An atlas of O-linked glycosylation on peptide hormones reveals diverse biological roles

Understanding peptide hormones: from precursor proteins to bioactive molecules

Peptide hormones are fundamental regulators of biological processes involved in homeostasis regulation and are often dysregulated in endocrine diseases. Despite their biological significance and established therapeutic potential, there is still a gap in our knowledge of their processing and post-translational modifications, as well as in the technologies for their discovery and detection. In this review, we cover insights into the peptidome landscape, including the proteolytic processing and post-translational modifications of peptide hormones. Understanding the full landscape of peptide hormones and their modifications could provide insights into leveraging proteolytic mechanisms to identify novel peptides with therapeutic potential. Therefore, we also discuss the need for future research aiming at better predicting, detecting, and characterizing new peptides with biological activities.

Map of the Neuronal O-glycoproteome Reveal Driver Functions in the Regulated Secretory Pathway

Impairments in protein glycosylation, including O-GalNAc-type glycosylation, are linked to severe developmental disorders with prominent neurological involvement. However, the role of this glycosylation pathway at a cellular level is not yet fully understood. Here, we report a comprehensive map of GalNAc-type O-glycoproteins (>800) and O-glycosites (>4,000) from neuronal tissues and cell lines and identify abundant O-glycosites within major classes of proteins involved in neuroplasticity including axon guidance, membrane remodeling, and regulated vesicular secretion. Applying the map, we demonstrate that the regulated secretory pathway constitutes highly O-glycosylated proteins including Chromogranin A, a key player in dense core granulogenesis, and that correct O-glycosylation is important for its multimerization. Concurrently, genetically engineered neuronal cell lines deficient in O-glycosylation exhibit altered capacity for storing neurotransmitter noradrenaline and present enlarged neurotransmitter-containing dense core granules. Collectively, this map provides the foundation for uncovering critical roles for O-glycosylation in regulating neuroplasticity and provides evidence that dense core granule content is regulated by this pathway. Subjects: Granin, glycosylation, glycosaminoglycans, dense core granules (DCG), perineuronal net (PNN), mucin, central nervous system (CNS), neuron, neuroplasticity, neurotransmitter.

Total Chemical Synthesis of Glucagon Glycoforms Reveals the Remarkable Influence of Natural Glycosylation

Glycosylation plays a critical role in modulating protein and peptide properties, yet the impact of recently discovered natural mucin-type O-glycosylation on therapeutic peptides like glucagon remains underexplored due to challenges in obtaining homogeneous research samples. Here, we address this challenge by developing a streamlined multistep synthesis-one purification protocol, enabling the production of 21 glucagon glycoforms with systematically varied glycosylation patterns. Investigation of these glycoforms revealed a remarkable impact of natural glycosylation on two properties critical for glucagon: solubility increased by over 870-fold, and fibrillation was completely inhibited, even under stringent conditions, while biological activity in elevating blood glucose levels was preserved. Computational analyses indicated that sialylated glycans disrupt intermolecular associations in the solid state, enhancing solubility, and shift secondary structures from β-sheets to α-helices, mitigating fibrillation. These findings suggest that glycosylation may have evolved as a natural mechanism to optimize undesirable properties, offering valuable insights for the development of therapeutics based on glucagon and other proteins and peptides with similar challenges.

Sugar symphony: glycosylation in cancer metabolism and stemness

Glycosylation is a complex co-translational and post-translational modification (PTM) in eukaryotes that utilizes glycosyltransferases to generate a vast array of glycoconjugate structures. Recent studies have highlighted the role of glycans in regulating essential molecular, cellular, tissue, organ, and systemic biological processes with significant implications for human diseases, particularly cancer. The metabolic reliance of cancer, spanning tumor initiation, disease progression, and resistance to therapy, necessitates a range of uniquely altered cellular metabolic pathways. In addition, the intricate interplay between cell-intrinsic and -extrinsic mechanisms is exemplified by the communication between cancer cells, cancer stem cells (CSCs), cancer-associated fibroblasts (CAFs), and immune cells within the tumor microenvironment (TME). In this review article, we explore how differential glycosylation in cancer influences the metabolism and stemness features alongside new avenues in glycobiology.

