Role of glycosylation in nucleating protein folding and stability

Impact of glycosylation on viral vaccines

Glycosylation is the most prominent modification important for vaccines and its specific pattern depends on several factors that need to be considered when developing a new biopharmaceutical. Tailor-made glycosylation can be exploited to develop more effective and safer vaccines; for this reason, a deep understanding of both glycoengineering strategies and glycans structures and functions is required. In this review we discuss the recent advances concerning glycoprotein expression systems and the explanation of glycans immunomodulation mechanisms. Furthermore, we highlight how glycans tune the immunological properties among different vaccines platforms (whole virus, recombinant protein, nucleic acid), also comparing commercially available formulations and describing the state-of-the-art analytical technologies for glycosylation analysis. The whole review stresses the aspect of glycoprotein glycans as a potential tool to overcome nowadays medical needs in vaccine field.

Glycosylation: mechanisms, biological functions and clinical implications

Protein post-translational modification (PTM) is a covalent process that occurs in proteins during or after translation through the addition or removal of one or more functional groups, and has a profound effect on protein function. Glycosylation is one of the most common PTMs, in which polysaccharides are transferred to specific amino acid residues in proteins by glycosyltransferases. A growing body of evidence suggests that glycosylation is essential for the unfolding of various functional activities in organisms, such as playing a key role in the regulation of protein function, cell adhesion and immune escape. Aberrant glycosylation is also closely associated with the development of various diseases. Abnormal glycosylation patterns are closely linked to the emergence of various health conditions, including cancer, inflammation, autoimmune disorders, and several other diseases. However, the underlying composition and structure of the glycosylated residues have not been determined. It is imperative to fully understand the internal structure and differential expression of glycosylation, and to incorporate advanced detection technologies to keep the knowledge advancing. Investigations on the clinical applications of glycosylation focused on sensitive and promising biomarkers, development of more effective small molecule targeted drugs and emerging vaccines. These studies provide a new area for novel therapeutic strategies based on glycosylation.

Muscle-specific lack of Gfpt1 triggers ER stress to alleviate misfolded protein accumulation

Pathogenic variants in GFPT1, encoding a key enzyme to synthesize UDP-N-acetylglucosamine (UDP-GlcNAc), cause congenital myasthenic syndrome (CMS). We made a knock-in (KI) mouse model carrying a frameshift variant in Gfpt1 exon 9, simulating that found in a patient with CMS. As Gfpt1 exon 9 is exclusively expressed in striated muscles, Gfpt1-KI mice were deficient for Gfpt1 only in skeletal muscles. In Gfpt1-KI mice, (1) UDP-HexNAc, CMP-NeuAc and protein O-GlcNAcylation were reduced in skeletal muscles; (2) aged Gfpt1-KI mice showed poor exercise performance and abnormal neuromuscular junction structures; and (3) markers of the unfolded protein response (UPR) were elevated in skeletal muscles. Denervation-mediated enhancement of endoplasmic reticulum (ER) stress in Gfpt1-KI mice facilitated protein folding, ubiquitin-proteasome degradation and apoptosis, whereas autophagy was not induced and protein aggregates were markedly increased. Lack of autophagy was accounted for by enhanced degradation of FoxO1 by increased Xbp1-s/u proteins. Similarly, in Gfpt1-silenced C2C12 myotubes, ER stress exacerbated protein aggregates and activated apoptosis, but autophagy was attenuated. In both skeletal muscles in Gfpt1-KI mice and Gfpt1-silenced C2C12 myotubes, maladaptive UPR failed to eliminate protein aggregates and provoked apoptosis.

Differential glycosylation in mutant vitamin D-binding protein decimates the binding stability of vitamin D

Vitamin D (VD) is produced by the skin upon exposure to sunlight or is obtained from dietary sources. Several risk factors are associated with VD deficiency including mutations and post-translational modifications in its transport protein known as vitamin D binding protein (VDBP) or GC-globulin. The two common single nucleotide polymorphisms rs7041 and rs4588 create three major isoforms of VDBP, including GC-1F also called wild type, GC1S, and GC-2. The 3D models for both GC-1F and GC-2 were constructed in their glycosylated states to decipher the effect of these mutations on the overall conformational changes and VD-binding affinity. The binding affinities were estimated using the Molecular Mechanics Poison-Boltzmann surface area (MM-PBSA) method and conformational changes were investigated after free energy landscapes estimations. Total free energies suggest that GC-1F exhibits stronger affinity (ΔE = -116.09 kJ/mol) than GC-2 (ΔE = -95 kJ/mol) variant with VD. The GC-1F isoforms had more streamlined motion compared to GC-2 isoforms, predicting a trade-off between cross-talk residues that significantly impacts protein structural stability. The data suggest that glycation at Thr418 plays a vital role in the overall VDBP-VD affinity by stabilizing the N-T loop that holds the domain I (VD-pocket) and domain III intact. The loss of glycation in GC-2 has a pivotal role in the inter-domain conformational stability of VDBP, which may ultimately affect VD transportation and maturation. These findings describe a novel mechanism in how mutations distant from the VD-active site change the overall conformational of the VDBP and abrogate the VDBP-VD interaction.Communicated by Ramaswamy H. Sarma.

A novel prolixicin identified in common bed bugs with activity against both bacteria and parasites

The hematophagous common bed bug, Cimex lectularius, is not known to transmit human pathogens outside laboratory settings, having evolved various immune defense mechanisms including the expression of antimicrobial peptides (AMPs). We unveil three novel prolixicin AMPs in bed bugs, exhibiting strong homology to the prolixicin of kissing bugs, Rhodnius prolixus, and to diptericin/attacin AMPs. We demonstrate for the first time sex-specific and immune mode-specific upregulation of these prolixicins in immune organs, the midgut and rest of body, following injection and ingestion of Gr+ (Bacillus subtilis) and Gr- (Escherichia coli) bacteria. Synthetic CL-prolixicin2 significantly inhibited growth of E. coli strains and killed or impeded Trypanosoma cruzi, the Chagas disease agent. Our findings suggest that prolixicins are regulated by both IMD and Toll immune pathways, supporting cross-talk and blurred functional differentiation between major immune pathways. The efficacy of CL-prolixicin2 against T. cruzi underscores the potential of AMPs in Chagas disease management.

ZNT5-6 and ZNT7 play an integral role in protein N-glycosylation by supplying Zn2+ to Golgi α-mannosidase II

The stepwise addition of monosaccharides to N-glycans attached to client proteins to generate a repertoire of mature proteins involves a concerted action of many glycosidases and glycosyltransferases. Here, we report that Golgi α-mannosidase II (GMII), a pivotal enzyme catalyzing the first step in the conversion of hybrid- to complex-type N-glycans, is activated by Zn2+ supplied by the early secretory compartment-resident ZNT5-ZNT6 heterodimers (ZNT5-6) and ZNT7 homodimers (ZNT7). Loss of ZNT5-6 and ZNT7 function results in marked accumulation of hybrid-type and complex/hybrid glycans with concomitant reduction of complex- and high-mannose-type glycans. In cells lacking the ZNT5-6 and ZNT7 functions, the GMII activity is substantially decreased. In contrast, the activity of its homolog, lysosomal mannosidase (LAMAN), is not decreased. Moreover, we show that the growth of pancreatic cancer MIA PaCa-2 cells lacking ZNT5-6 and ZNT7 is significantly decreased in a nude mouse xenograft model. Our results indicate the integral roles of ZNT5-6 and ZNT7 in N-glycosylation and highlight their potential as novel target proteins for cancer therapy.

