Probing N-Glycan Functions in Human Interleukin-17A Based on Chemically Synthesized Homogeneous Glycoforms

A Versatile Method for Site-Specific Chemical Installation of Aromatic Posttranslational Modification Analogs into Proteins

Posttranslational modifications (PTMs) of proteins play central roles in regulating the protein structure, interactome, and functions. A notable modification site is the aromatic side chain of Tyr, which undergoes modifications such as phosphorylation and nitration. Despite the biological and physiological importance of Tyr-PTMs, our current understanding of the mechanisms by which these modifications contribute to human health and disease remains incomplete. This knowledge gap arises from the absence of natural amino acids that can mimic these PTMs and the lack of synthetic tools for the site-specific introduction of aromatic PTMs into proteins. Herein, we describe a facile method for the site-specific chemical installation of aromatic PTMs into proteins through palladium-mediated S-C(sp2) bond formation under ambient conditions. We demonstrate the incorporation of novel PTMs such as Tyr-nitration and phosphorylation analogs to synthetic and recombinantly expressed Cys-containing peptides and proteins within minutes and in good yields. To demonstrate the versatility of our approach, we employed it to prepare 10 site-specifically modified proteins, including nitrated and phosphorylated analogs of Myc and Max proteins. Furthermore, we prepared a focused library of site-specifically nitrated and phosphorylated α-synuclein (α-Syn) protein, which enabled, for the first time, deciphering the role of these competing modifications in regulating α-Syn conformation aggregation in vitro. Our strategy offers advantages over synthetic or semisynthetic approaches, as it enables rapid and selective transfer of rarely explored aromatic PTMs into recombinant proteins, thus facilitating the generation of novel libraries of homogeneous posttranslationally modified proteins for biomarker discovery, mechanistic studies, and drug discovery.

Protein desulfurization and deselenization

Methods enabling the dechalcogenation of thiols or selenols have been investigated and developed for a long time in fields of research as diverse as the study of prebiotic chemistry, the engineering of fuel processing techniques, the study of biomolecule structures and function or the chemical synthesis of biomolecules. The dechalcogenation of thiol or selenol amino acids is nowadays a particularly flourishing area of research for being a pillar of modern chemical protein synthesis, when used in combination with thiol or selenol-based chemoselective peptide ligation chemistries. This review offers a comprehensive and scholarly overview of the field, emphasizing emerging trends and providing a detailed and critical mechanistic discussion of the dechalcogenation methods developed so far. Taking advantage of recently published reports, it also clarifies some unexpected desulfurization reactions that were observed in the past and for which no explanation was provided at the time. Additionally, the review includes a discussion on principal desulfurization methods within the framework of newly introduced green chemistry metrics and toolkits, providing a well-rounded exploration of the subject.

Chemical Synthesis of Interleukin-6 for Mirror-Image Screening

Interleukin-6 (IL-6), a multifunctional cytokine, is an attractive therapeutic target for immunological and inflammatory diseases. We investigated the chemical synthesis of IL-6 and its enantiomer (d-IL-6) using a sequential N-to-C native chemical ligation strategy from six peptide segments. Solubilizing Trt-K10 tags improved the intermediate solubility and served as protecting groups during the metal-free desulfurization to facilitate the synthesis of full-length IL-6 protein. Synthetic l-IL-6 and recombinant IL-6 exhibited nearly identical structural and binding properties. The symmetrical binding property of d-IL-6 was also demonstrated by functional analysis using IL-6-binding peptides. The resulting functional d-IL-6 was employed to screen a phage-displayed antibody fragment library, leading to the identification of several d-IL-6-binding single-domain antibodies. This work will contribute to the development of novel, potent IL-6 inhibitors without the adverse effects of undesired immune activation.