A New Protractor Potentiates Glucagon-Like Peptide 1 with Slow-Release Depot and Long-Term Action

Bioactive peptides display a number of favorable features as therapeutics, but their usage is challenging due to the low metabolic stability and rapid renal clearance. The small-molecule protractor, which functions by the noncovalent binding with serum albumin and protection against systemic clearance, is an attractive tool to elongate peptides' half-life. Herein, we investigated coomassie brilliant blue (CBB) as a new protractor for the half-life extension of clinically relevant glucagon-like peptide 1 (GLP-1). A series of GLP-1 analogues differentiating with CBB linkers and acylation positions are described. One particularly interesting analogue (coomatide 13) exhibits sub-picomolar potency in vitro and long-term control of glucose homeostasis in mice. A protraction mechanism study reveals that CBB has a high affinity to albumin and pan-interaction with other matrix proteins, enabling to protract peptides in both systemic circulation and the subcutaneous depot. Our study demonstrates that the specific affinity to albumin is not a prerequisite for peptide protraction, and pan-binders might be advantageous.

Global characterization of mouse testis O-glycoproteome landscape during spermatogenesis

Protein O-glycosylation plays critical roles in sperm formation and maturation. However, detailed knowledge on the mechanisms involved is limited due to lacking characterization of O-glycoproteome of testicular germ cells. Here, we performed a systematic analysis of site-specific O-glycosylation in mouse testis, and established an O-glycoproteome map with 349 O-glycoproteins and 799 unambiguous O-glycosites. Moreover, we comprehensively investigated the distribution properties of O-glycosylation in testis and identified a region near the N-terminal of peptidase S1 domain that is susceptible to O-glycosylation. Interestingly, we found dynamic changes with an increase Tn and a decrease T structure from early to mature developmental stages. Notably, the importance of O-glycosylation was supported by its effects on the stability, cleavage, and interaction of acrosomal proteins. Collectively, these data illustrate the global properties of O-glycosylation in testis, providing insights and resources for future functional studies targeting O-glycosylation dysregulation in male infertility.

Peptide nanozymes: An emerging direction for functional enzyme mimics

The abundance of molecules on early Earth likely enabled a wide range of prebiotic chemistry, with peptides playing a key role in the development of early life forms and the evolution of metabolic pathways. Among peptides, those with enzyme-like activities occupy a unique position between peptides and enzymes, combining both structural flexibility and catalytic functionality. However, their full potential remains largely untapped. Further exploration of these enzyme-like peptides at the nanoscale could provide valuable insights into modern nanotechnology, biomedicine, and even the origins of life. Hence, this review introduces the groundbreaking concept of "peptide nanozymes (PepNzymes)", which includes single peptides exhibiting enzyme-like activities, peptide-based nanostructures with enzyme-like activities, and peptide-based nanozymes, thus enabling the investigation of biological phenomena at nanoscale dimensions. Through the rational design of enzyme-like peptides or their assembly with nanostructures and nanozymes, researchers have found or created PepNzymes capable of catalyzing a wide range of reactions. By scrutinizing the interactions between the structures and enzyme-like activities of PepNzymes, we have gained valuable insights into the underlying mechanisms governing enzyme-like activities. Generally, PepNzymes play a crucial role in biological processes by facilitating small-scale enzyme-like reactions, speeding up molecular oxidation-reduction, cleavage, and synthesis reactions, leveraging the functional properties of peptides, and creating a stable microenvironment, among other functions. These discoveries make PepNzymes useful for diagnostics, cellular imaging, antimicrobial therapy, tissue engineering, anti-tumor treatments, and more while pointing out opportunities. Overall, this research provides a significant journey of PepNzymes' potential in various biomedical applications, pushing them towards new advancements.

Fish-hunting cone snail disrupts prey's glucose homeostasis with weaponized mimetics of somatostatin and insulin

Venomous animals have evolved diverse molecular mechanisms to incapacitate prey and defend against predators. Most venom components disrupt nervous, locomotor, and cardiovascular systems or cause tissue damage. The discovery that certain fish-hunting cone snails use weaponized insulins to induce hypoglycemic shock in prey highlights a unique example of toxins targeting glucose homeostasis. Here, we show that, in addition to insulins, the deadly fish hunter, Conus geographus, uses a selective somatostatin receptor 2 (SSTR2) agonist that blocks the release of the insulin-counteracting hormone glucagon, thereby exacerbating insulin-induced hypoglycemia in prey. The native toxin, Consomatin nG1, exists in several proteoforms with a minimized vertebrate somatostatin-like core motif connected to a heavily glycosylated N-terminal region. We demonstrate that the toxin's N-terminal tail closely mimics a glycosylated somatostatin from fish pancreas and is crucial for activating the fish SSTR2. Collectively, these findings provide a stunning example of chemical mimicry, highlight the combinatorial nature of venom components, and establish glucose homeostasis as an effective target for prey capture.

