A protein functionalization platform based on selective reactions at methionine residues

Abstract

Nature displays a remarkable ability to carry out site-selective post-translational modification of proteins, therefore enabling a dramatic increase in their functional diversity 1 . Inspired by this, chemical tools have evolved for the synthetic manipulation of protein structure and function, and have become essential to the continued advancement of chemical biology, molecular biology and medicine. However, the number of chemical transformations suitable for effective protein functionalization is limited because the stringent demands inherent to biological systems preclude the applicability of many potential processes 2 . Put simply, these chemical transformations often need to be selective at a single site on a protein, proceed with very fast reaction rates, operate under biologically ambient conditions and should provide homogeneous products with near perfect conversion 2 – 7 . While many elegant bioconjugation methods exist at cysteine, lysine and tyrosine, we reasoned that a method targeting a less explored amino acid would significantly expand the protein functionalization toolbox. Herein, we report the development of a multifaceted-approach to protein functionalization based on chemoselective labelling at methionine residues. By exploiting the unique electrophilic reactivity of a bespoke hypervalent iodine reagent, one can target the S -Me group in the side-chain of methionine. The bioconjugation reaction is fast, selective, operates at low µM concentrations and is complementary to existing bioconjugation strategies. Moreover, the new reaction produces a protein conjugate that is, itself, a high energy intermediate with reactive properties that can serve as a platform for the development of secondary, visible-light mediated bioorthogonal protein functionalization processes. Taken together, the merger of these approaches provides a versatile platform for the development of distinct transformations that can deliver versatile, information-rich protein conjugates directly from the native biomacromolecules.

Modifying Methionine on Proteins

“…Recently, Gaunt et al. reported another method of labeling methionine with high‐valent iodine reagents (Scheme , route c) . In fact, previous work on the reaction between thioether or dimethyl sulfide with these high‐valent iodine reagents, such as chloramine T‐type high‐valent iodines, has been reported by others .…”

Chemical Methods for Selective Labeling of Proteins

“…In a recent report, Chang's group reported a redox activated chemical tagging (ReACT) where an oxaziridine results in the chemoselective transformation of methionine to sulfimides . In parallel, the hypervalent iodine reagent (iodonium salt) was used for the modification of methionine (Scheme c) . The reagents incorporate acyl groups functionalized with a diazo group making it amenable for late‐stage photocatalytic modifications.…”

Covalent Small Molecules as Enabling Platforms for Drug Discovery

“…Methionine does not possess the inherent nucleophilicity of cysteine, explaining its limited attention to date. Two recent publications have utilised hypervalent iodine reagents and redox‐active oxiridine systems to covalently modify methionine residues in native proteomes, thus interest in this residue is likely to increase …”