Developments and recent advancements in the field of endogenous amino acid selective bond forming reactions for bioconjugation

Sulfur(IV) Chemistry-Based Peptide and Protein Late-Stage Modification

The development of precise and controllable chemical modification tools for peptides and proteins represents a great challenge in elucidating their structure-activity relationships and regulatory mechanisms, as well as a powerful driver for advancing macromolecular therapeutic strategies. However, current technologies predominantly rely on irreversible covalent labeling or genetic encoding of unnatural amino acids, exhibiting significant limitations in reversible modification, in situ functional regulation, and adaptability to complex physiological environments. In recent years, breakthrough advancements in sulfur(IV) chemistry have provided a paradigm for the late-stage functionalization of peptides and proteins. Through synergistic innovations in sulfur(IV)-based reagent design, intermediate modulation, and bioorthogonal reactions, a more multifaceted modification toolbox has been progressively established, integrating site selectivity, condition responsiveness, and functional rescue. Providing current challenges and future perspectives in this field, this review focuses on sulfur(IV) chemistry-driven strategies for peptide and protein modification, as well as their applications in proximity-labeling strategies and drug delivery/therapeutic interventions.

A palette of bridged bicycle-strengthened fluorophores

Organic fluorophores are the keystone of advanced biological imaging. The vast chemical space of fluorophores has been extensively explored in search of molecules with ideal properties. However, within the current molecular constraints, there appears to be a trade-off between high brightness, robust photostability, and tunable biochemical properties. Herein we report a general strategy to systematically boost the performance of donor-acceptor-type fluorophores, such as rhodamines, by leveraging SO2 and O-substituted azabicyclo[3.2.1] octane auxochromes. These bicyclic heterocycles give rise to a collection of 'bridged' dyes (BD) spanning the ultraviolet and visible range with top-notch quantum efficiencies, enhanced water solubility, and tunable cell-permeability. Notably, these azabicyclic fluorophores showed remarkable photostability compared to their tetramethyl or azetidine analogs while being completely resistant to oxidative photoblueing. Functionalized BD dyes are tailored for applications in single-molecule imaging, super-resolution imaging (STED and SIM) in fixed or live mammalian and plant cells, and live zebrafish imaging and chemogenetic voltage imaging.

Systematic kinetic assay of phenylsulfonyl pyridine derivatives with free thiol for site-specific modification of proteins

Site-specific modification of proteins with functional groups is a powerful way of understanding the dynamics and functions of proteins. Recently reported phenylsulfonyl pyridine is a thiol-specific moiety and is of great interest for the use of high resolution nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) in structural biology. However, the reactivity of phenylsulfonyl pyridines to free thiols was barely understood, especially considering the effect of the substituent groups in pyridine on the kinetic activity. In this work, we used a number of phenylsulfonyl pyridine derivatives and systematically evaluated the kinetic properties of these compounds with free cysteine at different pHs by means of NMR and UV spectroscopy. The experimental results show that the reactivity of phenylsulfonyl pyridines with free thiols can be tuned by substitution of pyridine or metal ion coordination, with a range of reaction rates from one to five orders of magnitude. These kinetic parameters provide valuable insights into the protein site-specific modification by the phenylsulfonyl pyridine moiety, as demonstrated in the present study.

Characterisation and correction of polarisation effects in fluorescently labelled fibres

Many biological structures take the form of fibres and filaments, and quantitative analysis of fibre organisation is important for understanding their functions in both normal physiological conditions and disease. In order to visualise these structures, fibres can be fluorescently labelled and imaged, with specialised image analysis methods available for quantifying the degree and strength of fibre alignment. Here we show that fluorescently labelled fibres can display polarised emission, with the strength of this effect varying depending on structure and fluorophore identity. This can bias automated analysis of fibre alignment and mask the true underlying structural organisation. We present a method for quantifying and correcting these polarisation effects without requiring polarisation-resolved microscopy and demonstrate its efficacy when applied to images of fluorescently labelled collagen gels, allowing for more reliable characterisation of fibre microarchitecture.

Proximity-induced SuFEx increases the potency of cytosolic nucleotidase inhibitors and reveals a rare example of covalently targeted histidine

Structure-guided design is one of the most validated solutions for targeting proteins with specific ligands for therapeutic purposes. Nevertheless, it remains challenging to target enzymes with low affinity for their natural ligands and specificities that overlap with those of other proteins. Cytosolic 5'-nucleotidases - involved in the metabolism of nucleic acid derivatives - are an example of such a family. Here we illustrate how precisely designed covalent inhibitors represent a potential solution for selective nucleotidase targeting. We employed the sulfur-fluoride exchange (SuFEx) to develop a covalent inhibitor of cytosolic nucleotidase IIIB (cNIIIB). Using the known inhibitor (7-benzylguanosine monophosphate, Bn7GMP) and computational methods, we designed and synthesized a series of SuFExable inhibitors. One compound indeed covalently bound cNIIIB, which increased the inhibition potency by over 100-fold. The formation of a covalent S-N bond with a non-catalytic His110 residue was confirmed through MS and 15N NMR. The selectivity of the compound in the context of other protein that recognises similar ligands was also confirmed. The study expands the principle of covalent inhibition of nucleotide processing enzymes. It also represents a rare example of histidine tagging by SuFEx. This may facilitate the broader application of SuFEx chemistry in biochemistry and medicinal chemistry.

Visible Light-Mediated Diastereoselective Synthesis of Novel Glycopeptide Mimetics

Herein, we introduce a mild and operationally simple visible-light photochemistry protocol for the synthesis of novel glycopeptide mimetics. This method capitalizes on the reaction between 1,4-dihydropyridine (DHP) containing amino acids and peptides with glycosyl nitrones, showing exceptional stereoselectivity and robust performance across a diverse array of substrates, encompassing both modified glycosides and intricate peptide structures. Furthermore, we underscore the versatility of the resultant compounds through their seamless integration and utility in bioconjugation strategies.

Formamidine as an Easy-On and Easy-Off Linker for Reversible Crosslinking of Two Alkyl Amines in Peptide Stapling and Conjugation

Amino groups are abundant in both natural and synthetic molecules, offering highly accessible sites for modifying native biorelevant molecules. Despite significant progress with more reactive thiol groups, methods for ligating two amino groups with reversible linkers for bioconjugation applications remain elusive. Herein, we report the use of oxidative decarboxylative condensation of glyoxylic acid to crosslink or ligate two alkyl amines via a compact formamidine linkage, applicable in both intra- and intermolecular contexts. This linking chemistry exhibits unique hetero-coupling selectivity between primary and secondary alkyl amines. Although the formamidine linkage is stable under pH-neutral buffers and acidic conditions, it can be readily cleaved with ethylenediamine or hydrazine under mild conditions in alcohol solvents or aqueous media, fully restoring the amino groups. This study introduces a rare 'easy-on and easy-off' strategy for connecting two native amines in peptide stapling and biomolecule conjugation.