Self-Promoted Glycosylation of Carbamoylated Peptides on Solid Phase

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

NeuroPep 2.0: An Updated Database Dedicated to Neuropeptide and Its Receptor Annotations

Neuropeptides not only work through nervous system but some of them also work peripherally to regulate numerous physiological processes. They are important in regulation of numerous physiological processes including growth, reproduction, social behavior, inflammation, fluid homeostasis, cardiovascular function, and energy homeostasis. The various roles of neuropeptides make them promising candidates for prospective therapeutics of different diseases. Currently, NeuroPep has been updated to version 2.0, it now holds 11,417 unique neuropeptide entries, which is nearly double of the first version of NeuroPep. When available, we collected information about the receptor for each neuropeptide entry and predicted the 3D structures of those neuropeptides without known experimental structure using AlphaFold2 or APPTEST according to the peptide sequence length. In addition, DeepNeuropePred and NeuroPred-PLM, two neuropeptide prediction tools developed by us recently, were also integrated into NeuroPep 2.0 to help to facilitate the identification of new neuropeptides. NeuroPep 2.0 is freely accessible at https://isyslab.info/NeuroPepV2/.

Cilia Provide a Platform for the Generation, Regulated Secretion, and Reception of Peptidergic Signals

Cilia are microtubule-based cellular projections that act as motile, sensory, and secretory organelles. These structures receive information from the environment and transmit downstream signals to the cell body. Cilia also release vesicular ectosomes that bud from the ciliary membrane and carry an array of bioactive enzymes and peptide products. Peptidergic signals represent an ancient mode of intercellular communication, and in metazoans are involved in the maintenance of cellular homeostasis and various other physiological processes and responses. Numerous peptide receptors, subtilisin-like proteases, the peptide-amidating enzyme, and bioactive amidated peptide products have been localized to these organelles. In this review, we detail how cilia serve as specialized signaling organelles and act as a platform for the regulated processing and secretion of peptidergic signals. We especially focus on the processing and trafficking pathways by which a peptide precursor from the green alga Chlamydomonas reinhardtii is converted into an amidated bioactive product-a chemotactic modulator-and released from cilia in ectosomes. Biochemical dissection of this complex ciliary secretory pathway provides a paradigm for understanding cilia-based peptidergic signaling in mammals and other eukaryotes.

Lignocellulosic biomass-based glycoconjugates for diverse biotechnological applications

Glycoconjugates are the ubiquitous components of mammalian cells, mainly synthesized by covalent bonds of carbohydrates to other biomolecules such as proteins and lipids, with a wide range of potential applications in novel vaccines, therapeutic peptides and antibodies (Ab). Considering the emerging developments in glycoscience, renewable production of glycoconjugates is of importance and lignocellulosic biomass (LCB) is a potential source of carbohydrates to produce synthetic glycoconjugates in a sustainable pathway. In this review, recent advances in glycobiology aiming on glycoconjugates production is presented together with the recent and cutting-edge advances in the therapeutic properties and application of glycoconjugates, including therapeutic glycoproteins, glycosaminoglycans (GAGs), and nutraceuticals, emphasizing the integral role of glycosylation in their function and efficacy. Special emphasis is given towards the potential exploration of carbon neutral feedstocks, in which LCB has an emerging role. Techniques for extraction and recovery of mono- and oligosaccharides from LCB are critically discussed and influence of the heterogeneous nature of the feedstocks and different methods for recovery of these sugars in the development of the customized glycoconjugates is explored. Although reports on the use of LCB for the production of glycoconjugates are scarce, this review sets clear that the potential of LCB as a source for the production of valuable glycoconjugates cannot be underestimated and encourages that future research should focus on refining the existing methodologies and exploring new approaches to fully realize the potential of LCB in glycoconjugate production.

