Protein Building Blocks and the Expansion of the Genetic Code
The proteins of all known organisms are built of a set of 20 canonical amino acids prescribed by the genetic code. Many more amino acids occur in nature but they are excluded from ribosomal translation. Nevertheless, nature exploits their vast chemical diversity for the production of highly bioactive peptides by non-ribosomal biosynthesis routes. The extraordinarily rich structural and functional repertoire of the noncanonical amino acids holds great promise for the future of protein engineering, yet we have only just begun to tap the cornucopia of noncanonical building blocks for the biosynthesis of synthetic proteins.
This chapter provides a broad overview of canonical as well as noncanonical amino acids as building blocks for proteins and peptides. It recapitulates the genetic code and its natural deviations. The structures of selected naturally occurring noncanonical amino acids are listed referencing their source and biosynthesis pathways where known. The principles of current approaches to engineer and expand the genetic code are described. Numerous examples illustrate their application in protein engineering, and they are complemented by a compilation of the noncanonical building blocks involved.
KeywordsGenetic Code Chloramphenicol Acetyl Transferase SECIS Element Standard Genetic Code Sense Codon
Bioorthogonal noncanonical amino acid tagging
Canonical amino acid
Conjugative assembly genome engineering
Cyan fluorescent protein
Copper(I)-catalyzed azide–alkyne cycloaddition
Fluorescent noncanonical amino acid tagging
Green fluorescent protein
Inverse electron-demand Diels–Alder reaction
Multiplex automated genome engineering
Orthogonal PylRS/tRNACUA Pyl pair from Methanosarcina mazei
Noncanonical amino acid
ncAA-specific aminoacyl-tRNA synthetase
Non-ribosomal peptide synthesis
Polyfluorinated amino acid
Sense codon recoding
Stop codon suppression
Strain-promoted Huisgen 1,3-dipolar cycloadditions between azides and cyclooctynes
This work has been supported by the Federal Ministry of Science, Research and Economy (BMWFW); the Federal Ministry of Traffic, Innovation and Technology (bmvit); the Styrian Business Promotion Agency SFG; the Standortagentur Tirol; the government of Lower Austria; and ZIT—Technology Agency of the City of Vienna through the COMET Funding Program managed by the Austrian Research Promotion Agency FFG.
I am grateful for support by CHEM21 in the frame of the Innovative Medicines Initiative Joint Undertaking under grant agreement n°115360, resources of which are composed of financial contribution from the European Union’s Seventh Framework Programme (FP7/2007–2013) and EFPIA companies’ in-kind contribution.
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