Establishing a Cell-Free Glycoprotein Synthesis System for Enzymatic N-GlcNAcylation

N-linked glycosylation plays a key role in the efficacy of many therapeutic proteins. One limitation to the bacterial glycoengineering of human N-linked glycans is the difficulty of installing a single N-acetylglucosamine (GlcNAc), the reducing end sugar of many human-type glycans, onto asparagine in a single step (N-GlcNAcylation). Here, we develop an in vitro method for N-GlcNAcylating proteins using the oligosaccharyltransferase PglB from Campylobacter jejuni. We use cell-free protein synthesis (CFPS) to test promiscuous PglB variants previously reported in the literature for the ability to produce N-GlcNAc and successfully determine that PglB with an N311V mutation (PglBN311V) exhibits increased GlcNAc transferase activity relative to the wild-type enzyme. We then improve the transfer efficiency by producing CFPS extracts enriched with PglBN311V and further optimize the reaction conditions, achieving a 98.6 ± 0.5% glycosylation efficiency. We anticipate this method will expand the glycoengineering toolbox for therapeutic research and biomanufacturing.

Investigation of N-Glycan Functions in Receptor for Advanced Glycation End Products V Domain through Chemical Glycoprotein Synthesis

The receptor for advanced glycation end products (RAGE) plays a crucial role in inflammation-related pathways and various chronic diseases. Despite the recognized significance of N-glycosylation in the ligand-binding V domain (VD) of RAGE, a comprehensive understanding of the site-activity and structure-activity relationships is lacking due to the challenges in obtaining homogeneous glycoprotein samples through biological expression. Here, we combined chemical and chemoenzymatic approaches to synthesize RAGE-VD and its congeners with Asn3-glycosylation by incorporating precise N-glycan structures. Evaluation of these samples revealed that, in comparison to other RAGE-VD forms, α2,6-sialylated N-glycosylation at the Asn3 site results in more potent inhibition of HMGB1-induced nuclear factor-κB (NF-κB) expression in RAGE-overexpressing cells. Hydrogen/deuterium exchange-mass spectrum analysis revealed a sialylated RAGE-VD-induced interaction region within HMGB1. Conversely, Asn3 N-glycosylation in VD has negligible effects on RAGE-VD/S100B interactions. This study established an approach for accessing homogeneously glycosylated RAGE-VD and explored the modulatory effects of N-glycosylation on the interactions between RAGE-VD and its ligand proteins.

Rab37 mediates trafficking and membrane presentation of PD-1 to sustain T cell exhaustion in lung cancer

BACKGROUND

Programmed cell death protein 1 (PD-1) is an immune checkpoint receptor expressed on the surface of T cells. High expression of PD-1 leads to T-cell dysfunction in the tumor microenvironment (TME). However, the mechanism of intracellular trafficking and plasma membrane presentation of PD-1 remains unclear.

METHODS

Multiple databases of lung cancer patients were integratively analyzed to screen Rab proteins and potential immune-related signaling pathways. Imaging and various biochemical assays were performed in Jurkat T cells, splenocytes, and human peripheral blood mononuclear cells (PBMCs). Rab37 knockout mice and specimens of lung cancer patients were used to validate the concept.

RESULTS

Here, we identify novel mechanisms of intracellular trafficking and plasma membrane presentation of PD-1 mediated by Rab37 small GTPase to sustain T cell exhaustion, thereby leading to poor patient outcome. PD-1 colocalized with Rab37-specific vesicles of T cells in a GTP-dependent manner whereby Rab37 mediated dynamic trafficking and membrane presentation of PD-1. However, glycosylation mutant PD-1 delayed cargo recruitment to the Rab37 vesicles, thus stalling membrane presentation. Notably, T cell proliferation and activity were upregulated in tumor-infiltrating T cells from the tumor-bearing Rab37 knockout mice compared to those from wild type. Clinically, the multiplex immunofluorescence-immunohistochemical assay indicated that patients with high Rab37+/PD-1+/TIM3+/CD8+ tumor infiltrating T cell profile correlated with advanced tumor stages and poor overall survival. Moreover, human PBMCs from patients demonstrated high expression of Rab37, which positively correlated with elevated levels of PD-1+ and TIM3+ in CD8+ T cells exhibiting reduced tumoricidal activity.