Targeted Covalent Modification Strategies for Drugging the Undruggable Targets

The term "undruggable" refers to proteins or other biological targets that have been historically challenging to target with conventional drugs or therapeutic strategies because of their structural, functional, or dynamic properties. Drugging such undruggable targets is essential to develop new therapies for diseases where current treatment options are limited or nonexistent. Thus, investigating methods to achieve such drugging is an important challenge in medicinal chemistry. Among the numerous methodologies for drug discovery, covalent modification of therapeutic targets has emerged as a transformative strategy. The covalent attachment of diverse functional molecules to targets provides a powerful platform for creating highly potent drugs and chemical tools as well the ability to provide valuable information on the structures and dynamics of undruggable targets. In this review, we summarize recent examples of chemical methods for the covalent modification of proteins and other biomolecules for the development of new therapeutics and to overcome drug discovery challenges and highlight how such methods contribute toward the drugging of undruggable targets. In particular, we focus on the use of covalent chemistry methods for the development of covalent drugs, target identification, drug screening, artificial modulation of post-translational modifications, cancer specific chemotherapies, and nucleic acid-based therapeutics.

Selective Protein (Post-)modifications through Dynamic Covalent Chemistry: Self-activated SNAr Reactions

SNAr reactions were remarkably accelerated using a pretargeting and activating unit based on dynamic covalent chemistry (DCvC). A Cys attack at the C-F bond on the aromatic ring of salicylaldehyde derivatives was only observed upon iminium formation with a neighboring Lys residue of model small peptides. Such self-activation was ascribed to the stronger electron-withdrawing capability of the iminium bond with respect to that of the parent aldehyde that stabilized the transition state of the reaction, together with the higher preorganization of the reactive groups in the cationic aldiminium species. This approach was further applied for the functionalization of two antibodies. In both cases, the presence of the aldehyde group in close proximity to the reactive C-F bond resulted in a noteworthy increase in bioconjugation yields, with excellent chemo-selectivity. Whereas the modification of an IgG1 antibody led to stochastic product distributions, microenvironment selectivity was noted when employing IgG4, in line with the lower number of Lys residues in the hinge region of the latter. Additionally, the postfunctionalization of the modified antibodies was attained through the dynamic covalent exchange of the tethered iminium derivative with hydrazides, representing an unprecedented "tag and modify" selective bioconjugation strategy based on DCvC.

Molecular Matchmakers: Bioconjugation Techniques Enhance Prodrug Potency for Immunotherapy

Cancer patients suffer greatly from the severe off-target side effects of small molecule drugs, chemotherapy, and radiotherapy─therapies that offer little protection following remission. Engineered immunotherapies─including cytokines, immune checkpoint blockade, monoclonal antibodies, and CAR-T cells─provide better targeting and future tumor growth prevention. Still, issues such as ineffective activation, immunogenicity, and off-target effects remain primary concerns. "Prodrug" therapies─classified as therapies administered as inactive and then selectively activated to control the time and area of release─hold significant promise in overcoming these concerns. Bioconjugation techniques (e.g., natural linker conjugation, bioorthogonal reactions, and noncanonical amino acid incorporation) enable the rapid and homogeneous synthesis of prodrugs and offer selective loading of immunotherapeutic agents to carrier molecules and protecting groups to prevent off-target effects after administration. Several prodrug activation mechanisms have been highlighted for cancer therapeutics, including endogenous activation by hypoxic or acidic conditions common in tumors, exogenous activation by targeted bioorthogonal cleavage, or stimuli-responsive light activation, and dual-stimuli activation, which adds specificity by combining these mechanisms. This review will explore modern prodrug conjugation and activation options, focusing on how these strategies can enhance immunotherapy responses and improve patient outcomes. We will also discuss the implications of computational methodology for therapy design and recommend procedures to determine how and where to conjugate carrier systems and "prodrug" groups onto therapeutic agents to enhance the safety and control of these delivery platforms.

Recent advances in peptide macrocyclization strategies

Recently, owing to their special spatial structures, peptide-based macrocycles have shown tremendous promise and aroused great interest in multidisciplinary research ranging from potent antibiotics against resistant strains to functional biomaterials with novel properties. Besides traditional monocyclic peptides, many fascinating polycyclic and remarkable higher-order cyclic, spherical and cylindric peptidic systems have come into the limelight owing to breakthroughs in various chemical (e.g., native chemical ligation and transition metal catalysis), biological (e.g., post-translational enzymatic modification and genetic code reprogramming), and supramolecular (e.g., mechanically interlocked, metal-directed folding and self-assembly via noncovalent interactions) macrocyclization strategies developed in recent decades. In this tutorial review, diverse state-of-the-art macrocyclization methodologies and techniques for peptides and peptidomimetics are surveyed and discussed, with insights into their practical advantages and intrinsic limitations. Finally, the synthetic-technical aspects, current unresolved challenges, and outlook of this field are discussed.

Target Bioconjugation of Protein Through Chemical, Molecular Dynamics, and Artificial Intelligence Approaches

Covalent modification of proteins at specific, predetermined sites is essential for advancing biological and biopharmaceutical applications. Site-selective labeling techniques for protein modification allow us to effectively track biological function, intracellular dynamics, and localization. Despite numerous reports on modifying target proteins with functional chemical probes, unique organic reactions that achieve site-selective integration without compromising native functional properties remain a significant challenge. In this review, we delve into site-selective protein modification using synthetic probes, highlighting both chemical and computational methodologies for chemo- and regioselective modifications of naturally occurring amino acids, as well as proximity-driven protein-selective chemical modifications. We also underline recent traceless affinity labeling strategies that involve exchange/cleavage reactions and catalyst tethering modifications. The rapid development of computational infrastructure and methods has made the bioconjugation of proteins more accessible, enabling precise predictions of structural changes due to protein modifications. Hence, we discuss bioconjugational computational approaches, including molecular dynamics and artificial intelligence, underscoring their potential applications in enhancing our understanding of cellular biology and addressing current challenges in the field.