Evaluating the Role of Neddylation Modifications in Kidney Renal Clear Cell Carcinoma: An Integrated Approach Using Bioinformatics, MLN4924 Dosing Experiments, and RNA Sequencing

BACKGROUND

Neddylation, a post-translational modification process, plays a crucial role in various human neoplasms. However, its connection with kidney renal clear cell carcinoma (KIRC) remains under-researched.

METHODS

We validated the Gene Set Cancer Analysis Lite (GSCALite) platform against The Cancer Genome Atlas (TCGA) database, analyzing 33 cancer types and their link with 17 neddylation-related genes. This included examining copy number variations (CNVs), single nucleotide variations (SNVs), mRNA expression, cellular pathway involvement, and methylation. Using Gene Set Variation Analysis (GSVA), we categorized these genes into three clusters and examined their impact on KIRC patient prognosis, drug responses, immune infiltration, and oncogenic pathways. Afterward, our objective is to identify genes that exhibit overexpression in KIRC and are associated with an adverse prognosis. After pinpointing the specific target gene, we used the specific inhibitor MLN4924 to inhibit the neddylation pathway to conduct RNA sequencing and related in vitro experiments to verify and study the specificity and potential mechanisms related to the target. This approach is geared towards enhancing our understanding of the prognostic importance of neddylation modification in KIRC.

RESULTS

We identified significant CNV, SNV, and methylation events in neddylation-related genes across various cancers, with notably higher expression levels observed in KIRC. Cluster analysis revealed a potential trade-off in the interactions among neddylation-related genes, where both high and low levels of gene expression are linked to adverse prognoses. This association is particularly pronounced concerning lymph node involvement, T stage classification, and Fustat score. Simultaneously, our research discovered that PSMB10 exhibits overexpression in KIRC when compared to normal tissues, negatively impacting patient prognosis. Through RNA sequencing and in vitro assays, we confirmed that the inhibition of neddylation modification could play a role in the regulation of various signaling pathways, thereby influencing the prognosis of KIRC. Moreover, our results underscore PSMB10 as a viable target for therapeutic intervention in KIRC, opening up novel pathways for the development of targeted treatment strategies.

CONCLUSION

This study underscores the regulatory function and potential mechanism of neddylation modification on the phenotype of KIRC, identifying PSMB10 as a key regulatory target with a significant role in influencing the prognosis of KIRC.

Role of N-linked glycosylation in porcine reproductive and respiratory syndrome virus (PRRSV) infection

Porcine reproductive and respiratory syndrome (PRRSV) is an enveloped single-stranded positive-sense RNA virus and one of the main pathogens that causes the most significant economical losses in the swine-producing countries. PRRSV is currently divided into two distinct species, PRRSV-1 and PRRSV-2. The PRRSV virion envelope is composed of four glycosylated membrane proteins and three non-glycosylated envelope proteins. Previous work has suggested that PRRSV-linked glycans are critical structural components for virus assembly. In addition, it has been proposed that PRRSV glycans are implicated in the interaction with host cells and critical for virus infection. In contrast, recent findings showed that removal of N-glycans from PRRSV does not influence virus infection of permissive cells. Thus, there are not sufficient evidences to indicate compellingly that N-glycans present in the PRRSV envelope play a direct function in viral infection. To gain insights into the role of N-glycosylation in PRRSV infection, we analysed the specific contribution of the envelope protein-linked N-glycans to infection of permissive cells. For this purpose, we used a novel strategy to modify envelope protein-linked N-glycans that consists of production of monoglycosylated PRRSV and viral glycoproteins with different glycan states. Our results showed that removal or alteration of N-glycans from PRRSV affected virus infection. Specifically, we found that complex N-glycans are required for an efficient infection in cell cultures. Furthermore, we found that presence of high mannose type glycans on PRRSV surface is the minimal requirement for a productive viral infection. Our findings also show that PRRSV-1 and PRRSV-2 have different requirements of N-glycan structure for an optimal infection. In addition, we demonstrated that removal of N-glycans from PRRSV does not affect viral attachment, suggesting that these carbohydrates played a major role in regulating viral entry. In agreement with these findings, by performing immunoprecipitation assays and colocalization experiments, we found that N-glycans present in the viral envelope glycoproteins are not required to bind to the essential viral receptor CD163. Finally, we found that the presence of N-glycans in CD163 is not required for PRRSV infection.

Pharmacological suppression of HHLA2 glycosylation restores anti-tumor immunity in colorectal cancer

Immunotherapy aimed at inhibiting the negative co-stimulatory molecule programmed cell death-ligand 1 (PD-L1) has limited effectiveness, with clinical response rates remaining below 10%-15%. Therefore, new immune checkpoints need to be explored. Our study focused on human endogenous retrovirus H long terminal repeat-associating protein 2 (HHLA2), a highly glycosylated member of the B7 family that is widely expressed in colorectal cancer. HHLA2 expression negatively correlates with the prognosis of colorectal cancer. Glycosylation of HHLA2, which is regulated by the glycosyltransferase STT3 oligosaccharyltransferase complex catalytic subunit A (STT3A), is crucial for protein stability and expression in cell membranes. Additionally, the binding of HHLA2 to the receptors killer cell immunoglobulin-like receptor, three immunoglobulin domains and long cytoplasmic tail 3 (KIR3DL3) and transmembrane and immunoglobulin (Ig) domain containing 2 (TMIGD2) is dependent on N-glycosylation. Moreover, N-glycosylation of HHLA2 promotes immune evasion in colorectal cancer by suppressing the immune response of NK cells. Notably, the STT3A inhibitor NGI-1 enhances the anti-tumor immune response of NK cells. Our findings provide new insights and a molecular basis for targeting HHLA2 in immunotherapy for colorectal cancer.

Revisiting the immunopathology of congenital disorders of glycosylation: an updated review

Glycosylation is a critical post-translational modification that plays a pivotal role in several biological processes, such as the immune response. Alterations in glycosylation can modulate the course of various pathologies, such as the case of congenital disorders of glycosylation (CDG), a group of more than 160 rare and complex genetic diseases. Although the link between glycosylation and immune dysfunction has already been recognized, the immune involvement in most CDG remains largely unexplored and poorly understood. In this study, we provide an update on the immune dysfunction and clinical manifestations of the 12 CDG with major immune involvement, organized into 6 categories of inborn errors of immunity according to the International Union of Immunological Societies (IUIS). The immune involvement in phosphomannomutase 2 (PMM2)-CDG - the most frequent CDG - was comprehensively reviewed, highlighting a higher prevalence of immune issues during infancy and childhood and in R141H-bearing genotypes. Finally, using PMM2-CDG as a model, we point to links between abnormal glycosylation patterns in host cells and possibly favored interactions with microorganisms that may explain the higher susceptibility to infection. Further characterizing immunopathology and unusual host-pathogen adhesion in CDG can not only improve immunological standards of care but also pave the way for innovative preventive measures and targeted glycan-based therapies that may improve quality of life for people living with CDG.