CONCLUSIONS

Our results provide the first evidence that Rab37 small GTPase mediates trafficking and membrane presentation of PD-1 to sustain T cell exhaustion, and the tumor promoting function of Rab37/PD-1 axis in T cells of TME in lung cancer. The expression profile of Rab37high/PD-1high/TIM3high in tumor-infiltrating CD8+ T cells is a biomarker for poor prognosis in lung cancer patients.

Chemical Synthesis Creates Single Glycoforms of the Ectodomain of Herpes Simplex Virus-1 Glycoprotein D

Herpes simplex virus-1 (HSV-1) utilizes multiple viral surface glycoproteins to trigger virus entry and fusion. Among these glycoproteins, glycoprotein D (gD) functions as a receptor-binding protein, which makes it an attractive target for the development of vaccines against HSV-1 infection. Several recombinant gD subunit vaccines have been investigated in both preclinical and clinical phases with varying degrees of success. It is fundamentally critical to explore the functions of gD glycans. In light of this, we report an efficient synthetic platform to construct glycosylated gDs bearing homogeneous glycans at N94 and N121. The oligosaccharides were prepared by enzymatic synthesis and conjugated to peptidyl sectors. The glycoproteins were constructed via a combination of 7-(piperazin-1-yl)-2-(methyl)quinolinyl (PPZQ)-assisted expressed protein ligation and β-mercapto amino acid-assisted-desulfurization strategies. Biological studies showed that synthetic gDs exhibited potent in vivo activity in mice.

Deciphering the Role of the Ser-Phosphorylation Pattern on the DNA-Binding Activity of Max Transcription Factor Using Chemical Protein Synthesis

The chemical synthesis of site-specifically modified transcription factors (TFs) is a powerful method to investigate how post-translational modifications (PTMs) influence TF-DNA interactions and impact gene expression. Among these TFs, Max plays a pivotal role in controlling the expression of 15 % of the genome. The activity of Max is regulated by PTMs; Ser-phosphorylation at the N-terminus is considered one of the key regulatory mechanisms. In this study, we developed a practical synthetic strategy to prepare homogeneous full-length Max for the first time, to explore the impact of Max phosphorylation. We prepared a focused library of eight Max variants, with distinct modification patterns, including mono-phosphorylated, and doubly phosphorylated analogues at Ser2/Ser11 as well as fluorescently labeled variants through native chemical ligation. Through comprehensive DNA binding analyses, we discovered that the phosphorylation position plays a crucial role in the DNA-binding activity of Max. Furthermore, in vitro high-throughput analysis using DNA microarrays revealed that the N-terminus phosphorylation pattern does not interfere with the DNA sequence specificity of Max. Our work provides insights into the regulatory role of Max's phosphorylation on the DNA interactions and sequence specificity, shedding light on how PTMs influence TF function.

N,O-Benzylidene Acetal Dipeptides (NBDs) Enable the Synthesis of Difficult Peptides via a Kinked Backbone Strategy

Proteins with highly hydrophobic regions or aggregation-prone sequences are typically difficult targets for chemical synthesis at the current stage, as obtaining such type of peptides via solid-phase peptide synthesis requires sophisticated operations. Herein, we report N,O-benzylidene acetal dipeptides (NBDs) as robust and effective building blocks to allow the direct synthesis of difficult peptides and proteins via a kinked backbone strategy. The effectiveness and easy accessibility of NBDs have been well demonstrated in our chemical syntheses of various challenging peptides and proteins, including chemokine, therapeutic hormones, histone, and glycosylated erythropoietin.

Recent advances on the synthesis of N-linked glycoprotein for the elucidation of glycan functions

Glycoproteins play roles in many biological events, while, the glycan structure-function relationship has remained to be studied. In order to understand glycan function, homogeneous glycoproteins have been synthesized. This review introduced recent progress of their synthetic approaches.

Chemical Synthesis of Bioactive Proteins

Nature has developed a plethora of protein machinery to operate and maintain nearly every task of cellular life. These processes are tightly regulated via post-expression modifications-transformations that modulate intracellular protein synthesis, folding, and activation. Methods to prepare homogeneously and precisely modified proteins are essential to probe their function and design new bioactive modalities. Synthetic chemistry has contributed remarkably to protein science by allowing the preparation of novel biomacromolecules that are often challenging or impractical to prepare via common biological means. The ability to chemically build and precisely modify proteins has enabled the production of new molecules with novel physicochemical properties and programmed activity for biomedical research, diagnostic, and therapeutic applications. This minireview summarizes recent developments in chemical protein synthesis to produce bioactive proteins, with emphasis on novel analogs with promising in vitro and in vivo activity.