Development of molecular sensors based on fluorescent proteins for polarized macrophages identification

Macrophages are a type of white blood cells that play key roles in innate immune responses as a part of cellular immunity for host defence and tissue homeostasis. To perform diverse functions, macrophages show high plasticity by transforming to polarized states. They are mainly identified as unpolarized, pro-inflammatory and antiinflammatory states and termed as M0, M1 and M2 macrophages respectively. Discriminating polarized states is important due to strict implication with inflammatory conditions resulting in many diseases as chronic inflammation, neurodegeneration, and cancer etc. Many polarization protein markers have been identified and applied to investigate expression profiles through PCR and other techniques with antibodies. However, they are time and cost consuming and sometimes show insufficient performances. We focused on the mannose receptor (CD206) as representative marker of M2 macrophage recognising terminal mannose. We developed dose dependent mannosylated fluorescent proteins (FPs) by conjugations with mannose derivative for around 20 modifiable sites on FPs surfaces. Maximum modifications did not spoil various features of FPs. We found further sensitive and specific discriminations among M2, M1 and M0 macrophages after treating polarized macrophages with adequately conditioned FPs compared to already established approaches using anti CD206 antibody through flow cytometric analysis. These results might be derived from direct ligand utilizations and increased avidity due to multivalent bindings with abundantly modified multimeric FPs. Our strategy is simple but addresses disadvantages of preceding methods. Moreover, this strategy is applicable to detect other cell surface receptors as FPs can be modified with ligands or recognizable aptamer like molecules.

ClickGen: Directed exploration of synthesizable chemical space via modular reactions and reinforcement learning

Despite the significant potential of generative models, low synthesizability of many generated molecules limits their real-world applications. In response to this issue, we develop ClickGen, a deep learning model that utilizes modular reactions like click chemistry to assemble molecules and incorporates reinforcement learning along with inpainting technique to ensure that the proposed molecules display high diversity, novelty and strong binding tendency. ClickGen demonstrates superior performance over the other reaction-based generative models in terms of novelty, synthesizability, and docking conformation similarity for existing binders targeting the three proteins. We then proceeded to conduct wet-lab validation on the ClickGen's proposed molecules for poly adenosine diphosphate-ribose polymerase 1. Due to the guaranteed high synthesizability and model-generated synthetic routes for reference, we successfully produced and tested the bioactivity of these novel compounds in just 20 days, much faster than typically expected time frame when handling sufficiently novel molecules. In bioactivity assays, two lead compounds demonstrated superior anti-proliferative efficacy against cancer cell lines, low toxicity, and nanomolar-level inhibitory activity to PARP1. We demonstrate that ClickGen and related models may represent a new paradigm in molecular generation, bringing AI-driven, automated experimentation and closed-loop molecular design closer to realization.

Bioorthogonal Synthetic Chemistry Enabled by Visible-Light Photocatalysis

The field of bioorthogonal chemistry has revolutionized our ability to interrogate and manipulate biological systems at the molecular level. However, the range of chemical reactions that can operate efficiently in biological environments without interfering with the native cellular machinery, remains limited. In this context, the rapidly growing area of photocatalysis offers a promising avenue for developing new type of bioorthogonal tools. The inherent mildness, tunability, chemoselectivity, and external controllability of photocatalytic transformations make them particularly well-suited for applications in biological and living systems. This minireview summarizes recent advances in bioorthogonal photocatalytic technologies, with a particular focus on their potential to enable the selective generation of designed products within biologically relevant or living settings.

Durability improvement strategies for wettable fog harvesting devices inspired by spider silk fibers: a review

Water scarcity is a persistent challenge, and in this case, the freshwater content in the air and water collection phenomena observed in nature provide ideas for fog harvesting. The fog-harvesting capabilities of natural spider silk have long attracted attention. Thus, researchers have undertaken significant efforts for the preparation of wettable biomimetic knotted fibers. However, the fragility of their chemical coating and the susceptibility of spun fibers to damage often present substantial challenges in the durability of fog harvesting equipment. Herein, from a bioengineering perspective, we review the improvement strategies for enhancing the mechanical properties of wettable biomimetic spider silk fibers based on the dense nanoconfined hydrogen-bond array crystalline regions and uniformly embedded amorphous regions of natural wettable spider silk fibers. These strategies aim to achieve high tensile strength, good fracture toughness, and corrosion resistance. Additionally, by incorporating UV inhibitors during spinning, the effects of sunlight can be mitigated or shielded, thereby greatly enhancing the mechanical durability of fog-harvesting devices under harsh realistic conditions.

Conductance Channels in a Single-Entity Enzyme

For a long time, the prevailing view in the scientific community was that proteins, being complex macromolecules composed of amino acid chains linked by peptide bonds, adopt folded structure with insulating or semiconducting properties, with high bandgaps. However, recent discoveries of unexpectedly high conductance levels, reaching values in the range of dozens of nanosiemens (nS) in proteins, have challenged this conventional understanding. In this study, we used scanning tunneling microscopy (STM) to explore the single-entity conductance properties of enzymatic channels, focusing on bilirubin oxidase (BOD) as a model metalloprotein. By immobilizing BOD on a conductive carbon surface, we discern its preferred orientation, facilitating the formation of electronic and ionic channels. These channels show efficient electron transport (ETp), with apparent conductance up to the 15 nS range. Notably, these conductance pathways are localized, minimizing electron transport barriers due to solvents and ions, underscoring BOD's redox versatility. Furthermore, electron transfer (ET) within the BOD occurs via preferential pathways. The alignment of the conductance channels with hydrophilicity maps, molecular vacancies, and regions accessible to electrolytes explains the observed conductance values. Additionally, BOD exhibits redox activity, with its active center playing a critical role in the ETp process. These findings significantly advance our understanding of the intricate mechanisms that govern ETp processes in proteins, offering new insights into the conductance of metalloproteins.

Luminescent lanthanide metallopeptides for biomolecule sensing and cellular imaging

Lanthanide ions display unique luminescent properties that make them particularly attractive for the development of bioprobes, including long-lived excited states that allow the implementation of time-gated experiments and the elimination of background fluorescence associated with biological media, as well as narrow emission bands in comparison with typical organic fluorophores, which allow ratiometric and multiplex assays. These luminescent complexes can be combined with peptide ligands to endow them with additional targeting, responsiveness, and selectivity, thus multiplying the opportunities for creative probe design. In this feature article we will present some of the main strategies that researchers have used to develop lanthanide metallopeptide probes for the detection of proteins and nucleic acids, as well as for monitoring enzymatic activity and cellular imaging.

Fast and Selective Cysteine Conjugation Using para-Quinone Methides

An efficient and selective method for cysteine conjugation utilizing para-quinone methides (p-QMs) was developed. p-QM labeling exhibits high specificity toward the cysteine residue, as evidenced by its reactivity with various amino acid derivatives, peptides, and proteins. Notably, the p-QM-cysteine reactions display robust kinetics with rate constants up to 1.67 × 104 M-1·s-1. Furthermore, p-QM conjugation enables us to attach a fluorescent probe to a HER2 nanobody, resulting in selective labeling of HER2-positive SK-BR-3 cells.