L-Glycosidase-Cleavable Natural Glycans Facilitate the Chemical Synthesis of Correctly Folded Disulfide-Bonded D-Proteins

D-peptide ligands can be screened for therapeutic potency and enzymatic stability using synthetic mirror-image proteins (D-proteins), but efficient acquisition of these D-proteins can be hampered by the need to accomplish their in vitro folding, which often requires the formation of correctly linked disulfide bonds. Here, we report the finding that temporary installation of natural O-linked-β-N-acetyl-D-glucosamine (O-GlcNAc) groups onto selected D-serine or D-threonine residues of the synthetic disulfide-bonded D-proteins can facilitate their folding in vitro, and that the natural glycosyl groups can be completely removed from the folded D-proteins to afford the desired chirally inverted D-protein targets using naturally occurring O-GlcNAcase. This approach enabled the efficient chemical syntheses of several important but difficult-to-fold D-proteins incorporating disulfide bonds including the mirror-image tumor necrosis factor alpha (D-TNFα) homotrimer and the mirror-image receptor-binding domain of the Omicron spike protein (D-RBD). Our work establishes the use of O-GlcNAc to facilitate D-protein synthesis and folding and proves that D-proteins bearing O-GlcNAc can be good substrates for naturally occurring O-GlcNAcase.

Targeted Analysis of Permethylated N-Glycans Using MRM/PRM Approaches

Targeted mass spectrometric analysis is widely employed across various omics fields as a validation strategy due to its high sensitivity and accuracy. The approach has been successfully employed for the structural analysis of proteins, glycans, lipids, and metabolites. Multiple reaction monitoring (MRM) and parallel reaction monitoring (PRM) have been the methods of choice for targeted structural studies of biomolecules. These target analyses simplify the analytical workflow, reduce background interference, and increase selectivity/specificity, allowing for a reliable quantification of permethylated N-glycans in complex biological matrices.

Lipidization as a tool toward peptide therapeutics

Peptides, as potential therapeutics continue to gain importance in the search for active substances for the treatment of numerous human diseases, some of which are, to this day, incurable. As potential therapeutic drugs, peptides have many favorable chemical and pharmacological properties, starting with their great diversity, through their high affinity for binding to all sort of natural receptors, and ending with the various pathways of their breakdown, which produces nothing but amino acids that are nontoxic to the body. Despite these and other advantages, however, they also have their pitfalls. One of these disadvantages is the very low stability of natural peptides. They have a short half-life and tend to be cleared from the organism very quickly. Their instability in the gastrointestinal tract, makes it impossible to administer peptidic drugs orally. To achieve the best pharmacologic effect, it is desirable to look for ways of modifying peptides that enable the use of these substances as pharmaceuticals. There are many ways to modify peptides. Herein we summarize the approaches that are currently in use, including lipidization, PEGylation, glycosylation and others, focusing on lipidization. We describe how individual types of lipidization are achieved and describe their advantages and drawbacks. Peptide modifications are performed with the goal of reaching a longer half-life, reducing immunogenicity and improving bioavailability. In the case of neuropeptides, lipidization aids their activity in the central nervous system after the peripheral administration. At the end of our review, we summarize all lipidized peptide-based drugs that are currently on the market.

Glycosylation and Crowded Membrane Effects on Influenza Neuraminidase Stability and Dynamics

All protein simulations are conducted with varying degrees of simplification, oftentimes with unknown ramifications about how these simplifications affect the interpretability of the results. In this work, we investigated how protein glycosylation and lateral crowding effects modulate an array of properties characterizing the stability and dynamics of influenza neuraminidase. We constructed three systems: (1) glycosylated neuraminidase in a whole virion (i.e., crowded membrane) environment, (2) glycosylated neuraminidase in its own lipid bilayer, and (3) unglycosylated neuraminidase in its own lipid bilayer. We saw that glycans tend to stabilize the protein structure and reduce its conformational flexibility while restricting the solvent movement. Conversely, a crowded membrane environment encouraged exploration of the free energy landscape and a large-scale conformational change, while making the protein structure more compact. Understanding these effects informs what factors one must consider in attempting to recapture the desired level of physical accuracy.

Disruption of sugar nucleotide clearance is a therapeutic vulnerability of cancer cells

Identifying metabolic steps that are specifically required for the survival of cancer cells but are dispensable in normal cells remains a challenge1. Here we report a therapeutic vulnerability in a sugar nucleotide biosynthetic pathway that can be exploited in cancer cells with only a limited impact on normal cells. A systematic examination of conditionally essential metabolic enzymes revealed that UXS1, a Golgi enzyme that converts one sugar nucleotide (UDP-glucuronic acid, UDPGA) to another (UDP-xylose), is essential only in cells that express high levels of the enzyme immediately upstream of it, UGDH. This conditional relationship exists because UXS1 is required to prevent excess accumulation of UDPGA, which is produced by UGDH. UXS1 not only clears away UDPGA but also limits its production through negative feedback on UGDH. Excess UDPGA disrupts Golgi morphology and function, which impedes the trafficking of surface receptors such as EGFR to the plasma membrane and diminishes the signalling capacity of cells. UGDH expression is elevated in several cancers, including lung adenocarcinoma, and is further enhanced during chemoresistant selection. As a result, these cancer cells are selectively dependent on UXS1 for UDPGA detoxification, revealing a potential weakness in tumours with high levels of UGDH.

Niclosamide improves cancer immunotherapy by modulating RNA-binding protein HuR-mediated PD-L1 signaling

BACKGROUND

Immune checkpoint blockade (ICB) represents a revolutionary advance in cancer treatment but remains limited success in triple-negative breast cancer (TNBC). Here we aim to explore the mechanism of RNA-binding protein (RBP) HuR in cancer immune evasion by post-transcriptionally regulating PD-L1 and evaluate the potential of HuR inhibition to improve immune response.

METHODS

The binding between HuR and PD-L1 mRNA was determined by ribonucleoprotein immunoprecipitation and RNA pull-down assays. The HuR knockout clones were established by CRISPR/Cas9 technology. The protein levels were assessed by Western blot, immunohistochemistry, and immunocytochemistry. The function and molecular mechanism of HuR-PD-L1 were determined by in vitro T cell activation and killing assay and in vivo efficacy assay.

RESULTS

We found that HuR directly bound to and stabilized PD-L1 mRNA. Knocking out HuR reduced PD-L1 levels and promoted T cell activation. We discovered that niclosamide reduced PD-L1 by inhibiting HuR cytoplasmic translocation, and diminished glycosylation of PD-L1. Niclosamide enhanced T cell-mediated killing of cancer cells and significantly improved the efficacy of anti-PD-1 immunotherapy in two syngeneic animal tumor models.

CONCLUSION

We identified HuR as a novel posttranscriptional regulator of PD-L1, which plays an important role in tumor immune evasion. Niclosamide might be a promising repurposed drug to improve the patient response to immunotherapy by targeting HuR-PD-L1 axis. Our study demonstrates a novel strategy for targeting HuR/PD-L1 and provides the first proof-of-principle for repurposing niclosamide as a HuR inhibitor to overcome cancer immune evasion and improve response to ICB immunotherapy.

