Serine? So last century. Valine? Over it. Glycine? You’ve got to be kidding me.
Those chemicals are part of the 20 amino acids that are typically incorporated into proteins. That means they have a dedicated place in what’s called the genetic code, which translates between the bases of DNA to the amino acids of proteins.
Granted, the genetic code has enabled the entire diversity and complexity of life on Earth, from E. coli to T. rex. But still, researchers are starting to find this kind of limiting. Life has evolved ways of using more than 140 amino acids in proteins; and once we start tinkering with the things, we can make scads more. Just because evolution has done so doesn’t mean we need to rely on only these 20 old boring ones. What follows is a look at how and why we want to engineer artificial amino acids into cells and living organisms.
Transfer RNAs (tRNAs) act as the bridge between DNA and amino acids—the DNA-based directions for how to make a protein and the protein itself. Each set of three bases in DNA can designate one of the 20 canonical amino acids. The tRNAs “read” this genetic triplet and deliver the designated amino acid onto the growing protein. So in order to add a new, artificial amino acid to proteins, researchers have had to engineer—or in some rare cases, find in microbes—a tRNA molecule that will put it into proteins when presented with a specific DNA code.
Usually, the DNA triplet used is not one that already designates an amino acid. Rather, it is one that signals the cell to stop adding amino acids to a protein. Most organisms have three of these stop codes and, with a bit of engineering, can get by with two. Scientists can then put this stop sequence into the middle of genes along with a tRNA that responds to it. When the gene is translated into protein, the tRNA will add an artificial amino acid into the elongating protein chain. Of course, the scientists…