Research progress on chemical modifications of tyrosine residues in peptides and proteins

The chemical modifications (CMs) of protein is an important technique in chemical biology, protein-based therapy, and material science. In recent years, there has been rapid advances in the development of CMs of peptides and proteins, providing new approaches for peptide and protein functionalization, as well as drug discovery. In this review, we highlight the methods for chemically modifying tyrosine (Tyr) residues in different regions, offering a comprehensive exposition of the research content related to Tyr modification. This review summarizes and provides an outlook on Tyr residue modification, aiming to offer readers assistance in the site-selective modification of macromolecules and to facilitate application research in this field.

Site-Selective Tyrosine Reaction for Antibody-Cell Conjugation and Targeted Immunotherapy

Targeted immunotherapies capitalize on the exceptional binding capabilities of antibodies to stimulate a host response that effectuates long-lived tumor destruction. One example is the conjugation of immunoglobulins (IgGs) to immune effector cells, which equips the cells with the ability to recognize and accurately kill malignant cells through a process called antibody-dependent cellular cytotoxicity (ADCC). In this study, a chemoenzymatic reaction is developed that specifically functionalizes a single tyrosine (Tyr, Y) residue, Y296, in the Fc domain of therapeutic IgGs. A one-pot reaction that combines the tyrosinase-catalyzed oxidation of tyrosine to o-quinone with a subsequent [3+2] photoaddition with vinyl ether is employed. This reaction installs fluorescent molecules or bioorthogonal groups at Y296 of IgGs or the C-terminal Y-tag of an engineered nanobody. The Tyr-specific reaction is utilized in constructing monofunctionalized antibody-drug conjugates (ADCs) and antibody/nanobody-conjugated effector cells, such as natural killer cells or macrophages. These results demonstrate the potential of site-selective antibody reactions for enhancing targeted cancer immunotherapy.

A triple-diazonium reagent for virus crosslinking and the synthesis of an azo-linked molecular cage

The first bench-stable triple-diazonium reagent (TDA-1) was rationally designed and synthesized for coupling and crosslinking. The three reactive sites of TDA-1 can react with phenol-containing molecules as well as plant viruses in aqueous buffers efficiently. In addition, a new-type azo-linked cage was constructed by the direct reaction of TDA-1 with a triple-phenol molecule and was characterized by X-ray crystallography.

Virus-Based Supramolecular Structure and Materials: Concept and Prospects

Rodlike and spherelike viruses are various monodisperse nanoparticles that can display small molecules or polymers with unique distribution following chemical modifications. Because of the monodisperse property, aggregates in synthetic protein-polymer nanoparticles could be eliminated, thus improving the probability for application in protein-polymer drug. In addition, the monodisperse virus could direct the growth of metal materials or inorganic materials, finding applications in hydrogel, drug delivery, and optoelectronic and catalysis materials. Benefiting from the advantages, the virus or viruslike particles have been widely explored in the field of supramolecular chemistry. In this review, we describe the modification and application of virus and viruslike particles in surpramolecular structures and biomedical research.

Bio-Orthogonal Conjugation of a Cationic Metalloporphyrin to BSA and HSA via "Click" Chemistry

In this study, we present a convenient method for the labelling of tyrosine residues on bovine serum albumin (BSA) and human serum albumin (HSA) and report for the first time their subsequent bio-orthogonal conjugation with porphyrins via "click" chemistry. We demonstrate that these serum proteins can be labelled with an alkyne-diazonium heterobifunctional linker and can then undergo chemo-selective bio-orthogonal conjugation with a water-soluble azido metalloporphyrin via "click" chemistry to yield protein-conjugates that retain their photodynamic properties. In our hands, this method was found to be highly reproducible, scalable, and tuneable which allows for the production of bioconjugates where the porphyrin-protein conjugate not only retains an ability to generate singlet oxygen but possess an enhanced relative singlet oxygen quantum yields relative to the porphyrin alone. Furthermore, we have investigated the photochemical properties of these conjugates through photospectrometric techniques and have determined that the porphyrin macrocycles remain appreciably photostable under light irradiation. Our phototoxic protein-photosensitizer-conjugates show excellent photodynamic activity against a human colorectal adenocarcinoma cancer cell line (HT-29) with cell viabilities of 7.7±0.5 % (IC50 8.76±2.14 μM) and 1.7±1.9 % (IC50 8.48±5.11 μM) for BSA and HAS, respectively, when irradiated with 20 J cm^-2 of white-light. Importantly, neither of the conjugates was found to possess any significant "dark" toxicity even at concentrations of 100 μM. Furthermore, the natural fluorescent properties of the bioconjugates allowed for the determination of cellular uptake in vitro via fluorescence microscopy thus highlighting the potential theranostic applications of these unique protein-drug-conjugates.