PNA6, a Lactosyl Analogue of Angiotensin-(1-7), Reverses Pain Induced in Murine Models of Inflammation, Chemotherapy-Induced Peripheral Neuropathy, and Metastatic Bone Disease

Pain is the most significant impairment and debilitating challenge for patients with bone metastasis. Therefore, the primary objective of current therapy is to mitigate and prevent the persistence of pain. Thus, cancer-induced bone pain is described as a multifaceted form of discomfort encompassing both inflammatory and neuropathic elements. We have developed a novel non-addictive pain therapeutic, PNA6, that is a derivative of the peptide Angiotensin-(1-7) and binds the Mas receptor to decrease inflammation-related cancer pain. In the present study, we provide evidence that PNA6 attenuates inflammatory, chemotherapy-induced peripheral neuropathy (CIPN) and cancer pain confined to the long bones, exhibiting longer-lasting efficacious therapeutic effects. PNA6, Asp-Arg-Val-Tyr-Ile-His-Ser-(O-β-Lact)-amide, was successfully synthesized using solid phase peptide synthesis (SPPS). PNA6 significantly reversed inflammatory pain induced by 2% carrageenan in mice. A second murine model of platinum drug-induced painful peripheral neuropathy was established using oxaliplatin. Mice in the oxaliplatin-vehicle treatment groups demonstrated significant mechanical allodynia compared to the oxaliplatin-PNA6 treatment group mice. In a third study modeling a complex pain state, E0771 breast adenocarcinoma cells were implanted into the femur of female C57BL/6J wild-type mice to induce cancer-induced bone pain (CIBP). Both acute and chronic dosing of PNA6 significantly reduced the spontaneous pain behaviors associated with CIBP. These data suggest that PNA6 is a viable lead candidate for treating chronic inflammatory and complex neuropathic pain.

Towards clinical application of GlycA and GlycB for early detection of inflammation associated with (pre)diabetes and cardiovascular disease: recent evidence and updates

Cardiometabolic diseases are associated with low-grade inflammation early in life and persists into old age. The long latency period presents opportunities for early detection, lifestyle modification and intervention. However, the performance of conventional biomarker assays to detect low-grade inflammation has been variable, particularly for early-stage cardiometabolic disorder including prediabetes and subclinical atherosclerotic vascular inflammation. During the last decade, the application of nuclear magnetic resonance (NMR) spectroscopy for metabolic profiling of biofluids in translational and epidemiological research has advanced to a stage approaching clinical application. Proton (1H)-NMR profiling induces no destructible physical changes to specimens, and generates quantitative signals from deconvoluted spectra that are highly repeatable and reproducible. Apart from quantitative analysis of amino acids, lipids/lipoproteins, metabolic intermediates and small proteins, 1H-NMR technology is unique in being able to detect composite signals of acute-phase and low-grade inflammation indicated by glycosylated acetyls (GlycA) and N-acetylneuraminic acid (sialic acid) moieties (GlycB). Different from conventional immunoassays that target epitopes and are susceptible to conformational variation in protein structure and binding, GlycA and GlycB signals are stable over time, and maybe complementary as well as superior to high-sensitivity C-reactive protein and other inflammatory cytokines. Here we review the physicochemical principles behind 1H-NMR profiling of GlycA and GlycB, and the available evidence supporting their potential clinical application for the prediction of incident (pre)diabetes, cardiovascular disease, and adverse outcomes.

Characterization of natural peptides in Pheretima by integrating proteogenomics and label-free peptidomics

Pheretima, also called "earthworms", is a well-known animal-derived traditional Chinese medicine that is extensively used in over 50 Chinese patent medicines (CPMs) in Chinese Pharmacopoeia (2020 edition). However, its zoological origin is unclear, both in the herbal market and CPMs. In this study, a strategy for integrating in-house annotated protein databases constructed from close evolutionary relationship-sourced RNA sequencing data from public archival resources and various sequencing algorithms (restricted search, open search, and de novo) was developed to characterize the phenotype of natural peptides of three major commercial species of Pheretima, including Pheretima aspergillum (PA), Pheretima vulgaris (PV), and Metaphire magna (MM). We identified 10,477 natural peptides in the PA, 7,451 in PV, and 5,896 in MM samples. Five specific signature peptides were screened and then validated using synthetic peptides; these demonstrated robust specificity for the authentication of PA, PV, and MM. Finally, all marker peptides were successfully applied to identify the zoological origins of Brain Heart capsules and Xiaohuoluo pills, revealing the inconsistent Pheretima species used in these CPMs. In conclusion, our integrated strategy could be used for the in-depth characterization of natural peptides of other animal-derived traditional Chinese medicines, especially non-model species with poorly annotated protein databases.

