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September 27, 2012
EMBL Chemical Biology: Unnatural Amino Acid Labels
Now I'm listening to David Tirrell of Cal Tech, talking about his lab's work on labeling proteins with azidohomoalanine (Aha) as a marker. He's done a good job showing that (if you don't go wild) that replacement of methionine with this amino acid doesn't perturb things very much at all, and there's a recent paper showing how well the technique works (when combined with stable isotope labeling) for analyzing mixtures of low-abundance proteins. You can now buy all the reagents you need to do this.
The Aha can be activated by wild-type Met tRNA synthetase (MetRS), but he's also working with weirder amino acids that require a mutant RS enzyme. This is useful for even finer-grained experiments; the example shown is for monitoring host-pathogen interactions. Using a Yersinia species, he's showing all sorts of complex results, most of which fall into the category of "Must be important, but we don't know what they mean yet". The bacteria inject a number of as-yet-uncharacterized proteins into mammalian cells, for example, and without techniques like these, you'd never find them.
They've gone as far as doing this in whole living nematodes - it looks like this has been disclosed at meetings, but there doesn't appear to be a full paper on this yet.
A nice quote from the talk: "We did a computational search, which didn't help us out very much, but the experiment was great". Words to live by!
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