Site-Selective Functionalization of Methionine Residues via Photoredox Catalysis

Bioconjugation technologies have revolutionized the practice of biology and medicine by allowing access to novel biomolecular scaffolds. New methods for residue-selective bioconjugation are highly sought to expand the toolbox for a variety of bioconjugation applications. Herein we report a site-selective methionine bioconjugation protocol that uses photoexcited lumiflavin to generate open-shell intermediates. This reduction-potential-gated strategy enables access to residues unavailable with traditional nucleophilicity-based conjugation methods. To demonstrate the versatility and robustness of this new protocol, we have modified various proteins and further utilized this functional handle to append diverse biological payloads.

Light-Activatable, 2,5-Disubstituted Tetrazoles for the Proteome-wide Profiling of Aspartates and Glutamates in Living Bacteria

Covalent inhibitors have recently seen a resurgence of interest in drug development. Nevertheless, compounds, which do not rely on an enzymatic activity, have almost exclusively been developed to target cysteines. Expanding the scope to other amino acids would be largely facilitated by the ability to globally monitor their engagement by covalent inhibitors. Here, we present the use of light-activatable 2,5-disubstituted tetrazoles that allow quantifying 8971 aspartates and glutamates in the bacterial proteome with excellent selectivity. Using these probes, we competitively map the binding sites of two isoxazolium salts and introduce hydrazonyl chlorides as a new class of carboxylic-acid-directed covalent protein ligands. As the probes are unreactive prior to activation, they allow global profiling even in living Gram-positive and Gram-negative bacteria. Taken together, this method to monitor aspartates and glutamates proteome-wide will lay the foundation to efficiently develop covalent inhibitors targeting these amino acids.

Modifications of amino acids using arenediazonium salts

Aryl transfer reactions from arenediazonium salts have started to make their impact in chemical biology with initial forays in the arena of arylative modifications and bio-conjugations of amino acids, peptides and proteins.

Development of improved dual-diazonium reagents for faster crosslinking of tobacco mosaic virus to form hydrogels

New bench-stable reagents with two diazonium sites were designed and synthesized for protein crosslinking. Because of the faster diazonium-tyrosine coupling reaction, hydrogels from the crosslinking of tobacco mosaic virus and the reagent DDA-3 could be prepared within 1 min at room temperature. Furthermore, hydrogels with the introduction of disulfide bonds viaDDA-4 could be chemically degraded by dithiothreitol. Our results provided a facile approach for the direct construction of virus-based hydrogels.

Improved dual-diazonium reagents were developed for more efficient crosslinking of tobacco mosaic virus to form hydrogels.

A convenient method for multicolour labelling of proteins with BODIPY fluorophores via tyrosine residues

Fluorescence is an essential imaging modality for labelling and visualising cells and sub-cellular structures. Multicolour labelling is especially challenging due to differences in physicochemical and photophysical behaviour of structurally unrelated fluorophores in the heterogeneous environments found in sub-cellular compartments. Herein, we report the conjugation of three azide-bearing BODIPYs with similar core structures but widely different emission wavelengths (green, red and NIR) to tyrosine residues of a model globular protein (BSA) via a common linking methodology. The resulting BODIPY-BSA conjugates have demonstrated multi-wavelength fluorescence emission for biological applications. Fluorescence imaging was performed in HeLa cells through live cell confocal microscopy imaging, with good intracellular location visualisation observed.

A highly efficient dual-diazonium reagent for protein crosslinking and construction of a virus-based gel

A highly efficient strategy is developed to construct a new hydrogel using tobacco mosaic virus and a new bench-stable diazonium reagent.

Cu-Click Compatible Triazabutadienes To Expand the Scope of Aryl Diazonium Ion Chemistry

Triazabutadienes can be used to readily generate reactive aryl diazonium ions under mild, physiologically relevant conditions. These conditions are compatible with a range of functionalities that do not tolerate traditional aryl diazonium ion generation. To increase the utility of this aryl diazonium ion releasing chemistry an alkyne-containing triazabutadiene was synthesized. The copper-catalyzed azide-alkyne cycloaddition ("Cu-click") reaction was utilized to modify the alkyne-containing triazabutadiene and shown to be compatible with the nitrogen-rich triazabutadiene. One of the triazole products was tethered to a fluorophore, thus enabling the direct fluorescent labeling of a model protein.

CuAAC click reactions for the design of multifunctional luminescent ruthenium complexes

CuAAC (Cu(i) catalyzed azide–alkyne cycloaddition) click chemistry has emerged as a versatile tool in the development of photoactive ruthenium complexes with multilateral potential applicability. Three general concepts for their synthesis and selected applications are discussed.

Protein tetrazinylation via diazonium coupling for covalent and catalyst-free bioconjugation

This work reports an efficient reagent 1 for direct and covalent introduction of tetrazines onto the surface of proteins and viruses under mild conditions.