs.
Specifically, they wanted the yeast to respond to DNT, a mimic of TNT. To do this, they had to conduct a large assay on a 'library of cDNA inserts.' That basically means they had to switch in different 'triggers' for the receptor based on known strings of olfactory receptor dna and test each one to see if it responded to DNT. Lucky for them, they happened to find one.
|Radhika et al., 2007 Figure 4A: yeast glows in response to DNT|
And voila! a strain of bomb-sniffing yeast!
While I don't think we'll be replacing bomb-sniffing dogs with petri dishes of glowing yeast any time soon, this is a significant step toward cellular level bomb-detection. More importantly, this study developed a new way to screen dna. They have created a versatile receptor 'cassette' into which they can place a string of dna and test which ligands or odors 'trigger' that section of the protein.
Radhika V, Proikas-Cezanne T, Jayaraman M, Onesime D, Ha JH, & Dhanasekaran DN (2007). Chemical sensing of DNT by engineered olfactory yeast strain. Nature chemical biology, 3 (6), 325-30 PMID: 17486045