Introducing Chemoselective Peptide Conjugation via N-Alkylation of Pyridyl-alanine: Solution and Solid Phase Applications

A novel chemoselective peptide conjugation via late-stage N-alkylation of pyridyl-alanine (PAL) in the solution and solid phase, namely, NAP, is demonstrated. The method constructs functionally diverse and highly stable N-alkylated conjugates with various peptides. Notably, conjugations in the solid phase offered a more economical process. The method can provide the opportunity for dual labeling along with a cysteine handle in a peptide chain. Finally, we showcased that the antiproliferative activities of the p53 peptide (MDM2 inhibitor) could be 2-fold enhanced via NAP conjugation with the RGD peptide (selective integrin binder).

Peptide and Protein Cysteine Modification Enabled by Hydrosulfuration of Ynamide

Efficient functionalization of peptides and proteins has widespread applications in chemical biology and drug discovery. However, the chemoselective and site-selective modification of proteins remains a daunting task. Herein, a highly efficient chemo-, regio-, and stereoselective hydrosulfuration of ynamide was identified as an efficient method for the precise modification of peptides and proteins by uniquely targeting the thiol group of cysteine (Cys) residues. This novel method could be facilely operated in aqueous buffer and was fully compatible with a wide range of proteins, including small model proteins and large full-length antibodies, without compromising their integrity and functions. Importantly, this reaction provides the Z-isomer of the corresponding conjugates exclusively with superior stability, offering a precise approach to peptide and protein therapeutics. The potential application of this method in peptide and protein chemical biology was further exemplified by Cys-bioconjugation with a variety of ynamide-bearing functional molecules such as small molecule drugs, fluorescent/affinity tags, and PEG polymers. It also proved efficient in redox proteomic analysis through Cys-alkenylation. Overall, this study provides a novel bioorthogonal tool for Cys-specific functionalization, which will find broad applications in the synthesis of peptide/protein conjugates.

β-Silyl alkynoates: Versatile reagents for biocompatible and selective amide bond formation

The study introduces a previously unidentified method for amide bond formation that addresses several limitations of conventional approaches. It uses the β-silyl alkynoate molecule, where the alkynyl group activates the ester for efficient amide formation, while the bulky TIPS (triisopropylsilane) group prevents unwanted 1,4-addition reactions. This approach exhibits high chemoselectivity for amines, making the method compatible with a wide range of substrates, including secondary amines, and targets the specific ε-amino group of lysine among the native amino ester's derivatives. It maintains stereochemistry during amide bond formation and TIPS group removal, allowing a versatile platform for postsynthesis modifications such as click reactions and peptide-drug conjugations. These advancements hold substantial promise for pharmaceutical development and peptide engineering, opening avenues for research applications.

A thiol-selective and acid-stable protein modification strategy using an electron-deficient yne reagent

A protein modification strategy was developed based on a thiol-yne click reaction using an electron-deficient yne reagent. This approach demonstrated exceptional selectivity towards thiols and exhibited rapid kinetics, resulting in conjugates with superior acid stability. The conjugation of IgG with an indole-derived fluorophore was achieved for the imaging of PD-L1 in cancer cells.

Methods to monitor mitochondrial disulfide bonds

Mitochondria contain numerous proteins that utilize the chemistry of cysteine residues, which can be reversibly oxidized. These proteins are involved in mitochondrial biogenesis, protection against oxidative stress, metabolism, energy transduction to adenosine triphosphate, signaling and cell death among other functions. Many proteins located in the mitochondrial intermembrane space are imported by the mitochondrial import and assembly pathway the activity of which is based on the reversible oxidation of cysteine residues and oxidative trapping of substrates. Oxidative modifications of cysteine residues are particularly difficult to study because of their labile character. Here we present techniques that allow for monitoring the oxidative state of mitochondrial proteins as well as to investigate the mitochondrial import and assembly pathway. This chapter conveys basic concepts on sample preparation and techniques to monitor the redox state of cysteine residues in mitochondrial proteins as well as the strategies to study mitochondrial import and assembly pathway.

Cysteinylprolyl ester-mediated drug release from a lipid-drug conjugate

For small-molecule drugs, lipidation via a cleavable linkage can extend half-life in circulation through interaction with albumin. Here we modified the cysteinylprolyl ester (CPE) system used in peptide thioester synthesis, which normally requires basic conditions, for use as an self-immolative linker and release device for a lipid-gemcitabine conjugate. To improve release under physiological conditions for medical application, a methyl group at the α-position of cysteine on the CPE unit was incorporated in anticipation of the Thorpe-Ingold effect. As a result, Ac-Gly-(α-Me)Cys(SH)-Pro-gemcitabine 11 drastically promoted the release of gemcitabine in comparison with Ac-Gly-Cys(SH)-Pro-gemcitabine 10. Furthermore, in the presence of bovine serum albumin and/or 2-mercaptoethanesulfonic acid, the gentle and continuous release of gemcitabine from the lipid-gemcitabine conjugate 16 was achieved. In addition to gemcitabine, this method could allow high clearance drugs, including nucleic acid and prostacyclin derivatives, to maintain their biological activity long enough to become effective.

Strategies for Making High-Performance Artificial Spider Silk Fibers

Artificial spider silk is an attractive material for many technical applications since it is a biobased fiber that can be produced under ambient conditions but still outcompetes synthetic fibers (e.g., Kevlar) in terms of toughness. Industrial use of this material requires bulk-scale production of recombinant spider silk proteins in heterologous host and replication of the pristine fiber's mechanical properties. High molecular weight spider silk proteins can be spun into fibers with impressive mechanical properties, but the production levels are too low to allow commercialization of the material. Small spider silk proteins, on the other hand, can be produced at yields that are compatible with industrial use, but the mechanical properties of such fibers need to be improved. Here, the literature on wet-spinning of artificial spider silk fibers is summarized and analyzed with a focus on mechanical performance. Furthermore, several strategies for how to improve the properties of such fibers, including optimized protein composition, smarter spinning setups, innovative protein engineering, chemical and physical crosslinking as well as the incorporation of nanomaterials in composite fibers, are outlined and discussed.

Orthogonal bioconjugation targeting cysteine-containing peptides and proteins using alkyl thianthrenium salts

Late-stage specific and selective diversifications of peptides and proteins performed at target residues under ambient conditions are recognized to be the most facile route to various and abundant conjugates. Herein, we report an orthogonal modification of cysteine residues using alkyl thianthreium salts, which proceeds with excellent chemoselectivity and compatibility under mild conditions, introducing a diverse array of functional structures. Crucially, multifaceted bioconjugation is achieved through clickable handles to incorporate structurally diverse functional molecules. This "two steps, one pot" bioconjugation method is successfully applied to label bovine serum albumin. Therefore, our technique is a versatile and powerful tool for late-stage orthogonal bioconjugation.