Protein posttranslational modifications in health and diseases: Functions, regulatory mechanisms, and therapeutic implications

Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.

Glycosylation Analysis of Urinary Peptidome Highlights IGF2 Glycopeptides in Association with CKD

Chronic kidney disease (CKD) is prevalent in 10% of world’s adult population. The role of protein glycosylation in causal mechanisms of CKD progression is largely unknown. The aim of this study was to identify urinary O-linked glycopeptides in association to CKD for better characterization of CKD molecular manifestations. Urine samples from eight CKD and two healthy subjects were analyzed by CE-MS/MS and glycopeptides were identified by a specific software followed by manual inspection of the spectra. Distribution of the identified glycopeptides and their correlation with Age, eGFR and Albuminuria were evaluated in 3810 existing datasets. In total, 17 O-linked glycopeptides from 7 different proteins were identified, derived primarily from Insulin-like growth factor-II (IGF2). Glycosylation occurred at the surface exposed IGF2 Threonine 96 position. Three glycopeptides (DVStPPTVLPDNFPRYPVGKF, DVStPPTVLPDNFPRYPVG and DVStPPTVLPDNFPRYP) exhibited positive correlation with Age. The IGF2 glycopeptide (tPPTVLPDNFPRYP) showed a strong negative association with eGFR. These results suggest that with aging and deteriorating kidney function, alterations in IGF2 proteoforms take place, which may reflect changes in mature IGF2 protein. Further experiments corroborated this hypothesis as IGF2 increased plasma levels were observed in CKD patients. Protease predictions, considering also available transcriptomics data, suggest activation of cathepsin S with CKD, meriting further investigation.

Protein glycosylation in urine as a biomarker of diseases

Human body fluids have become an indispensable resource for clinical research, diagnosis and prognosis. Urine is widely used to discover disease-specific glycoprotein biomarkers because of its recurrently non-invasive collection and disease-indicating properties. While urine is an unstable fluid in that its composition changes with ingested nutrients and further as it is excreted through micturition, urinary proteins are more stable and their abnormal glycosylation is associated with diseases. It is known that aberrant glycosylation can define tumor malignancy and indicate disease initiation and progression. However, a thorough and translational survey of urinary glycosylation in diseases has not been performed. In this article, we evaluate the clinical applications of urine, introduce methods for urine glycosylation analysis, and discuss urine glycoprotein biomarkers. We emphasize the importance of mining urinary glycoproteins and searching for disease-specific glycosylation in various diseases (including cancer, neurodegenerative diseases, diabetes, and viral infections). With advances in mass spectrometry-based glycomics/glycoproteomics/glycopeptidomics, characterization of disease-specific glycosylation will optimistically lead to the discovery of disease-related urinary biomarkers with better sensitivity and specificity in the near future.

Recent advances in mass spectrometry analysis of neuropeptides

Due to their involvement in numerous biochemical pathways, neuropeptides have been the focus of many recent research studies. Unfortunately, classic analytical methods, such as western blots and enzyme-linked immunosorbent assays, are extremely limited in terms of global investigations, leading researchers to search for more advanced techniques capable of probing the entire neuropeptidome of an organism. With recent technological advances, mass spectrometry (MS) has provided methodology to gain global knowledge of a neuropeptidome on a spatial, temporal, and quantitative level. This review will cover key considerations for the analysis of neuropeptides by MS, including sample preparation strategies, instrumental advances for identification, structural characterization, and imaging; insightful functional studies; and newly developed absolute and relative quantitation strategies. While many discoveries have been made with MS, the methodology is still in its infancy. Many of the current challenges and areas that need development will also be highlighted in this review.

