Unnatural selection
Chemists build proteins with parts not in the typical toolkit
By Laura Beil
Amino acids are the Legos of life — tiny bricks that snap together, forming the proteins on which every function of life depends. With rare exceptions, cells choose from just 20 kinds of Legos. But this is enough for human cells to assemble the more than 1 million proteins they need to function.
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A couple of decades ago, a few scientists decided that they wanted to play with more Legos. It began as an exercise in academic curiosity, a way to ask some of the Big Questions about life: Why just 20 amino acids? Why those 20? The researchers began to build artificial amino acids in the laboratory — just to see what cells would do with new construction material, and where the exploration would lead.
Today, scientists have created more than 70 of these “unnatural amino acids” and are using them to reboot the protein-making machinery of bacteria, yeast and even mammal cells — all of which seem to welcome extra choice in their protein assembly. Given the success so far, at least two U.S. biotech companies are now using unnatural amino acids to mass-produce proteins previously unknown in nature, aiming to make new drugs that may one day treat cancer, multiple sclerosis or other diseases.