Glycosylation and Crowded Membrane Effects on Influenza Neuraminidase Stability and Dynamics

All protein simulations are conducted with varying degrees of simplifications, oftentimes with unknown ramifications on how these simplifications affect the interpretability of the results. In this work we investigated how protein glycosylation and lateral crowding effects modulate an array of properties characterizing the stability and dynamics of influenza neuraminidase. We constructed three systems: 1) Glycosylated neuraminidase in a whole virion (i.e. crowded membrane) environment 2) Glycosylated neuraminidase in its own lipid bilayer 3) Unglycosylated neuraminidase in its own lipid bilayer. We saw that glycans tend to stabilize the protein structure and reduce its conformational flexibility while restricting solvent movement. Conversely, a crowded membrane environment encouraged exploration of the free energy landscape and a large scale conformational change while making the protein structure more compact. Understanding these effects informs what factors one must consider while attempting to recapture the desired level of physical accuracy.

Biomanufacturing of γ-linolenic acid-enriched galactosyldiacylglycerols: Challenges in microalgae and potential in oleaginous yeasts

γ-Linolenic acid-enriched galactosyldiacylglycerols (GDGs-GLA), as the natural form of γ-linolenic acid in microalgae, have a range of functional activities, including anti-inflammatory, antioxidant, and anti-allergic properties. The low abundance of microalgae and the structural stereoselectivity complexity impede microalgae extraction or chemical synthesis, resulting in a lack of supply of GDGs-GLA with a growing demand. At present, there is a growing interest in engineering oleaginous yeasts for mass production of GDGs-GLA based on their ability to utilize a variety of hydrophobic substrates and a high metabolic flux toward fatty acid and lipid (triacylglycerol, TAG) production. Here, we first introduce the GDGs-GLA biosynthetic pathway in microalgae and challenges in the engineering of the native host. Subsequently, we describe in detail the applications of oleaginous yeasts with Yarrowia lipolytica as the representative for GDGs-GLA biosynthesis, including the development of synthetic biology parts, gene editing tools, and metabolic engineering of lipid biosynthesis. Finally, we discuss the development trend of GDGs-GLA biosynthesis in Y. lipolytica.

Linking aberrant glycosylation of plasma glycoproteins with progression of myelodysplastic syndromes: a study based on plasmonic biosensor and lectin array

Aberrant glycosylation of glycoproteins has been linked with various pathologies. Therefore, understanding the relationship between aberrant glycosylation patterns and the onset and progression of the disease is an important research goal that may provide insights into cancer diagnosis and new therapy development. In this study, we use a surface plasmon resonance imaging biosensor and a lectin array to investigate aberrant glycosylation patterns associated with oncohematological disease-myelodysplastic syndromes (MDS). In particular, we detected the interaction between the lectins and glycoproteins present in the blood plasma of patients (three MDS subgroups with different risks of progression to acute myeloid leukemia (AML) and AML patients) and healthy controls. The interaction with lectins from Aleuria aurantia (AAL) and Erythrina cristagalli was more pronounced for plasma samples of the MDS and AML patients, and there was a significant difference between the sensor response to the interaction of AAL with blood plasma from low and medium-risk MDS patients and healthy controls. Our data also suggest that progression from MDS to AML is accompanied by sialylation of glycoproteins and increased levels of truncated O-glycans and that the number of lectins that allow discriminating different stages of disease increases as the disease progresses.

Regulation of post-translational modification of PD-L1 and advances in tumor immunotherapy

The immune checkpoint molecules programmed cell death receptor 1 (PD-1) and programmed death ligand 1 (PD-L1) are one of the most promising targets for tumor immunotherapy. PD-L1 is overexpressed on the surface of tumor cells and inhibits T cell activation upon binding to PD⁃1 on the surface of T cells, resulting in tumor immune escape. The therapeutic strategy of targeting PD-1/PD-L1 involves blocking this binding and restoring the tumor-killing effect of immune cells. However, in clinical settings, a relatively low proportion of cancer patients have responded well to PD-1/PD-L1 blockade, and clinical outcomes have reached a bottleneck and no substantial progress has been made. In recent years, PD-L1 post-translation modifications (PTMs) have gradually become a hot topic in the field of PD-L1 research, which will provide new insights to improve the efficacy of current anti-PD-1/PD-L1 therapies. Here, we summarized and discussed multiple PTMs of PD-L1, including glycosylation, ubiquitination, phosphorylation, acetylation and palmitoylation, with a major emphasis on mechanism-based therapeutic strategies (including relevant enzymes and targets that are already in clinical use and that may become drugs in the future). We also summarized the latest research progress of PTMs of PD-L1/PD-1 in regulating immunotherapy. The review provided novel strategies and directions for tumor immunotherapy research based on the PTMs of PD-L1/PD-1.

Altered profile of glycosylated proteins in serum samples obtained from patients with Hashimoto's thyroiditis following depletion of highly abundant proteins

Objectives

Hashimoto's thyroiditis (HT) is one of the most common autoimmune disorders; however, its underlying pathological mechanisms remain unclear. Although aberrant glycosylation has been implicated in the N-glycome of immunoglobulin G (IgG), changes in serum proteins have not been comprehensively characterized. This study aimed to investigate glycosylation profiles in serum samples depleted of highly abundant proteins from patients with HT and propose the potential functions of glycoproteins for further studies on the pathological mechanisms of HT.

Methods

A lectin microarray containing 70 lectins was used to detect and analyze glycosylation of serum proteins using serum samples (N=27 HT; N=26 healthy control [HC]) depleted of abundant proteins. Significant differences in glycosylation status between HT patients and the HC group were verified using lectin blot analysis. A lectin-based pull-down assay combined with mass spectrometry was used to investigate potential glycoproteins combined with differentially present lectins, and an enzyme-linked immunosorbent assay (ELISA) was used to identify the expression of targeted glycoproteins in 131 patients with papillary thyroid carcinoma (PTC), 131 patients with benign thyroid nodules (BTN) patients, 130 patients with HT, and 128 HCs.

Results

Compared with the HC group, the majority of the lectin binding signals in HT group were weakened, while the Vicia villosa agglutinin (VVA) binding signal was increased. The difference in VVA binding signals verified by lectin blotting was consistent with the results of the lectin microarray. A total of 113 potential VVA-binding glycoproteins were identified by mass spectrometry and classified by gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) analyses. Using ELISA, we confirmed that lactoferrin (LTF) and mannan-binding lectin-associated serine protease 1 (MASP-1) levels were elevated in the serum of patients with HT and PTC.

Conclusion

Following depletion of abundant proteins, remaining serum proteins in HT patients exhibited lower glycosylation levels than those observed in HCs. An increased level of potential VVA-binding glycoproteins may play an important role in HT development. LTF and MASP-1 expression was significantly higher in the serum of HT and PTC patients, providing novel insight into HT and PTC.