Self-Promoted Glycosylation of Carbamoylated Peptides on Solid Phase

Self-promoted glycosylations with trichloroacetimidate glycosyl donors are demonstrated on solid-phase-anchored peptides orthogonally deprotected and tosylcarbamoylated on the side-chains of cysteine and serine, respectively. The donor scope included glucosyl as well as mannosyl trichloroacetimidates, carrying benzyl, acetyl, or isopropylidene protecting groups. Isopropylidene groups were found to be removed under the acidic conditions used for release of the neoglycopeptides from the solid support, yielding neoglycopeptides with unprotected hydroxyl groups. Glycosylation of a peptide containing a carbamoylated tyrosine was attempted as well, but the desired neoglycopeptide could not be synthesized due to thermal instability of the carbamate.

Covalent Binding of Reactive Anhydride of Cantharidin to Biological Amines

Cantharidin is a terpenoid from coleoptera beetles. Cantharidin has been used to treat molluscum contagiosum and some types of tumors. Cantharidin is highly toxic, and cantharidin poisoning and fatal cases have been reported worldwide. The mechanisms underlying cantharidin-induced toxicity remain unclear. Cantharidin contains anhydride, which may react with biologic amines. This study aimed to examine the chemical reactivity of cantharidin toward nucleophiles and characterize adducts of cantharidin with biologic amines in vitro and in mice. Here two types of conjugates were formed in the incubation of cantharidin under physiologic conditions with free amino acids, a mimic peptide, or amine-containing compounds, respectively. Amide-type conjugates were produced by the binding of cantharidin anhydride with the primary amino group of biologic amines. Imide-type conjugates were generated from the dehydration and cyclization of amide-type conjugates. The structure of the conjugates was characterized by using high-resolution mass spectrometry. We introduced the 14N/15N and 79Br/81Br isotope signatures to confirm the formation of conjugates using L-(ε)15N-lysine, L-lysine-15N2, and bromine-tagged hydrazine, respectively. The structure of imide conjugate was also confirmed by nuclear magnetic resonance experiments. Furthermore, the amide and imide conjugates of cantharidin with amino acids or N-acetyl-lysine were detected in mouse liver and urine. Cantharidin was found to modify lysine residue proteins in mouse liver. Pan-cytochrome P450 inhibitor 1-aminobenzotriazole significantly increased the urine cantharidin-N-acetyl-lysine conjugates, whereas it decreased cantharidin metabolites. In summary, cantharidin anhydride can covalently bind to biologic amines nonenzymatically, which facilitates a better understanding of the role of nonenzymatic reactivity in cantharidin poisoning. SIGNIFICANCE STATEMENT: Anhydride moiety of cantharidin can covalently bind to the primary amino group of biological amines nonenzymatically. Amide and imide conjugates were generated after the covalent binding of cantharidin anhydride with the primary amino groups of amino acids, a mimic peptide, and protein lysine residues. The structure of conjugates was confirmed by 14N/15N and 79Br/81Br isotope signatures using isotope-tagged reagents and nuclear magnetic resonance experiments. This study will facilitate the understanding of the role of nonenzymatic reactivity in cantharidin poisoning.

Proline Analogues

Within the canonical repertoire of the amino acid involved in protein biogenesis, proline plays a unique role as an amino acid presenting a modified backbone rather than a side-chain. Chemical structures that mimic proline but introduce changes into its specific molecular features are defined as proline analogues. This review article summarizes the existing chemical, physicochemical, and biochemical knowledge about this peculiar family of structures. We group proline analogues from the following compounds: substituted prolines, unsaturated and fused structures, ring size homologues, heterocyclic, e.g., pseudoproline, and bridged proline-resembling structures. We overview (1) the occurrence of proline analogues in nature and their chemical synthesis, (2) physicochemical properties including ring conformation and cis/trans amide isomerization, (3) use in commercial drugs such as nirmatrelvir recently approved against COVID-19, (4) peptide and protein synthesis involving proline analogues, (5) specific opportunities created in peptide engineering, and (6) cases of protein engineering with the analogues. The review aims to provide a summary to anyone interested in using proline analogues in systems ranging from specific biochemical setups to complex biological systems.

Synthesis of N-Hydroxysuccinimide Esters, N-Acylsaccharins, and Activated Esters from Carboxylic Acids Using I2/PPh3

A method for the syntheses of isolable, active esters is described in which carboxylic acids are treated with triphenylphosphine, iodine, and triethylamine. Active esters accessible in this way include N-hydroxysuccinimide esters, N-hydroxyphthalimide esters (N-(acyloxy)phthalimides), N-acylsaccharins, pentafluorophenol esters, pentachlorophenol esters, N-hydroxybenzotriazole esters, and hexafluoro-2-propanol esters. The approach can be similarly applied toward the formation of N-acylsaccharins and N-acylimidazoles. The method is suitable for the formation of isolable active esters of aromatic and aliphatic activated acids as well as α-amino acid derivatives. These products are widely used reagents in organic synthesis, peptide synthesis, medicinal chemistry, and chemical biology (e.g., for bioconjugations). The method has broad substrate scope, uses simple and inexpensive reagents, avoids the use of carbodiimides or other coupling agents, and occurs at room temperature. Additionally, the diastereomers of compound Boc-Ala-NHCHPh are demonstrated to be distinguishable by 1H NMR (in DMSO-d6), allowing for a straightforward NMR method to establish the degree of racemization of activated esters of Boc-Ala or amide bond formations using Boc-Ala.

Lipid-derived electrophiles inhibit the function of membrane channels during ferroptosis

The therapeutic targeting of ferroptosis requires full understanding of the molecular mechanism of this regulated cell death pathway. While lipid-derived electrophiles (LDEs), including 4-hydroxy-2-nonenal (4-HNE), are important biomarkers of ferroptosis, a functional role for these highly reactive species in ferroptotic cell death execution has not been established. Here, through mechanistic characterization of LDE-detoxification impairment, we demonstrate that LDEs mediate altered protein function during ferroptosis. Applying live cell fluorescence imaging, we first identified that export of glutathione-LDE-adducts through multidrug resistance-associated protein (MRP) channels is inhibited following exposure to a panel of ferroptosis inducers (FINs) with different modes of action (type I-IV FINs erastin, RSL3, FIN56, and FINO2). This channel inhibition was recreated by both initiation of lipid peroxidation and treatment with 4-HNE. Importantly, treatment with radical-trapping antioxidants prevented impaired LDE-adduct export when working with both FINs and lipid peroxidation initiators but not 4-HNE, pinpointing LDEs as the cause of this inhibited MRP activity observed during ferroptosis. Our findings, when combined with reports of widespread LDE alkylation of key proteins following ferroptosis induction, including MRP1, set a precedent for LDEs as critical mediators of ferroptotic cell damage. Lipid hydroperoxide breakdown to form truncated phospholipids and LDEs may fully explain membrane permeabilization and modified protein function downstream of lipid peroxidation, offering a unified explanation of the molecular cell death mechanism of ferroptosis.