Total synthesis of interleukin-2 via a tunable backbone modification strategy

Chemical synthesis of hydrophobic proteins presents a formidable task as they are often difficultly achieved via peptide synthesis, purification, and peptide ligation. Thus, peptide solubilizing strategies are needed to integrate with peptide ligation to achieve protein total synthesis. Herein, we report a tunable backbone modification strategy, taking advantage of the tunable stability of the Cys/Pen ligation intermediate, which allows for readily introducing a solubilizing tag for both peptide purification and ligation processes. The effectiveness of this strategy was demonstrated by the chemical synthesis of interleukin-2.

N-Glycan Engineering: Constructing the N-GlcNAc Stump

N-Glycosylation is often essential for the structure and function of proteins. However, N-glycosylated proteins from natural sources exhibit considerable heterogeneity in the appended oligosaccharides, bringing daunting challenges to corresponding basic research and therapeutic applications. To address this issue, various synthetic, enzymatic, and chemoenzymatic approaches have been elegantly designed. Utilizing the endoglycosidase-catalyzed transglycosylation method, a single N-acetylglucosamine (N-GlcNAc, analogous to a tree stump) on proteins can be converted to various homogeneous N-glycosylated forms, thereby becoming the focus of research efforts. In this concept article, we briefly introduce the methods that allow the generation of N-GlcNAc and its close analogues on proteins and peptides and highlight the current challenges and opportunities the scientific community is facing.

Identification of the effect of N-glycan modification and its sialylation on proteolytic stability and glucose-stabilizing activity of glucagon-like peptide 1 by site-directed enzymatic glycosylation

In this study, an approach to prepare long-acting glucagon-like peptide 1 (GLP-1) by site-directed enzymatic glycosylation with homogeneous biantennary complex-type N-glycan has been developed. All the N-glycan-modified GLP-1 analogues preserved an unchanged secondary structure. The glycosylated GLP-1 analogues with sialyl complex-type N-glycan modified at Asn26 and Asn34 exhibited a 36.7- and 24.0-fold in vitro half-life respectively when incubated with dipeptidyl peptidase-IV (DPP-IV), and 25.0- and 13.9-fold respectively when incubated with mouse serum. Compared to native GLP-1, both glycosylated GLP-1 analogues modified at Asn34 by asialyl and sialyl N-glycan demonstrated lower maximum blood glucose levels, as well as more rapid and more persistent glucose-stabilizing capability in type 2 diabetic db/db mice. Our results indicated that the selection of an appropriate position (to avoid hindering the peptide-receptor binding) is crucial for N-glycan modification and its sialylation to improve the therapeutic properties of the modified peptides. The information learned would facilitate future design of therapeutic glycopeptides/glycoproteins with N-glycan to achieve enhanced pharmacological properties.

Ligation Embedding Aggregation Disruptor Strategy Enables the Chemical Synthesis of PD-1 Immunoglobulin and Extracellular Domains

Chemical synthesis of proteins with aggregable or colloidal peptide segments presents a formidable task, as such peptides prove to be difficult for both solid-phase peptide synthesis and peptide ligation. To address this issue, we have developed ligation embedding aggregation disruptor (LEAD) as an effective strategy for the chemical synthesis of difficult-to-obtain proteins. The N,O/S-benzylidene acetals generated from Ser/Thr ligation and Cys/Pen ligation are found to effectively disrupt peptide aggregation, and they can be carried for sequential ligations toward protein synthesis. The effectiveness and generality of this strategy have been demonstrated with total syntheses of programmed cell death protein 1 immunoglobulin like V-type domain and extracellular domain.