Osteopontin as a Biomarker in Chronic Kidney Disease

Osteopontin (OPN) is a ubiquitously expressed protein with a wide range of physiological functions, including roles in bone mineralization, immune regulation, and wound healing. OPN has been implicated in the pathogenesis of several forms of chronic kidney disease (CKD) where it promotes inflammation and fibrosis and regulates calcium and phosphate metabolism. OPN expression is increased in the kidneys, blood, and urine of patients with CKD, particularly in those with diabetic kidney disease and glomerulonephritis. The full-length OPN protein is cleaved by various proteases, including thrombin, matrix metalloproteinase (MMP)-3, MMP-7, cathepsin-D, and plasmin, producing N-terminal OPN (ntOPN), which may have more detrimental effects in CKD. Studies suggest that OPN may serve as a biomarker in CKD, and while more research is needed to fully evaluate and validate OPN and ntOPN as CKD biomarkers, the available evidence suggests that they are promising candidates for further investigation. Targeting OPN may be a potential treatment strategy. Several studies show that inhibition of OPN expression or activity can attenuate kidney injury and improve kidney function. In addition to its effects on kidney function, OPN has been linked to cardiovascular disease, which is a major cause of morbidity and mortality in patients with CKD.

Recombinant protein expression: Challenges in production and folding related matters

Protein folding is a biophysical process by which proteins reach a specific three-dimensional structure. The amino acid sequence of a polypeptide chain contains all the information needed to determine the final three-dimensional structure of a protein. When producing a recombinant protein, several problems can occur, including proteolysis, incorrect folding, formation of inclusion bodies, or protein aggregation, whereby the protein loses its natural structure. To overcome such limitations, several strategies have been developed to address each specific issue. Identification of proper protein refolding conditions can be challenging, and to tackle this high throughput screening for different recombinant protein folding conditions can prove a sound solution. Different approaches have emerged to tackle refolding issues. One particular approach to address folding issues involves molecular chaperones, highly conserved proteins that contribute to proper folding by shielding folding proteins from other proteins that could hinder the process. Proper protein folding is one of the main prerequisites for post-translational modifications. Incorrect folding, if not dealt with, can lead to a buildup of protein misfoldings that damage cells and cause widespread abnormalities. Said post-translational modifications, widespread in eukaryotes, are critical for protein structure, function and biological activity. Incorrect post-translational protein modifications may lead to individual consequences or aggregation of therapeutic proteins. In this review article, we have tried to examine some key aspects of recombinant protein expression. Accordingly, the relevance of these proteins is highlighted, major problems related to the production of recombinant protein and to refolding issues are pinpointed and suggested solutions are presented. An overview of post-translational modification, their biological significance and methods of identification are also provided. Overall, the work is expected to illustrate challenges in recombinant protein expression.

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.

Inherited Thrombocytopenia Caused by Variants in Crucial Genes for Glycosylation

Protein glycosylation, including sialylation, involves complex and frequent post-translational modifications, which play a critical role in different biological processes. The conjugation of carbohydrate residues to specific molecules and receptors is critical for normal hematopoiesis, as it favors the proliferation and clearance of hematopoietic precursors. Through this mechanism, the circulating platelet count is controlled by the appropriate platelet production by megakaryocytes, and the kinetics of platelet clearance. Platelets have a half-life in blood ranging from 8 to 11 days, after which they lose the final sialic acid and are recognized by receptors in the liver and eliminated from the bloodstream. This favors the transduction of thrombopoietin, which induces megakaryopoiesis to produce new platelets. More than two hundred enzymes are responsible for proper glycosylation and sialylation. In recent years, novel disorders of glycosylation caused by molecular variants in multiple genes have been described. The phenotype of the patients with genetic alterations in GNE, SLC35A1, GALE and B4GALT is consistent with syndromic manifestations, severe inherited thrombocytopenia, and hemorrhagic complications.

Molecular Cloning and Characteristics of a Lectin from the Bivalve Glycymeris yessoensis

C-type lectins (CTLs) are a family of carbohydrate-binding proteins that mediate multiple biological events, including adhesion between cells, the turnover of serum glycoproteins, and innate immune system reactions to prospective invaders. Here, we describe the cDNA cloning of lectin from the bivalve Glycymeris yessoensis (GYL), which encodes 161 amino acids and the C-type carbohydrate recognition domain (CRD) with EPN and WND motifs. The deduced amino acid sequence showed similarity to other CTLs. GYL is a glycoprotein containing two N-glycosylation sites per subunit. N-glycans are made up of xylose, mannose, D-glucosamine, 3-O-methylated galactose, D-quinovoses, and 3-O-methylated 6-deoxy-D-glucose. The potential CRD tertiary structure of the GYL adopted CTL-typical long-form double-loop structure and included three disulfide bridges at the bases of the loops. Additionally, when confirming the GYL sequence, eight isoforms of this lectin were identified. This fact indicates the presence of a multigene family of GYL-like C-type lectins in the bivalve G. yessoensis. Using the glycan microarray approach, natural carbohydrate ligands were established, and the glycotope for GYL was reconstructed as "Galβ1-4GlcNAcβ obligatory containing an additional fragment", like a sulfate group or a methyl group of fucose or N-acetylgalactosamine residues.

Defining the altered glycoproteomic space of the early secretory pathway by class I mannosidase pharmacological inhibition

N-glycosylation is a key process for various biological functions like protein folding, maturation and sorting for the conventional secretory compartment, cell-cell communication and immune response. This is usually accomplished by a complex system of mannosidases in which those from class I have an outstanding role, commonly involved in the early protein sorting associated to the Endoplasmic Reticulum (ER) in the N-glycan dependent quality control (ERQC) and ER-associated degradation (ERAD). Although these are vital processes in maintaining cellular homeostasis, large-scale analysis studies for this pool of molecules, further denoted as proteins from the early secretory pathway (ESP), were limited addressed. Here, using a custom workflow employing a combination of glycomics and deglycoproteomics analyses, using lectin affinity and selective Endoglycosidase H (Endo H) digestion, we scrutinize the steady-state oligomannosidic glycoprotein load and delineate ESP fraction in melanoma cells. All of these were assessed by applying our workflow for glycosite relative quantification of both the peptide chain and carbohydrate structure in cells with inhibited activity of class I mannosidases after kifunensine treatment. We found that most of the ESP are transient clients involved in cell communication via extracellular matrix, particularly integrin-mediated communication which adopt Man9 N-glycans in kifunensine-treated cells. Moreover, our results reveal that core-fucosylation is decreased subsequent inhibition of class I mannosidases and this could be explained by a general lower protein level of FUT8, the enzyme responsible for fucosylation. By comparing our data with results obtained following downregulation of a key mannosidase in misfolded protein degradation, we mapped both novel and previously suggested endogenous substrate candidates like PCDH2, HLA-B, LAMB2 or members of the integrin family of proteins such as ITGA1 and ITGA4, thus validating the findings obtained using our workflow regarding accumulation and characterization of ESP transitory members following mannosidase class I inhibition. This workflow and the associated dataset not only allowed us to investigate the oligomannosidic glycoprotein fraction but also to delineate differences mediated at glycosite-level upon kifunensine treatment and outline the potential associated cellular responses.

