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Post-translational mutagenesis for installation of natural and unnatural amino acid side chains into recombinant proteins

Nature Protocols volume 12, pages 22432250 (2017) | Download Citation

Abstract

Methods for installing natural and unnatural amino acids and their modifications into proteins in a benign and precise manner are highly sought-after in protein science. Here we describe a protocol for 'post-translational mutagenesis' that enables the programmed installation of protein side chains through the use of rapid, mild and operationally simple free-radical chemistry performed on recombinantly expressed and purified proteins. By introduction of protein dehydroalanine (Dha) residues (in this instance, from a unique cysteine residue introduced by site-directed mutagenesis) as free-radical trapping 'tags' for downstream modification, exquisite control over the site of subsequent modification is achieved. Using readily available alkyl halide precursors and simple borohydride salts, alkyl radicals can be generated in aqueous solution. These alkyl radicals react rapidly with protein-bound Dha residues to yield functionalized protein products with new carbon–carbon bonds. Once the Dha is installed, the introduction of the desired functionality is limited only by the requirement for polarity matching of the generated radical with the Dha 'acceptor', the solubility of the alkyl halide precursors in aqueous solution and the kinetics of the reaction itself. For example, methylated derivatives of lysine, arginine and glutamine are readily accessible. Furthermore, as the side chains are constructed chemically, many unnatural modifications can also be directly introduced as part of the side chain, including isotope reporters (19F, 13C) that can be used in biophysical experiments such as protein NMR. From a suitable cysteine mutant of the target protein, the entire procedure for this chemical post-translational mutation takes 2 d and is readily performed by nonchemists.

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Acknowledgements

T.H.W. was supported by the Rutherford Foundation. B.G.D. was supported by a Royal Society Wolfson Research Merit Award.

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Affiliations

  1. Department of Chemistry, University of Oxford, Oxford, UK.

    • Tom H Wright
    •  & Benjamin G Davis

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Contributions

B.G.D. and T.H.W. designed the research. T.H.W. performed the experiments. T.H.W. and B.G.D. wrote the paper.

Competing interests

B.G.D. is a member of the Catalent Biologics Scientific Advisory Board. B.G.D. is one of the inventors on patent WO 2009103941, filed by the University of Oxford and assigned to Catalent Biologics. The patent covers, in one claim, reaction of the carbon–carbon double bond of dehydroalanine residues reacted with an organohalide in the presence of elemental zinc. The other authors declare no competing financial interests.

Corresponding author

Correspondence to Benjamin G Davis.

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https://doi.org/10.1038/nprot.2017.087

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