An Antibody-Drug Conjugate for Multiple Myeloma Prepared by Multi-Arm Linkers

First-line treatment of multiple myeloma, a prevalent blood cancer lacking a cure, using anti-CD38 daratumumab antibody and lenalidomide is often inadequate due to relapse and severe side effects. To enhance drug safety and efficacy, an antibody-drug conjugate, TE-1146, comprising six lenalidomide drug molecules site-specifically conjugated to a reconfigured daratumumab to deliver cytotoxic lenalidomide to tumor cells is developed. TE-1146 is prepared using the HighDAR platform, which employs i) a maleimide-containing "multi-arm linker" to conjugate multiple drug molecules creating a drug bundle, and ii) a designed peptide with a Zn2+-binding cysteine at the C-termini of a reconfigured daratumumab for site-specific drug bundle conjugation. It is shown that TE-1146 remains intact and effectively enters CD38-expressing tumor cells, releasing lenalidomide, leading to enhanced cell-killing effects compared to lenalidomide/daratumumab alone or their combination. This reveals the remarkable potency of lenalidomide once internalized by myeloma cells. TE-1146 precisely delivers lenalidomide to target CD38-overexpressing tumor cells. In contrast, lenalidomide without daratumumab cannot easily enter cells, whereas daratumumab without lenalidomide relies on Fc-dependent effector functions to kill tumor cells.

Peptide Stapling by Crosslinking Two Amines with α-Ketoaldehydes through Diverse Modified Glyoxal-Lysine Dimer Linkers

α-Ketoaldehydes play versatile roles in the ubiquitous natural processes of protein glycation. However, leveraging the reactivity of α-ketoaldehydes for biomedical applications has been challenging. Previously, the reactivity of α-ketoaldehydes with guanidine has been harnessed to design probes for labeling Arg residues on proteins in an aqueous medium. Herein, a highly effective, broadly applicable, and operationally simple protocol for stapling native peptides by crosslinking two amino groups through diverse imidazolium linkers with various α-ketoaldehyde reagents is described. The use of hexafluoroisopropanol as a solvent facilitates rapid and clean reactions under mild conditions and enables unique selectivity for Lys over Arg. The naturally occurring GOLD/MOLD linkers have been expanded to encompass a wide range of modified glyoxal-lysine dimer (OLD) linkers. In a proof-of-concept trial, these modular stapling reactions enabled a convenient two-round strategy to streamline the structure-activity relationship (SAR) study of the wasp venom peptide anoplin, leading to enhanced biological activities.

A pyridinium-based strategy for lysine-selective protein modification and chemoproteomic profiling in live cells

Protein active states are dynamically regulated by various modifications; thus, endogenous protein modification is an important tool for understanding protein functions and networks in complicated biological systems. Here we developed a new pyridinium-based approach to label lysine residues under physiological conditions that is low-toxicity, efficient, and lysine-selective. Furthermore, we performed a large-scale analysis of the ∼70% lysine-selective proteome in MCF-7 cells using activity-based protein profiling (ABPP). We quantifically assessed 1216 lysine-labeled peptides in cell lysates and identified 386 modified lysine sites including 43 mitochondrial-localized proteins in live MCF-7 cells. Labeled proteins significantly preferred the mitochondria. This pyridinium-based methodology demonstrates the importance of analyzing endogenous proteins under native conditions and provides a robust chemical strategy utilizing either lysine-selective protein labeling or spatiotemporal profiling in a living system.

Metal-free functionalization of tyrosine residues in short peptides and study of the morphological alterations

An efficient functionalization of tyrosine residues in phenolic regions is achieved under metal-free conditions. The strategy involves the conversion of a tyrosine residue to 4-amino phenylalanine or 4-amino-3-methoxy phenylalanine in short peptides through a controlled oxidative dearomatization. This transformation is achieved in one pot with good yields and excellent regioselectivity. Consequently, the self-assembly of the peptide compounds has been studied at the nanoscopic level before and after functionalization. The results suggest that the peptide derivatives comprising amide groups promote intermolecular H-bonding interactions and the difference in -OH and -NH2 functional groups is found to be responsible for the morphological changes. Morphological transitions from 1D nanowires to 2D nanosheets were observed during functional group modification.

Synthesis of carbon nanotubes-chitosan nanocomposite and immunosensor fabrication for myoglobin detection: An acute myocardial infarction biomarker

The use of single-walled carbon nanotubes (SWCNTs) in biomedical applications is limited due to their inability to disperse in aqueous solutions. In this study, dispersed -COOH functionalized CNTs with N-succinylated chitosan (CS), greatly increasing the water solubility of CNTs and forming a uniformly dispersed nanocomposite solution of CNTs@CS. Coupling reagent EDC/NHS was used as a linker with the -COOH groups present on the N-succinylated chitosan which significantly improved the affinity of the CNTs for biomolecules. Myoglobin (Mb) is a promising biomarker for the precise assessment of cardiovascular risk, type 2 diabetes, metabolic syndrome, hypertension and several types of cancer. A high level of Mb can be used to diagnose the mentioned pathogenic diseases. The CNTs@CS-FET demonstrates superior sensing performance for Mb antigen fortified in buffer, with a wide linear range of 1 to 4000 ng/mL. The detection limit of the developed Mb immunosensor was estimated to be 4.2 ng/mL. The novel CNTs@CS-FET immunosensor demonstrates remarkable capability in detecting Mb without being affected by interferences from nonspecific antigens. Mb spiked serum showed a recovery rate of 100.262 to 118.55 % indicating great promise for Mb detection in clinical samples. The experimental results confirmed that the CNTs@CS-FET immunosensor had excellent selectivity, reproducibility and storage stability.

