Site-selective photocatalytic functionalization of peptides and proteins at selenocysteine

Abstract

The importance of modified peptides and proteins for applications in drug discovery, and for illuminating biological processes at the molecular level, is fueling a demand for efficient methods that facilitate the precise modification of these biomolecules. Herein, we describe the development of a photocatalytic method for the rapid and efficient dimerization and site-specific functionalization of peptide and protein diselenides. This methodology, dubbed the photocatalytic diselenide contraction, involves irradiation at 450 nm in the presence of an iridium photocatalyst and a phosphine and results in rapid and clean conversion of diselenides to reductively stable selenoethers. A mechanism for this photocatalytic transformation is proposed, which is supported by photoluminescence spectroscopy and density functional theory calculations. The utility of the photocatalytic diselenide contraction transformation is highlighted through the dimerization of selenopeptides, and by the generation of two families of protein conjugates via the site-selective modification of calmodulin containing the 21st amino acid selenocysteine, and the C-terminal modification of a ubiquitin diselenide.

Selenium in Peptide Chemistry

“…Moreover, the formation of a selenolanthionine bridge from cyclic peptides involving both intramolecular diselenide and disulfide bonds was achieved in 10 min of irradiation without affecting the disulfide bond [ 90 ]. A similar reaction was later described by Dowman et al [ 131 ], who demonstrated the photocatalytic diselenide contraction to yield selenoethers. This transformation was induced by irradiation of Sec-containing dimers in the presence of the phosphine 1,3,5-triaza-7-phosphaadamantane (PTA) and the iridium photocatalyst, [Ir(dF(CF 3 )ppy) 2 (dtbpy)]PF 6 , under LED 450 irradiation within 5 min.…”

Electrochemical Modification of Polypeptides at Selenocysteine

“…A large anodic oxidation signal was observed at 1.05 V, corresponding to the oxidation of TPPTS to the radical cation (as seen in Figure 2A). We postulated that following oxidation, the electrochemical modification strategy would proceed through an analogous single‐electron mechanism to that proposed for photocatalytic contraction reactions at Sec [7a] . Briefly, we hypothesized that the radical cation generated from anodic oxidation of the phosphine would induce homolytic diselenide cleavage, with cathodic reduction of the resultant selanyl radical generating one equivalent of a highly nucleophilic selenolate (Figure 2B).…”

“…The development of this proposed electrochemical modification chemistry took inspiration from a photocatalytic diselenide contraction (PDC) transformation recently developed in our laboratory (Figure 1A). [7a] The PDC method employs an iridium photocatalyst ([Ir(dF(CF 3 )ppy) 2 (dtbpy)]PF 6 ) together with a phosphine and irradiation at 450 nm to convert asymmetric or symmetric diselenide starting materials to their corresponding selenoether‐linked products, with formal extrusion of a selenium atom. We sought to overcome key limitations of this methodology, including incompatibility with fluorogenic substrates and the use of expensive and poorly aqueous soluble photocatalysts, through the development of a low cost, atom economic, and biocompatible electrochemical method for site‐selective functionalization of Sec residues, coined electrochemical selenoetherification (e‐SE).…”

Meeting Proceedings from ICBS 2022 – Uncovering Solutions for Diseases

“…They also reported conversion of dimeric peptide diselenides to dimeric peptide selenoethers with phosphine, an iridium photocatalyst, and light, which can be applied to late-stage modification of synthetic peptides. 71 Andrey A. Ivanov (Emory University, USA) shared protein−protein interactions (PPIs) in breast cancer discovered with their quantitative high-throughput differential screening (qHT-dS), which was first shared at ICBS 2017 and used in wildtype and mutant systems of lung cancer and other cancers. 72 The qHT-dS platform discovered mitogen-activated kinase kinase 3 (MKK3), previously only known to activate tumor suppressor p38 by phosphorylation, to activate the transcription factor MYC by PPI.…”

“…The technique was used to generate other proteins and adapted for protein generation in one pot. They also reported conversion of dimeric peptide diselenides to dimeric peptide selenoethers with phosphine, an iridium photocatalyst, and light, which can be applied to late-stage modification of synthetic peptides …”