Biomimetic Tweezers for N-Glycans: Selective Recognition of the Core GlcNAc2 Disaccharide of the Sialylglycopeptide SGP

In recent years, glycomics have shown how pervasive the role of carbohydrates in biological systems is and how chemical tools are essential to investigate glycan function and modulate carbohydrate-mediated processes. Biomimetic receptors for carbohydrates can carry out this task but, although significant affinities and selectivities toward simple saccharides have been achieved, targeting complex glycoconjugates remains a goal yet unattained. In this work we report the unprecedented recognition of a complex biantennary sialylglycopeptide (SGP) by a tweezers-shaped biomimetic receptor, which selectively binds to the core GlcNAc₂ disaccharide of the N-glycan with an affinity of 170 μM. Because of the simple structure and the remarkable binding ability, this biomimetic receptor can represent a versatile tool for glycoscience, opening the way to useful applications.

Identification of serum glycobiomarkers for Hepatocellular Carcinoma using lectin microarrays

Objective

Hepatocellular carcinoma (HCC) is the sixth most commonly occurring cancer and ranks third in mortality among all malignant tumors; as a result, HCC represents a major human health issue. Although aberrant glycosylation is clearly implicated in HCC, changes in serum immunoglobulin (Ig)G and IgM glycosylation have not been comprehensively characterized. In this study, we used lectin microarrays to evaluate differences in serum IgG and IgM glycosylation among patients with HCC, hepatitis B cirrhosis (HBC), or chronic hepatitis B (CHB), and healthy normal controls (NC) and aimed to establish a model to improve the diagnostic accuracy of HCC.

Methods

In total, 207 serum samples collected in 2019–2020 were used for lectin microarray analyses, including 97 cases of HCC, 50 cases of HBC, 30 cases of CHB, and 30 cases of NC. Samples were randomly divided into training and validation groups at a 2:1 ratio. Training group data were used to investigate the diagnostic value of the relative signal intensity for the lectin probe combined with alpha-fetoprotein (AFP). The efficacy of models for HCC diagnosis were analyzed by receiver operating characteristic (ROC) curves.

Results

In terms of IgG, a model combining three lectins and AFP had good diagnostic accuracy for HCC. The area under the ROC curve was 0.96 (P < 0.05), the sensitivity was 82.54%, and the specificity was 100%. In terms of IgM, a model including one lectin combined with AFP had an area under the curve of 0.90 (P < 0.05), sensitivity of 75.41%, and specificity of 100%.

Conclusion

Estimation of serum IgG and IgM glycosylation could act as complementary techniques to improve diagnosis and shed light on the occurrence and development of the HCC

Glycosylation of a key cubilin Asn residue results in reduced binding to albumin

Kidney disease often manifests with an increase in proteinuria, which can result from both glomerular and/or proximal tubule injury. The proximal tubules are the major site of protein and peptide endocytosis of the glomerular filtrate, and cubilin is the proximal tubule brush border membrane glycoprotein receptor that binds filtered albumin and initiates its processing in proximal tubules. Albumin also undergoes multiple modifications depending upon the physiologic state. We previously documented that carbamylated albumin had reduced cubilin binding, but the effects of cubilin modifications on binding albumin remain unclear. Here, we investigate the cubilin-albumin binding interaction to define the impact of cubilin glycosylation and map the key glycosylation sites while also targeting specific changes in a rat model of proteinuria. We identified a key Asn residue, N1285, that when glycosylated reduced albumin binding. In addition, we found a pH-induced conformation change may contribute to ligand release. To further define the albumin-cubilin binding site, we determined the solution structure of cubilin's albumin-binding domain, CUB7,8, using small-angle X-ray scattering and molecular modeling. We combined this information with mass spectrometry crosslinking experiments of CUB7,8 and albumin that provides a model of the key amino acids required for cubilin-albumin binding. Together, our data supports an important role for glycosylation in regulating the cubilin interaction with albumin, which is altered in proteinuria and provides new insight into the binding interface necessary for the cubilin-albumin interaction.

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

Enzyme immobilization has been developing since the 1960s and although many industrial biocatalytic processes use the technology to improve enzyme performance, still today we are far from full exploitation of the field. One clear reason is that many evaluate immobilization based on only a few experiments that are not always well-designed. In contrast to many other reviews on the subject, here we highlight the pitfalls of using incorrectly designed immobilization protocols and explain why in many cases sub-optimal results are obtained. We also describe solutions to overcome these challenges and come to the conclusion that recent developments in material science, bioprocess engineering and protein science continue to open new opportunities for the future. In this way, enzyme immobilization, far from being a mature discipline, remains as a subject of high interest and where intense research is still necessary to take full advantage of the possibilities.

Genome-wide screening identifies DNA methylation sites that regulate the blood proteome

Background: Identifying DNA methylation sites that regulate the blood proteome is important for biomedical purposes. Materials & methods: Here the authors performed a genome-wide search to find DNA methylation sites that impact proteins. Results: The authors identified 165 methylation sites associated with 138 proteins. The authors noted hotspot genomic regions that control the levels of several proteins. For example, methylation of the ABO locus impacted 37 proteins and contributed to cardiometabolic comorbidities, including the severity of SARS-CoV-2 infection. The authors made these findings publicly available as a Unix software that identifies methylation sites that cause disease and reveals the underlying proteins. The authors underlined the software application by showing that components of innate immunity contribute to systolic blood pressure. Conclusion: This study provides a catalog of DNA methylation sites that regulate the proteome, and the results are available as freeware for biological insight.

TNFα-induced metabolic reprogramming drives an intrinsic anti-viral state

Cytokines induce an anti-viral state, yet many of the functional determinants responsible for limiting viral infection are poorly understood. Here, we find that TNFα induces significant metabolic remodeling that is critical for its anti-viral activity. Our data demonstrate that TNFα activates glycolysis through the induction of hexokinase 2 (HK2), the isoform predominantly expressed in muscle. Further, we show that glycolysis is broadly important for TNFα-mediated anti-viral defense, as its inhibition attenuates TNFα’s ability to limit the replication of evolutionarily divergent viruses. TNFα was also found to modulate the metabolism of UDP-sugars, which are essential precursor substrates for glycosylation. Our data indicate that TNFα increases the concentration of UDP-glucose, as well as the glucose-derived labeling of UDP-glucose and UDP-N-acetyl-glucosamine in a glycolytically-dependent manner. Glycolysis was also necessary for the TNFα-mediated accumulation of several glycosylated anti-viral proteins. Consistent with the importance of glucose-driven glycosylation, glycosyl-transferase inhibition attenuated TNFα’s ability to promote the anti-viral cell state. Collectively, our data indicate that cytokine-mediated metabolic remodeling is an essential component of the anti-viral response.

Viral infection often activates a host cell’s intrinsic immune response resulting in the cellular secretion of cytokines, important host-defense molecules. These cytokines act on neighboring cells to make them less permissive to viral infection. Many of the mechanisms through which cytokines promote a less permissive cell state remain unclear. Our data indicate that treatment with the anti-viral cytokine TNFα induces substantial changes to cellular metabolic activity, including activating glucose metabolism. We find that these TNFα-induced metabolic changes are critical for TNFα to limit the replication of diverse viruses including Human Cytomegalovirus and two Coronaviruses, OC43 and SARS-CoV-2. Inhibition of glucose metabolism during TNFα treatment prevented the expression of a variety of known cellular anti-viral proteins. Collectively, our data indicate that cytokine-induced metabolic remodeling is an important component of TNFα’s ability to promote a less permissive cell state and raises further questions about the mechanisms through which specific cytokine-induced metabolic activities contribute to various aspects of anti-viral defense.