Advancing protein therapeutics through proximity-induced chemistry

Recent years have seen a remarkable growth in the field of protein-based medical treatments. Nevertheless, concerns have arisen regarding the cytotoxicity limitations, low affinity, potential immunogenicity, low stability, and challenges to modify these proteins. To overcome these obstacles, proximity-induced chemistry has emerged as a next-generation strategy for advancing protein therapeutics. This method allows site-specific modification of proteins with therapeutic agents, improving their effectiveness without extensive engineering. In addition, this innovative approach enables spatial control of the reaction based on proximity, facilitating the formation of irreversible covalent bonds between therapeutic proteins and their targets. This capability becomes particularly valuable in addressing challenges such as the low affinity frequently encountered between therapeutic proteins and their targets, as well as the limited availability of small molecules for specific protein targets. As a result, proximity-induced chemistry is reshaping the field of protein drug preparation and propelling the revolution in novel protein therapeutics.

Enhancing Photothermal/Photodynamic Therapy for Glioblastoma by Tumor Hypoxia Alleviation and Heat Shock Protein Inhibition Using IR820-Conjugated Reduced Graphene Oxide Quantum Dots

We use low-molecular-weight branched polyethylenimine (PEI) to produce cytocompatible reduced graphene oxide quantum dots (rGOQD) as a photothermal agent and covalently bind it with the photosensitizer IR-820. The rGOQD/IR820 shows high photothermal conversion efficiency and produces reactive oxygen species (ROS) after irradiation with near-infrared (NIR) light for photothermal/photodynamic therapy (PTT/PDT). To improve suspension stability, rGOQD/IR820 was PEGylated by anchoring with the DSPE hydrophobic tails in DSPE-PEG-Mal, leaving the maleimide (Mal) end group for covalent binding with manganese dioxide/bovine serum albumin (MnO2/BSA) and targeting ligand cell-penetrating peptide (CPP) to synthesize rGOQD/IR820/MnO2/CPP. As MnO2 can react with intracellular hydrogen peroxide to produce oxygen for alleviating the hypoxia condition in the acidic tumor microenvironment, the efficacy of PDT could be enhanced by generating more cytotoxic ROS with NIR light. Furthermore, quercetin (Q) was loaded to rGOQD through π-π interaction, which can be released in the endosomes and act as an inhibitor of heat shock protein 70 (HSP70). This sensitizes tumor cells to thermal stress and increases the efficacy of mild-temperature PTT with NIR irradiation. By simultaneously incorporating the HSP70 inhibitor (Q) and the in situ hypoxia alleviating agent (MnO2), the rGOQD/IR820/MnO2/Q/CPP can overcome the limitation of PTT/PDT and enhance the efficacy of targeted phototherapy in vitro. From in vivo study with an orthotopic brain tumor model, rGOQD/IR820/MnO2/Q/CPP administered through tail vein injection can cross the blood-brain barrier and accumulate in the intracranial tumor, after which NIR laser light irradiation can shrink the tumor and prolong the survival times of animals by simultaneously enhancing the efficacy of PTT/PDT to treat glioblastoma.

N-Terminal-Specific Dual Modification of Peptides through Copper-Catalyzed [3+2] Cycloaddition

Site-specific introduction of multiple components into peptides is greatly needed for the preparation of densely functionalized and structurally uniform peptides. In this regard, N-terminal-specific peptide modification is attractive, but it can be difficult due to the presence of highly nucleophilic lysine ϵ-amine. In this work, we developed a method for the N-terminal-specific dual modification of peptides through a three-component [3+2] cycloaddition with aldehydes and maleimides under mild copper catalysis. This approach enables exclusive functionalization at the glycine N-terminus of iminopeptides, regardless of the presence of lysine ϵ-amine, thus affording the cycloadducts in excellent yields. Tolerating a broad range of functional groups and molecules, the present method provides the opportunity to rapidly construct doubly functionalized peptides using readily accessible aldehyde and maleimide modules.

Formaldehyde-Mediated Hydride Liberation of Alkylamines for Intermolecular Reactions in Hexafluoroisopropanol

The ability of alkylamines to spontaneously liberate hydride ions is typically restrained, except under specific intramolecular reaction settings. Herein, we demonstrate that this reactivity can be unlocked through simple treatment with formaldehyde in hexafluoroisopropanol (HFIP) solvent, thereby enabling various intermolecular hydride transfer reactions of alkylamines under mild conditions. Besides transformations of small molecules, these reactions enable unique late-stage modification of complex peptides. Mechanistic investigations uncover that the key to these intermolecular hydride transfer processes lies in the accommodating conformation of solvent-mediated macrocyclic transition states, where the aggregates of HFIP molecules act as dexterous proton shuttles. Importantly, negative hyperconjugation between the lone electron pair of nitrogen and the antibonding orbital of amine's α C-H bond plays a critical role in the C-H activation, promoting its hydride liberation.

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.

Recent Advances in Photoinduced Modification of Amino Acids, Peptides, and Proteins

The chemical modification of biopolymers like peptides and proteins is a key technology to access vaccines and pharmaceuticals. Similarly, the tunable derivatization of individual amino acids is important as they are key building blocks of biomolecules, bioactive natural products, synthetic polymers, and innovative materials. The high diversity of functional groups present in amino acid-based molecules represents a significant challenge for their selective derivatization Recently, visible light-mediated transformations have emerged as a powerful strategy for achieving chemoselective biomolecule modification. This technique offers numerous advantages over other methods, including a higher selectivity, mild reaction conditions and high functional-group tolerance. This review provides an overview of the most recent methods covering the photoinduced modification for single amino acids and site-selective functionalization in peptides and proteins under mild and even biocompatible conditions. Future challenges and perspectives are discussed beyond the diverse types of photocatalytic transformations that are currently available.

Backbone-enabled modification of peptides with benzoquinone via palladium-catalyzed δ-C(sp2)-H functionalization

Backbone-enabled site-selective modification of peptides with benzoquinone via Pd-catalyzed δ-C(sp2)-H functionalization has been achieved. The amide groups of peptides serve as internal directional groups, facilitating C-H functionalization through a kinetically less favored six-membered palladacycle. This methodology presents novel opportunities for the late-stage site-selective diversification of peptides.