Discovery of an Oral, Rule of 5 Compliant, Interleukin 17A Protein-Protein Interaction Modulator for the Potential Treatment of Psoriasis and Other Inflammatory Diseases

Interleukin 17A (IL-17A) is an interleukin cytokine whose dysregulation is implicated in autoimmune disorders such as psoriasis, and monoclonal antibodies against the IL-17A pathway are now well-established and very effective treatments. This article outlines the work that led to the identification of 23 as an oral, small-molecule protein-protein interaction modulator (PPIm) clinical development candidate. Protein crystallography provided knowledge of the key binding interactions between small-molecule ligands and the IL-17A dimer, and this helped in the multiparameter optimization toward identifying an orally bioavailable, Rule of 5 compliant PPIm of IL-17A. Overlap of early ligands led to a series of benzhydrylglycine-containing compounds that allowed the identification of dimethylpyrazole as a key substituent that gave PPIm with oral bioavailability. Exploration of the amino acid portion of the structure then led to dicyclopropylalanine as a group that gave potent and metabolically stable compounds, including the development candidate 23.

Design and Synthesis of Glycosylated Cholera Toxin B Subunit as a Tracer of Glycoprotein Trafficking in Organelles of Living Cells

Glycosylation of proteins is known to be essential for changing biological activity and stability of glycoproteins on the cell surfaces and in body fluids. Delivering of homogeneous glycoproteins into the endoplasmic reticulum (ER) and the Golgi apparatus would enable us to investigate the function of asparagine-linked (N-) glycans in the organelles. In this work, we designed and synthesized an intentionally glycosylated cholera toxin B-subunit (CTB) to be transported to the organelles of mammalian cells. The heptasaccharide, the intermediate structure of various complex-type N-glycans, was introduced to the CTB. The synthesized monomeric glycosyl-CTB successfully entered mammalian cells and was transported to the Golgi and the ER, suggesting the potential use of synthetic CTB to deliver and investigate the functions of homogeneous N-glycans in specific organelles of living cells.

Recent Chemical and Chemoenzymatic Strategies to Complex-Type N-Glycans

Glycosylation is one of the major forms of protein post-translational modification. N-glycans attached to proteins by covalent bonds play an indispensable role in intercellular interaction and immune function. In human bodies, most of the cell surface glycoproteins and secreted glycopeptides are modified with complex-type N-glycans. Thus, for analytical or medicinal purposes, efficient and universal methods to provide homogeneous complex-type N-glycans have been an urgent need. Despite the extremely complicated structures, tremendous progress in the synthesis of N-glycans has been achieved. On one hand, chemical strategies are shown to be effective to prepare core oligosaccharides of N-glycans by focusing on stereoselective glycosylations such as β-mannosylation and α-sialylation, as well as the methodology of the N-glycan assembly. On the other hand, chemoenzymatic strategies have also become increasingly powerful in recent years. This review attempts to highlight the very recent advancements in chemical and chemoenzymatic strategies for eukaryotic complex-type N-glycans.

Automated Peptide Synthesizers and Glycoprotein Synthesis

The development and application of commercially available automated peptide synthesizers has played an essential role in almost all areas of peptide and protein research. Recent advances in peptide synthesis method and solid-phase chemistry provide new opportunities for optimizing synthetic efficiency of peptide synthesizers. The efforts in this direction have led to the successful preparation of peptides up to more than 150 amino acid residues in length. Such success is particularly useful for addressing the challenges associated with the chemical synthesis of glycoproteins. The purpose of this review is to provide a brief overview of the evolution of peptide synthesizer and glycoprotein synthesis. The discussions in this article include the principles underlying the representative synthesizers, the strengths and weaknesses of different synthesizers in light of their principles, and how to further improve the applicability of peptide synthesizers in glycoprotein synthesis.