Primary Structure of Glycans by NMR Spectroscopy

Glycans, carbohydrate molecules in the realm of biology, are present as biomedically important glycoconjugates and a characteristic aspect is that their structures in many instances are branched. In determining the primary structure of a glycan, the sugar components including the absolute configuration and ring form, anomeric configuration, linkage(s), sequence, and substituents should be elucidated. Solution state NMR spectroscopy offers a unique opportunity to resolve all these aspects at atomic resolution. During the last two decades, advancement of both NMR experiments and spectrometer hardware have made it possible to unravel carbohydrate structure more efficiently. These developments applicable to glycans include, inter alia, NMR experiments that reduce spectral overlap, use selective excitations, record tilted projections of multidimensional spectra, acquire spectra by multiple receivers, utilize polarization by fast-pulsing techniques, concatenate pulse-sequence modules to acquire several spectra in a single measurement, acquire pure shift correlated spectra devoid of scalar couplings, employ stable isotope labeling to efficiently obtain homo- and/or heteronuclear correlations, as well as those that rely on dipolar cross-correlated interactions for sequential information. Refined computer programs for NMR spin simulation and chemical shift prediction aid the structural elucidation of glycans, which are notorious for their limited spectral dispersion. Hardware developments include cryogenically cold probes and dynamic nuclear polarization techniques, both resulting in enhanced sensitivity as well as ultrahigh field NMR spectrometers with a 1H NMR resonance frequency higher than 1 GHz, thus improving resolution of resonances. Taken together, the developments have made and will in the future make it possible to elucidate carbohydrate structure in great detail, thereby forming the basis for understanding of how glycans interact with other molecules.

Review A State of Natriuretic Peptide Deficiency

Measurement of natriuretic peptides (NPs) has proven its clinical value as biomarker, especially in the context of heart failure (HF). In contrast, a state partial NP deficiency appears integral to several conditions in which lower NP concentrations in plasma presage overt cardiometabolic disease. Here, obesity and type 2 diabetes have attracted considerable attention. Other factors - including age, sex, race, genetics, and diurnal regulation - affect the NP "armory" and may leave some individuals more prone to development of cardiovascular disease. The molecular maturation of NPs has also proven complex with highly variable O-glycosylation within the biosynthetic precursors. The relevance of this regulatory step in post-translational propeptide maturation has recently become recognized in biomarker measurement/interpretation and cardiovascular pathophysiology. An important proportion of people appear to have reduced effective net NP bioactivity in terms of receptor activation and physiological effects. The state of NP deficiency, then, both entails a potential for further biomarker development and could also offer novel pharmacological possibilities. Alleviating the state of NP deficiency before development of overt cardiometabolic disease in selected patients could be a future path for improving precision medicine.

Combining mass spectrometry and machine learning to discover bioactive peptides

Peptides play important roles in regulating biological processes and form the basis of a multiplicity of therapeutic drugs. To date, only about 300 peptides in human have confirmed bioactivity, although tens of thousands have been reported in the literature. The majority of these are inactive degradation products of endogenous proteins and peptides, presenting a needle-in-a-haystack problem of identifying the most promising candidate peptides from large-scale peptidomics experiments to test for bioactivity. To address this challenge, we conducted a comprehensive analysis of the mammalian peptidome across seven tissues in four different mouse strains and used the data to train a machine learning model that predicts hundreds of peptide candidates based on patterns in the mass spectrometry data. We provide in silico validation examples and experimental confirmation of bioactivity for two peptides, demonstrating the utility of this resource for discovering lead peptides for further characterization and therapeutic development.

Regulated processing and secretion of a peptide precursor in cilia

Cilia are sensory and secretory organelles that both receive information from the environment and transmit signals. Cilia-derived vesicles (ectosomes), formed by outward budding of the ciliary membrane, carry enzymes and other bioactive products; this process represents an ancient mode of regulated secretion. Peptidergic intercellular communication controls a wide range of physiological and behavioral responses and occurs throughout eukaryotes. The Chlamydomonas reinhardtii genome encodes what appear to be numerous prepropeptides and enzymes homologous to those used to convert metazoan prepropeptides into bioactive peptide products. Since C. reinhardtii, a green alga, lack the dense core vesicles in which metazoan peptides are processed and stored, we explored the hypothesis that propeptide processing and secretion occur through the regulated release of ciliary ectosomes. A synthetic peptide (GATI-amide) that could be generated from a 91-kDa peptide precursor (proGATI) serves as a chemotactic modulator, attracting minus gametes while repelling plus gametes. Here we dissect the processing pathway that leads to formation of an amidated peptidergic sexual signal specifically on the ciliary ectosomes of plus gametes. Unlike metazoan propeptides, modeling studies identified stable domains in proGATI. Mass spectrometric analysis of a potential prohormone convertase and the amidated proGATI-derived products found in cilia and mating ectosomes link endoproteolytic cleavage to ectosome entry. Extensive posttranslational modification of proGATI confers stability to its amidated product. Analysis of this pathway affords insight into the evolution of peptidergic signaling; this will facilitate studies of the secretory functions of metazoan cilia.