Antibody-decorated chitosan-iodoacetamide-coated nanocarriers for the potential delivery of doxorubicin to breast cancer cells

Using an active targeting approach of chemotherapeutics-loaded nanocarriers (NCs) with monoclonal antibodies is a potential strategy to improve the specificity of the delivery systems and reduce adverse reactions of chemotherapeutic drugs. Specific targeting of the human epidermal growth factor receptor-2 (HER-2), expressed excessively in HER-2-positive breast cancer cells, can be achieved by conjugating NCs with an anti-HER-2 monoclonal antibody. We constructed trastuzumab-conjugated chitosan iodoacetamide-coated NCs containing doxorubicin (Tras-Dox-CHI-IA-NCs) as a tumor-targeted drug delivery system, during the study. Chitosan-iodoacetamide (CHI-IA) was synthesized and utilized to prepare trastuzumab-conjugated NCs (Tras-NCs). The morphology, physicochemical properties, drug loading, drug release, and biological activities of the NCs were elucidated. The Tras-NCs were spherical, with a particle size of approximately 76 nm, and had a positive zeta potential; after incorporating the drug, the size of the Tras-NC increased. A prolonged, 24-h drug release from the NCs was achieved. The Tras-NCs exhibited high cellular accumulation and significantly higher antitumor activity against HER-2-positive breast cancer cells than the unconjugated NCs and the drug solution. Therefore, Tras-Dox-CHI-IA-NCs could be a promising nanocarrier for HER-2-positive breast cancer.

Silicon-Containing Thiol-Specific Bioconjugating Reagent

A new bioconjugation reagent containing silicon has been developed for the selective reaction with thiols. The inclusion of silicon significantly improves chemoselectivity and suppresses retro processes, thereby exceeding the capabilities of traditional reagents. The method is versatile and compatible with a broad range of thiols and unsaturated carbonyl compounds and yields moderate to high results. These reactions can be conducted under biocompatible conditions, thereby making them suitable for protein bioconjugation. The resulting conjugates display good stability in the presence of various biomolecules, which suggests their potential application for the synthesis of antibody-drug conjugates. Furthermore, the presence of a silicon moiety within the conjugated products opens up new avenues for drug release and bridging inorganics with other disciplines. This new class of silicon-containing thiol-specific bioconjugation reagents has significant implications for researchers working in bioanalytical science and medicinal chemistry and leads to innovative opportunities for advancing the field of bioconjugation research and medicinal chemistry.

Metal-Free 1,3-Boronate Rearrangement to Ketones Driven by Visible Light

Boronate rearrangements, such as the Matteson and Petasis reactions, are valuable metal-free reactions for the transfer of the carbo group on boron to intramolecular electrophilic sites. However, only highly reactive electrophiles are suitable, and ketones are too inactive for those boronate rearrangements due to the high energy barriers. We disclose here the 1,3-boronate rearrangement to ketones, for which a high energy barrier (44.9 kcal/mol) is prohibitory for thermal reactions in the ground state. The reaction is enabled by the key keto-enol-boronate bidentate complex formation in situ, which absorbs visible light to reach the excited state for the chemoselective 1,3-boronate rearrangement to ketones. Experimental and computational investigations exclude free radical intermediates from organoboronates. The aryl, alkenyl, and alkyl boronic acids react with various 1,3-diketones driven by visible light irradiation to construct structurally diverse β-keto tertiary alcohols under metal-free conditions. The reaction demonstrates substrate diversity with 58 examples, yields up to 98 %, and it is suitable for gram-scale synthesis.

SpSrtA-Catalyzed Isopeptide Ligation on Lysine Residues

Sortase-mediated ligation (SML) is widely used for protein bioconjugation. However, the sortase used in this strategy typically recognizes only the N-terminal oligoglycine, which is absent in most natural proteins. To broaden the spectrum of substrates compatible with SML, we focus on a novel sortase, sortase A from Streptococcus pneumoniae (SpSrtA), known for its expanded substrate specificity (N-terminal glycine, alanine, and serine). We present the first evidence showing that the reported SpSrtA mutant (SpSrtA*) can modify lysine residues in itself and other proteins. The modification sites of SpSrtA* were identified through LC-MS/MS analysis. Moreover, we discovered an optimal lysine-containing peptide tag by fusing it onto sfGFP, resulting in a labeling efficiency of 57%. Inspired by this, we applied the method to modify proteins on microorganism surfaces up to 13.5-fold. To enhance labeling efficiency, we fused the SpSrtA* onto a surface protein and achieved a 2.64-fold improvement. We further developed a high-throughput yeast display screening method for the directed evolution of SpSrtA*, achieving a 10-fold improvement in the labeling efficiency of this surface protein. Our study provides a novel strategy for modifying the lysine residues that will be a powerful addition to the protein bioconjugation toolbox.

Affinity-Directed Site-Specific Protein Labeling and Its Application to Antibody-Drug Conjugates

Chemically modified proteins have diverse applications; however, conventional chemo-selective methods often yield heterogeneously labeled products. To address this limitation, site-specific protein labeling holds significant potential, driving extensive research in this area. Nevertheless, site-specific modification of native proteins remains challenging owing to the complexity of their functional groups. Therefore, a method for site-selective labeling of intact proteins is aimed to design. In this study, a novel approach to traceless affinity-directed intact protein labeling is established, which leverages small binding proteins and genetic code expansion technology. By applying this method, a site-specific antibody labeling with a drug, which leads to the production of highly effective antibody-drug conjugates specifically targeting breast cancer cell lines is achieved. This approach enables traceless conjugation of intact target proteins, which is a critical advantage in pharmaceutical applications. Furthermore, small helical binding proteins can be easily engineered for various target proteins, thereby expanding their potential applications in diverse fields. This innovative approach represents a significant advancement in site-specific modification of native proteins, including antibodies. It also bears immense potential for facilitating the development of therapeutic agents for various diseases.

Bioconjugation Techniques for Enhancing Stability and Targeting Efficiency of Protein and Peptide Therapeutics

Bioconjugation techniques have emerged as powerful tools for enhancing the stability and targeting efficiency of protein and peptide therapeutics. This review provides a comprehensive analysis of the various bioconjugation strategies employed in the field. The introduction highlights the significance of bioconjugation techniques in addressing stability and targeting challenges associated with protein and peptide-based drugs. Chemical and enzymatic bioconjugation methods are discussed, along with crosslinking strategies for covalent attachment and site-specific conjugation approaches. The role of bioconjugation in improving stability profiles is explored, showcasing case studies that demonstrate successful stability enhancement. Furthermore, bioconjugation techniques for ligand attachment and targeting are presented, accompanied by examples of targeted protein and peptide therapeutics. The review also covers bioconjugation approaches for prolonging circulation and controlled release, focusing on strategies to extend half-life, reduce clearance, and design-controlled release systems. Analytical characterization techniques for bioconjugates, including the evaluation of conjugation efficiency, stability, and assessment of biological activity and targeting efficiency, are thoroughly examined. In vivo considerations and clinical applications of bioconjugated protein and peptide therapeutics, including pharmacokinetic and pharmacodynamic considerations, as well as preclinical and clinical developments, are discussed. Finally, the review concludes with an overview of future perspectives, emphasizing the potential for novel conjugation methods and advanced targeting strategies to further enhance the stability and targeting efficiency of protein and peptide therapeutics.