Synthetic Thiol and Selenol Derived Amino Acids for Expanding the Scope of Chemical Protein Synthesis

Cells employ post-translational modifications (PTMs) as key mechanisms to expand proteome diversity beyond the inherent limitations of a concise genome. The ability to incorporate post-translationally modified amino acids into protein targets via chemical ligation of peptide fragments has enabled the access to homogeneous proteins bearing discrete PTM patterns and empowered functional elucidation of individual modification sites. Native chemical ligation (NCL) represents a powerful and robust means for convergent assembly of two homogeneous, unprotected peptides bearing an N-terminal cysteine residue and a C-terminal thioester, respectively. The subsequent discovery that protein cysteine residues can be chemoselectively desulfurized to alanine has ignited tremendous interest in preparing unnatural thiol-derived variants of proteogenic amino acids for chemical protein synthesis following the ligation-desulfurization logic. Recently, the 21st amino acid selenocysteine, together with other selenyl derivatives of amino acids, have been shown to facilitate ultrafast ligation with peptidyl selenoesters, while the advancement in deselenization chemistry has provided reliable bio-orthogonality to PTMs and other amino acids. The combination of these ligation techniques and desulfurization/deselenization chemistries has led to streamlined synthesis of multiple structurally-complex, post-translationally modified proteins. In this review, we aim to summarize the latest chemical synthesis of thiolated and selenylated amino-acid building blocks and exemplify their important roles in conquering challenging protein targets with distinct PTM patterns.

Quinoline-Based Photolabile Protection Strategy Facilitates Efficient Protein Assembly

Native chemical ligation (NCL) provides a powerful solution to assemble proteins with precise chemical features, which enables a detailed investigation of the protein structure-function relationship. As an extension to NCL, the discovery of desulfurization and expressed protein ligation (EPL) techniques has greatly expanded the efficient access to large or challenging protein sequences via chemical ligations. Despite its superior reliability, the NCL-desulfurization protocol requires orthogonal protection strategies to allow selective desulfurization in the presence of native Cys, which is crucial to its synthetic application. In contrast to traditional thiol protecting groups, photolabile protecting groups (PPGs), which are removed upon irradiation, simplify protein assembly and therefore provide minimal perturbation to the peptide scaffold. However, current PPG strategies are mainly limited to nitro-benzyl derivatives, which are incompatible with NCL-desulfurization. Herein, we present for the first time that quinoline-based PPG for cysteine can facilitate various ligation strategies, including iterative NCL and EPL-desulfurization methods. 7-(Piperazin-1-yl)-2-(methyl)quinolinyl (PPZQ) caging of multiple cysteine residues within the protein sequence can be readily introduced via late-stage modification, while the traceless removal of PPZQ is highly efficient via photolysis in an aqueous buffer. In addition, the PPZQ group is compatible with radical desulfurization. The efficiency of this strategy has been highlighted by the synthesis of γ-synuclein and phosphorylated cystatin-S via one-pot iterative ligation and EPL-desulfurization methods. Besides, successful sextuple protection and deprotection of the expressed Interleukin-34 fragment demonstrate the great potential of this strategy in protein caging/uncaging investigations.

Total Chemical Synthesis of Correctly Folded Disulfide-Rich Proteins Using a Removable O-Linked β-N-Acetylglucosamine Strategy

Disulfide-rich proteins are useful as drugs or tool molecules in biomedical studies, but their synthesis is complicated by the difficulties associated with their folding. Here, we describe a removable glycosylation modification (RGM) strategy that expedites the chemical synthesis of correctly folded proteins with multiple or even interchain disulfide bonds. Our strategy comprises the introduction of simple O-linked β-N-acetylglucosamine (O-GlcNAc) groups at the Ser/Thr sites that effectively improve the folding of disulfide-rich proteins by stabilization of their folding intermediates. After folding, the O-GlcNAc groups can be efficiently removed using O-GlcNAcase (OGA) to afford the correctly folded proteins. Using this strategy, we completed the synthesis of correctly folded hepcidin, an iron-regulating hormone bearing four pairs of disulfide-bonds, and the first total synthesis of correctly folded interleukin-5 (IL-5), a 26 kDa homodimer cytokine responsible for eosinophil growth and differentiation.

Recent advances in synthetic glycoengineering for biological applications

Carbohydrates are involved in many important biological events such as protein maturation and trafficking, pathogen invasion, immune response, cell-cell communications, and so on. Synthetic and chemoenzymatic approaches for glycoengineering have emerged and been applied in perturbing and modulating the biological processes at the protein or cellular level. In this review, we summarize the recent advances in glycoengineering, including new strategies in chemoenzymatic synthesis of glycans, glycopeptides, glycoproteins, and other glycoconjugates. And, the progresses of cell surface glyco-editing methods for gain of functions are also discussed.