Mass Spectrometry Approaches Empowering Neuropeptide Discovery and Therapeutics

The discovery of insulin in the early 1900s ushered in the era of research related to peptides acting as hormones and neuromodulators, among other regulatory roles. These essential gene products are found in all organisms, from the most primitive to the most evolved, and carry important biologic information that coordinates complex physiology and behavior; their misregulation has been implicated in a variety of diseases. The evolutionary origins of at least 30 neuropeptide signaling systems have been traced to the common ancestor of protostomes and deuterostomes. With the use of relevant animal models and modern technologies, we can gain mechanistic insight into orthologous and paralogous endogenous peptides and translate that knowledge into medically relevant insights and new treatments. Groundbreaking advances in medicine and basic science influence how signaling peptides are defined today. The precise mechanistic pathways for over 100 endogenous peptides in mammals are now known and have laid the foundation for multiple drug development pipelines. Peptide biologics have become valuable drugs due to their unique specificity and biologic activity, lack of toxic metabolites, and minimal undesirable interactions. This review outlines modern technologies that enable neuropeptide discovery and characterization, and highlights lessons from nature made possible by neuropeptide research in relevant animal models that is being adopted by the pharmaceutical industry. We conclude with a brief overview of approaches/strategies for effective development of peptides as drugs. SIGNIFICANCE STATEMENT: Neuropeptides, an important class of cell-cell signaling molecules, are involved in maintaining a range of physiological functions. Since the discovery of insulin's activity, over 100 bioactive peptides and peptide analogs have been used as therapeutics. Because these are complex molecules not easily predicted from a genome and their activity can change with subtle chemical modifications, mass spectrometry (MS) has significantly empowered peptide discovery and characterization. This review highlights contributions of MS-based research towards the development of therapeutic peptides.

Biochemistry of the Endocrine Heart

Simple Summary

Besides being a muscle and an electrochemically active organ, the heart is a true endocrine organ. As endocrine cells, cardiac myocytes possess all the needed chemical necessities for translation, post-translational modifications, and complex peptide proteolysis. In addition, intracellular granules in the cells contain not only peptides destined for secretion but also important granin molecules involved in maintaining a regulated secretory pathway. In this review, we highlight the biochemical phenotype of the endocrine heart, recapitulating that the cardiac myocytes are truly and fully capable endocrine cells.

Abstract

Production and release of natriuretic peptides and other vasoactive peptides are tightly regulated in mammalian physiology and involved in cardiovascular homeostasis. As endocrine cells, the cardiac myocytes seem to possess almost all known chemical necessities for translation, post-translational modifications, and complex peptide proteolysis. In several ways, intracellular granules in the cells contain not only peptides destined for secretion but also important granin molecules involved in maintaining a regulated secretory pathway. In this review, we will highlight the biochemical phenotype of the endocrine heart recapitulating that the cardiac myocytes are capable endocrine cells. Understanding the basal biochemistry of the endocrine heart in producing and secreting peptides to circulation could lead to new discoveries concerning known peptide products as well as hitherto unidentified cardiac peptide products. In perspective, studies on natriuretic peptides in the heart have shown that the post-translational phase of gene expression is not only relevant for human physiology but may prove implicated also in the development and, perhaps one day, cure of human cardiovascular disease.

Integrated Chemoenzymatic Approach to Streamline the Assembly of Complex Glycopeptides in the Liquid Phase

Glycosylation of proteins is a complicated post-translational modification. Despite the significant progress in glycoproteomics, accurate functions of glycoproteins are still ambiguous owing to the difficulty in obtaining homogeneous glycopeptides or glycoproteins. Here, we describe a streamlined chemoenzymatic method to prepare complex glycopeptides by integrating hydrophobic tag-supported chemical synthesis and enzymatic glycosylations. The hydrophobic tag is utilized to facilitate peptide chain elongation in the liquid phase and expeditious product separation. After removal of the tag, a series of glycans are installed on the peptides via efficient glycosyltransferase-catalyzed reactions. The general applicability and robustness of this approach are exemplified by efficient preparation of 16 well-defined SARS-CoV-2 O-glycopeptides, 4 complex MUC1 glycopeptides, and a 31-mer glycosylated glucagon-like peptide-1. Our developed approach will open up a new range of easy access to various complex glycopeptides of biological importance.

