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Biochemists have introduced two new amino acids into a single E. coli protein. Previously it had only been possible to introduce a single new amino acid into a protein. The discovery means that bacteria could soon be genetically engineered to produce proteins that have been modified with various characteristics of interest for researchers, says Wenshe Liu, assistant professor of chemistry at Texas A&M University.  (Credit: iStockphoto)

TEXAS A& M (US)—For the first time researchers have successfully incorporated two different noncanonical amino acids into a single protein in E. coli bacteria.

The discovery means that bacteria could soon be genetically engineered to produce proteins that have been modified with various characteristics of interest for researchers, says Wenshe Liu, assistant professor of chemistry at Texas A&M University.

E. coli, commonly found in the lower intestine of warm-blooded organisms, encompasses many strains, most of which are harmless. However, some strains cause serious food poisoning in humans and are occasionally responsible for costly product recalls.

Previously it had only been possible to introduce a single new amino acid into a protein, the genetic code of which includes information for only 20 amino acids, says Liu. Details of the research are published in the journal Angewandte Chemie.

“All proteins are made up of 20 amino acids which are genetically coded,” Liu says. “The work we have done was to devise a method to significantly expand the amino acid inventory of proteins and synthesize proteins made up of 22 different kinds of amino acids.”

In normal protein synthesis, tRNA transports the amino acid to the place where protein synthesis occurs at the best of codons that signal when to start and stop, he explains.

Three “stop codons” naturally exist to code protein translation termination. By mutating two unique tRNAs to recognize two different stop codons, mutations in their associated aminoacyl tRNA synthetases occur that allow for the introduction of two synthetic amino acids to the tRNAs.

Liu and his colleagues then incorporated the altered genetic material into the bacterial cells, which then assimilate two noncanonical amino acids into one protein.

“This work has far-reaching potential with applications in basic research, medicine, and industry,” Liu explains.

The study was funded in part by the Texas A&M Department of Chemistry and a grant from the Houston-based Welch Foundation.

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