Sulfated Glycoprotein Synthesis

Chemical protein synthesis has achieved tremendous progress in the past decades. With the development of chemical ligation as powerful tools, the scope of synthetic protein is greatly expanded. Proteoglycans are a class of sulfated glycoproteins widely distributed on the cell surface and in the extracellular matrix, which are extensively engaged in cellular communication events. Consisting of protein backbone and glycosaminoglycan(s) side chain, proteoglycans are highly complex and heterogeneous in nature. Chemical synthesis provides facile and reliable approach to these molecules, with defined glycan structure and sulfation pattern. One remaining problem is that the acid-labile sulfates could hardly survive during the typical solid phase peptide synthesis (SPPS) process. In this chapter, strategic design of a "glycopeptide cassette" for the preparation of sulfated glycoprotein is described. In particular, we provide protocols for the chemical synthesis of ectodomain fragment (23-120) of sulfated glycoprotein syndecan-1.

Nanobody as solubilization chaperone for the expression and purification of inclusion-body prone proteins

Here we report a new protocol for enhancing the soluble expression of inclusion body (IB)-prone proteins in E. coli using nanobody (Nb) as a molecular-specific chaperone. The specific intracellular binding...

Chemical Synthesis of a Full-Length G-Protein-Coupled Receptor β2-Adrenergic Receptor with Defined Modification Patterns at the C-Terminus

The β₂-adrenergic receptor (β₂AR) is a G-protein-coupled receptor (GPCR) that responds to the hormone adrenaline and is an important drug target in the context of respiratory diseases, including asthma. β₂AR function can be regulated by post-translational modifications such as phosphorylation and ubiquitination at the C-terminus, but access to the full-length β₂AR with well-defined and homogeneous modification patterns critical for biochemical and biophysical studies remains challenging. Here, we report a practical synthesis of differentially modified, full-length β₂AR based on a combined native chemical ligation (NCL) and sortase ligation strategy. An array of homogeneous samples of full-length β₂ARs with distinct modification patterns, including a full-length β₂AR bearing both monoubiquitination and octaphosphorylation modifications, were successfully prepared for the first time. Using these homogeneously modified full-length β₂AR receptors, we found that different phosphorylation patterns mediate different interactions with β-arrestin1 as reflected in different agonist binding affinities. Our experiments also indicated that ubiquitination can further modulate interactions between β₂AR and β-arrestin1. Access to full-length β₂AR with well-defined and homogeneous modification patterns at the C-terminus opens a door to further in-depth mechanistic studies into the structure and dynamics of β₂AR complexes with downstream transducer proteins, including G proteins, arrestins, and GPCR kinases.

Glycoprotein Semisynthesis by Chemical Insertion of Glycosyl Asparagine Using a Bifunctional Thioacid-Mediated Strategy

Glycosylation is a major modification of secreted and cell surface proteins, and the resultant glycans show considerable heterogeneity in their structures. To understand the biological processes arising from each glycoform, the preparation of homogeneous glycoproteins is essential for extensive biological experiments. To establish a more robust and rapid synthetic route for the synthesis of homogeneous glycoproteins, we studied several key reactions based on amino thioacids. We found that diacyl disulfide coupling (DDC) formed with glycosyl asparagine thioacid and peptide thioacid yielded glycopeptides. This efficient coupling reaction enabled us to develop a new glycoprotein synthesis method, such as the bifunctional thioacid-mediated strategy, which can couple two peptides with the N- and C-termini of glycosyl asparagine thioacid. Previous glycoprotein synthesis methods required valuable glycosyl asparagine in the early stage and subsequent multiple glycoprotein synthesis routes, whereas the developed concept can generate glycoproteins within a few steps from peptide and glycosyl asparagine thioacid. Herein, we report the characterization of the DDC of amino thioacids and the efficient ability of glycosyl asparagine thioacid to be used for robust glycoprotein semisynthesis.