Lysine Acetylation/Deacetylation Modification of Immune-Related Molecules in Cancer Immunotherapy

As major post-translational modifications (PTMs), acetylation and deacetylation are significant factors in signal transmission and cellular metabolism, and are modulated by a dynamic process via two pivotal categories of enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs). In previous studies, dysregulation of lysine acetylation and deacetylation has been reported to be associated with the genesis and development of malignancy. Scientists have recently explored acetylation/deacetylation patterns and prospective cancer therapy techniques, and the FDA has approved four HDAC inhibitors (HDACi) to be used in clinical treatment. In the present review, the most recent developments in the area of lysine acetylation/deacetylation alteration in cancer immunotherapy were investigated. Firstly, a brief explanation of the acetylation/deacetylation process and relevant indispensable enzymes that participate therein is provided. Subsequently, a multitude of specific immune-related molecules involved in the lysine acetylation/deacetylation process are listed in the context of cancer, in addition to several therapeutic strategies associated with lysine acetylation/deacetylation modification in cancer immunotherapy. Finally, a number of prospective research fields related to cancer immunotherapy concepts are offered with detailed analysis. Overall, the present review may provide a reference for researchers in the relevant field of study, with the aim of being instructive and meaningful to further research as well as the selection of potential targets and effective measures for future cancer immunotherapy strategies.

Elevation of α-1,3 fucosylation promotes the binding ability of TNFR1 to TNF-α and contributes to osteoarthritic cartilage destruction and apoptosis

Background

Osteoarthritis (OA) is the most common form of arthritis and is characterized by the degradation of articular cartilage and inflammation of the synovial membrane. Fucosylation is an important feature of protein N/O-glycosylation and is involved in a variety of pathological processes, including inflammation and cancer. However, whether fucosylation impacts the OA pathological process is unknown.

Methods

Total proteins were extracted from cartilage samples obtained from patients with OA (n = 11) and OA rabbit models at different time points (n = 12). OA-associated abnormal glycopatterns were evaluated by lectin microarrays and lectin blots. The expression of fucosyltransferases involved in the synthesis of α-1,3 fucosylation was assessed by semi-qPCR. The synthesis of α-1,3 fucosylation mediated by FUT10 was interrupted by the transfection of siRNA, and the effect of α-1,3 fucosylation on OA-associated events was assessed. Then, immunoprecipitation and lectin blotting were used to investigate the relationship between the α-1,3 fucosylation level of tumor necrosis factor receptor superfamily member 1A (TNFR1) and OA. Finally, a TNFR1 antibody microarray was fabricated to evaluate the effect of α-1,3 fucosylation on the ability of TNFR1 to bind to tumor necrosis factor-α (TNF-α).

Results

Elevated α-1,3 fucosylation was observed in cartilage from OA patients, rabbit models, and chondrocytes induced by TNF-α (fold change> 2, p< 0.01). Our results and the GEO database indicated that the overexpression of FUT10 contributed to this alteration. Silencing the expression of FUT10 impaired the ability of TNFR1 to bind to TNF-α, impeded activation of the NF-κB and P38/JNK-MAPK pathways, and eventually retarded extracellular matrix (ECM) degradation, senescence, and apoptosis in chondrocytes exposed to TNF-α.

Conclusion

The elevation of α-1,3 fucosylation is not only a characteristic of OA but also impacts the OA pathological process. Our work provides a new positive feedback loop of “inflammation conditions/TNF-α/FUT10/α-1,3 fucosylation of TNFR1/NF-κB and P38/JNK-MAPK pathways/proinflammatory processes” that contributes to ECM degradation and chondrocyte apoptosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02776-z.

The basis of mink susceptibility to SARS-CoV-2 infection

Of all known airborne diseases in the twenty-first century, coronavirus disease 19 (COVID-19) has the highest infection and death rate. Over the past few decades, animal origin viral diseases, notably those of bats-linked, have increased many folds in humans with cross-species transmissions noted and the ongoing COVID-19 pandemic has emphasized the importance of understanding the evolution of natural hosts in response to viral pathogens. Cross-species transmissions are possible due to the possession of the angiotensin-converting enzyme 2 (ACE2) receptor in animals. ACE2 recognition by SARS-CoV-2 is a critical determinant of the host range, interspecies transmission, and viral pathogenesis. Thus, the phenomenon of breaking the cross-species barrier is mainly associated with mutations in the receptor-binding domain (RBD) of the spike (S) protein that interacts with ACE2. In this review, we raise the issue of cross-species transmission based on sequence alignment of S protein. Based on previous reports and our observations, we can conclude that the occurrence of one of two mutations D614G or Y453F is sufficient for infection of minks by SARS-CoV-2 from humans. Unfortunately, D614G is observed in the world’s most common line of virus B.1.1.7 and the latest SARS-CoV-2 variants B.1.617.1, B.1.617.2, and B.1.617.3 too.

Calreticulin Regulates β1-Integrin mRNA Stability in PC-3 Prostate Cancer Cells

Prostate cancer (PCa) is the major cause of cancer-related death among aging men worldwide. Recent studies have suggested that calreticulin (CRT), a multifunctional chaperon protein, may play an important role in the regulation of PCa tumorigenesis and progression. However, the underlying mechanisms are still unclear. Integrin is an important regulator of cancer metastasis. Our previous study demonstrated that in J82 bladder cancer cells, CRT affects integrin activity through FUBP-1-FUT-1-dependent fucosylation, rather than directly affecting the expression of β1-integrin itself. However, whether this regulatory mechanism is conserved among different cell types remains to be determined. Herein, we attempted to determine the effects of CRT on β1-integrin in human prostate cancer PC-3 cells. CRT expression was suppressed in PC-3 cells through siRNA treatment, and then the expression levels of FUT-1 and β1-integrin were monitored through RT-PCR. We found that knockdown of CRT expression in PC-3 cells significantly affected the expression of β1-integrin itself. In addition, the lower expression level of β1-integrin was due to affecting the mRNA stability. In contrast, FUT-1 expression level was not affected by knockdown of CRT. These results strongly suggested that CRT regulates cellular behavior differently in different cell types. We further confirmed that CRT directly binds to the 3′UTR of β1-integrin mRNA by EMSA and therefore affects its stability. The suppression of CRT expression also affects PC-3 cell adhesion to type I collagen substrate. In addition, the levels of total and activated β1-integrin expressed on cell surface were both significantly suppressed by CRT knockdown. Furthermore, the intracellular distribution of β1-integrin was also affected by lowering the expression of CRT. This change in distribution is not lysosomal nor proteosomal pathway-dependent. The treatment of fucosydase significantly affected the activation of surface β1-integrin, which is conserved among different cell types. These results suggested that CRT affects the expression of β1-integrin through distinct regulatory mechanisms.

