An Expanded Set of Amino Acid Analogs for the Ribosomal Translation of Unnatural Peptides

BACKGROUND: The application of in vitro translation to the synthesis of unnatural peptides may allow the production of extremely large libraries of highly modified peptides, which are a potential source of lead compounds in the search for new pharmaceutical agents. The specificity of the translation apparatus, however, limits the diversity of unnatural amino acids that can be incorporated into peptides by ribosomal translation. We have previously shown that over 90 unnatural amino acids can be enzymatically loaded onto tRNA. METHODOLOGY/PRINCIPAL FINDINGS: We have now used a competition assay to assess the efficiency of tRNA-aminoacylation of these analogs. We have also used a series of peptide translation assays to measure the efficiency with which these analogs are incorporated into peptides. The translation apparatus tolerates most side chain derivatives, a few alpha,alpha disubstituted, N-methyl and alpha-hydroxy derivatives, but no beta-amino acids. We show that over 50 unnatural amino acids can be incorporated into peptides by ribosomal translation. Using a set of analogs that are efficiently charged and translated we were able to prepare individual peptides containing up to 13 different unnatural amino acids. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that a diverse array of unnatural building blocks can be translationally incorporated into peptides. These building blocks provide new opportunities for in vitro selections with highly modified drug-like peptides

A tRNA aminoacylation system for non-natural amino acids based on a programmable ribozyme

The ability to recognize tRNA identities is essential to the function of the genetic coding system. In translation aminoacyl-tRNA synthetases (ARSs) recognize the identities of tRNAs and charge them with their cognate amino acids. We show that an in vitro−evolved ribozyme can also discriminate between specific tRNAs, and can transfer amino acids to the 3' ends of cognate tRNAs. The ribozyme interacts with both the CCA-3' terminus and the anticodon loop of tRNAfMet, and its tRNA specificity is controlled by these interactions. This feature allows us to program the selectivity of the ribozyme toward specific tRNAs, and therefore to tailor effective aminoacyl-transfer catalysts. This method potentially provides a means of generating aminoacyl tRNAs that are charged with non-natural amino acids, which could be incorporated into proteins through cell-free translation

Deskilling, agrodiversity, and the seed trade: a view from contemporary British allotments

Over the last half-century, quality control standards have had the perverse effect of restricting the circulation of non-commercially bred vegetable cultivars in Britain. Recent European and British legislation attempts to compensate for this loss of agrodiversity by relaxing genetic purity standards and the cost of seed marketing for designated ‘‘Amateur’’ and ‘‘Conservation’’ varieties. Drawing on fieldwork conducted at a British allotment site, this article cautions against bringing genetically heterogeneous cultivars into the commercial sphere. Such a move may intensify the horticultural ‘‘deskilling’’ of British allotment gardeners, who have come to rely on commercial seed catalogs as sources of germplasm and knowledge. Horticultural deskilling also entails the delegation of seed selection activities to professional breeders and the potential loss of agrodiversity. The activities of dedicated seed savers who save and circulate the seed of genetically heterogeneous ‘‘heritage’’ varieties, in a manner similar to the management of landraces in the global South, may provide a better model for attempts to safeguard vegetable diversity in the global North