Recent advances in the development of Aspergillus for protein production

Aspergillus had been widely used in the industrial production of recombinant proteins. In addition to the safety and broad substrate utilization spectrum, its efficient post-translational modification and strong protein secretion capacity have significant advantages for developing an excellent protein-producing cell factory in industrial production. However, the difficulties in genetic manipulation of Aspergillus and varying expression levels of different heterologous proteins hampered its further development and application. Recently, the development of CRISPR genome editing and high-throughput screening platforms has facilitated the Aspergillus development of a wide range of modifications and applications. Meanwhile, multi-omics analysis and multiplexed genetic engineering have promoted effective knowledge mining. This paper provides a comprehensive and updated review of these advances, including high-throughput screening, genome editing, protein expression modules, and fermentation optimization. It also highlights and discusses the latest significant progress, aiming to provide a practical guide for implementing Aspergillus as an efficient protein-producing cell factory.

Sensitive asprosin detection in clinical samples reveals serum/saliva correlation and indicates cartilage as source for serum asprosin

The C-terminal pro-fibrillin-1 propeptide asprosin is described as white adipose tissue derived hormone that stimulates rapid hepatic glucose release and activates hunger-promoting hypothalamic neurons. Numerous studies proposed correlations of asprosin levels with clinical parameters. However, the enormous variability of reported serum and plasma asprosin levels illustrates the need for sensitive and reliable detection methods in clinical samples. Here we report on newly developed biochemical methods for asprosin concentration and detection in several body fluids including serum, plasma, saliva, breast milk, and urine. Since we found that glycosylation impacts human asprosin detection we analyzed its glycosylation profile. Employing a new sandwich ELISA revealed that serum and saliva asprosin correlate strongly, depend on biological sex, and feeding status. To investigate the contribution of connective tissue-derived asprosin to serum levels we screened two cohorts with described cartilage turnover. Serum asprosin correlated with COMP, a marker for cartilage degradation upon running exercise and after total hip replacement surgery. This together with our finding that asprosin is produced by primary human chondrocytes and expressed in human cartilage suggests a contribution of cartilage to serum asprosin. Furthermore, we determined asprosin levels in breast milk, and urine, for the first time, and propose saliva asprosin as an accessible clinical marker for future studies.

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.

Cancer glycomics offers potential biomarkers and therapeutic targets in the framework of 3P medicine

Glycosylation is one of the most important post-translational modifications (PTMs) in a protein, and is the most abundant and diverse biopolymer in nature. Glycans are involved in multiple biological processes of cancer initiation and progression, including cell-cell interactions, cell-extracellular matrix interactions, tumor invasion and metastasis, tumor angiogenesis, and immune regulation. As an important biomarker, tumor-associated glycosylation changes have been extensively studied. This article reviews recent advances in glycosylation-based biomarker research, which is useful for cancer diagnosis and prognostic assessment. Truncated O-glycans, sialylation, fucosylation, and complex branched structures have been found to be the most common structural patterns in malignant tumors. In recent years, immunochemical methods, lectin recognition-based methods, mass spectrometry (MS)-related methods, and fluorescence imaging-based in situ methods have greatly promoted the discovery and application potentials of glycomic and glycoprotein biomarkers in various cancers. In particular, MS-based proteomics has significantly facilitated the comprehensive research of extracellular glycoproteins, increasing our understanding of their critical roles in regulating cellular activities. Predictive, preventive and personalized medicine (PPPM; 3P medicine) is an effective approach of early prediction, prevention and personalized treatment for different patients, and it is known as the new direction of medical development in the 21st century and represents the ultimate goal and highest stage of medical development. Glycosylation has been revealed to have new diagnostic, prognostic, and even therapeutic potentials. The purpose of glycosylation analysis and utilization of biology is to make a fundamental change in health care and medical practice, so as to lead medical research and practice into a new era of 3P medicine.

Proteomic Profiling of Astrocytic O-GlcNAc Transferase-Related Proteins in the Medial Prefrontal Cortex

The medial prefrontal cortex (mPFC), a key part of the brain networks that are closely related to the regulation of behavior, acts as a key regulator in emotion, social cognition, and decision making. Astrocytes are the majority cell type of glial cells, which play a significant role in a number of processes and establish a suitable environment for the functioning of neurons, including the brain energy metabolism. Astrocyte’s dysfunction in the mPFC has been implicated in various neuropsychiatric disorders. Glucose is a major energy source in the brain. In glucose metabolism, part of glucose is used to convert UDP-GlcNAc as a donor molecule for O-GlcNAcylation, which is controlled by a group of enzymes, O-GlcNAc transferase enzyme (OGT), and O-GlcNAcase (OGA). However, the role of O-GlcNAcylation in astrocytes is almost completely unknown. Our research showed that astrocytic OGT could influence the expression of proteins in the mPFC. Most of these altered proteins participate in metabolic processes, transferase activity, and biosynthetic processes. GFAP, an astrocyte maker, was increased after OGT deletion. These results provide a framework for further study on the role of astrocytic OGT/O-GlcNAcylation in the mPFC.

Analysis of the Role of N-Linked Glycosylation in Cell Surface Expression, Function, and Binding Properties of SARS-CoV-2 Receptor ACE2

Human angiotensin I-converting enzyme 2 (hACE2) is a type I transmembrane glycoprotein that serves as the major cell entry receptor for SARS-CoV and SARS-CoV-2. The viral spike (S) protein is required for the attachment to ACE2 and subsequent virus-host cell membrane fusion. Previous work has demonstrated the presence of N-linked glycans in ACE2. N-glycosylation is implicated in many biological activities, including protein folding, protein activity, and cell surface expression of biomolecules. However, the contribution of N-glycosylation to ACE2 function is poorly understood. Here, we examined the role of N-glycosylation in the activity and localization of two species with different susceptibility to SARS-CoV-2 infection, porcine ACE2 (pACE2) and hACE2. The elimination of N-glycosylation by tunicamycin (TM) treatment, or mutagenesis, showed that N-glycosylation is critical for the proper cell surface expression of ACE2 but not for its carboxiprotease activity. Furthermore, nonglycosylable ACE2 was localized predominantly in the endoplasmic reticulum (ER) and not at the cell surface. Our data also revealed that binding of SARS-CoV or SARS-CoV-2 S protein to porcine or human ACE2 was not affected by deglycosylation of ACE2 or S proteins, suggesting that N-glycosylation does not play a role in the interaction between SARS coronaviruses and the ACE2 receptor. Impairment of hACE2 N-glycosylation decreased cell-to-cell fusion mediated by SARS-CoV S protein but not that mediated by SARS-CoV-2 S protein. Finally, we found that hACE2 N-glycosylation is required for an efficient viral entry of SARS-CoV/SARS-CoV-2 S pseudotyped viruses, which may be the result of low cell surface expression of the deglycosylated ACE2 receptor. IMPORTANCE Understanding the role of glycosylation in the virus-receptor interaction is important for developing approaches that disrupt infection. In this study, we showed that deglycosylation of both ACE2 and S had a minimal effect on the spike-ACE2 interaction. In addition, we found that the removal of N-glycans of ACE2 impaired its ability to support an efficient transduction of SARS-CoV and SARS-CoV-2 S pseudotyped viruses. Our data suggest that the role of deglycosylation of ACE2 on reducing infection is likely due to a reduced expression of the viral receptor on the cell surface. These findings offer insight into the glycan structure and function of ACE2 and potentially suggest that future antiviral therapies against coronaviruses and other coronavirus-related illnesses involving inhibition of ACE2 recruitment to the cell membrane could be developed.