Corin: A Key Mediator in Sodium Homeostasis, Vascular Remodeling, and Heart Failure

Simple Summary

Atrial natriuretic peptide (ANP) is an important hormone that regulates many physiological and pathological processes, including electrolyte and body fluid balance, blood volume and pressure, cardiac channel activity and function, inflammatory response, lipid metabolism, and vascular remodeling. Corin is a transmembrane serine protease that activates ANP. Variants in the CORIN gene are associated with cardiovascular disease, including hypertension, cardiac hypertrophy, atrial fibrillation, heart failure, and preeclampsia. The current data indicate a key role of corin-mediated ANP production and signaling in the maintenance of cardiovascular homeostasis. In this review, we discuss the latest findings regarding the molecular and cellular mechanisms underlying the role of corin in sodium homeostasis, uterine spiral artery remodeling, and heart failure.

Abstract

Atrial natriuretic peptide (ANP) is a crucial element of the cardiac endocrine function that promotes natriuresis, diuresis, and vasodilation, thereby protecting normal blood pressure and cardiac function. Corin is a type II transmembrane serine protease that is highly expressed in the heart, where it converts the ANP precursor to mature ANP. Corin deficiency prevents ANP activation and causes hypertension and heart disease. In addition to the heart, corin is expressed in other tissues, including those of the kidney, skin, and uterus, where corin-mediated ANP production and signaling act locally to promote sodium excretion and vascular remodeling. These results indicate that corin and ANP function in many tissues via endocrine and autocrine mechanisms. In heart failure patients, impaired natriuretic peptide processing is a common pathological mechanism that contributes to sodium and body fluid retention. In this review, we discuss most recent findings regarding the role of corin in non-cardiac tissues, including the kidney and skin, in regulating sodium homeostasis and body fluid excretion. Moreover, we describe the molecular mechanisms underlying corin and ANP function in supporting orderly cellular events in uterine spiral artery remodeling. Finally, we assess the potential of corin-based approaches to enhance natriuretic peptide production and activity as a treatment of heart failure.

New Opportunities in Glycan Engineering for Therapeutic Proteins

Glycans as sugar polymers are important metabolic, structural, and physiological regulators for cellular and biological functions. They are often classified as critical quality attributes to antibodies and recombinant fusion proteins, given their impacts on the efficacy and safety of biologics drugs. Recent reports on the conjugates of N-acetyl-galactosamine and mannose-6-phosphate for lysosomal degradation, Fab glycans for antibody diversification, as well as sialylation therapeutic modulations and O-linked applications, have been fueling the continued interest in glycoengineering. The current advancements of the human glycome and the development of a comprehensive network in glycosylation pathways have presented new opportunities in designing next-generation therapeutic proteins.

Multiplexed Assay to Quantify the PP-Fold Family of Peptides in Human Plasma Using Microflow Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND

Peptide Tyr-Tyr (PYY1-36), pancreatic polypeptide (PP1-36) and neuropeptide Y (NPY1-36) constitute the PP-fold family of peptides that is involved in metabolic regulation. Very low plasma concentrations and cleavage into active 3-36 fragments challenge bioanalytical assays used for the quantification of these peptides.

METHODS

We developed a multiplexed isotopic dilution assay to quantify PYY1-36, PP1-36, and NPY1-36 and their dipeptidyl peptidase-4 (DPP4)-derived metabolites PYY3-36, PP3-36 and NPY3-36. All peptides were immunocaptured from plasma using a monoclonal antibody and quantified by micro-ultra-HPLC-MS/MS. Blood samples from healthy volunteers were collected fasting and 30 min after nutrient stimulation. Method comparison was performed with commercial immunoassays.

RESULTS

Linearity was shown in the measured intervals (r2 > 0.99). The lower limit of quantification (LLOQ) with a CV at 20% was 1.5 pM for PYY1-36 and PYY3-36, 3.0 pM for PP1-36 and PP3-36, 0.8 pM for NPY1-36 and 0.5 pM for NPY3-36. In all cases, intra- and inter-assay bias and imprecision were <21%. Pre-analytical stability required addition of a protease inhibitor cocktail. Physiological concentrations of PYY3-36, NPY3-36, PP1-36 and PP3-36 were above the LLOQ in 43% to 100% of the samples. PYY1-36 and NPY1-36 were above the LLOQ in 9% and 0% of the samples, respectively. Immunoassays showed higher concentrations of measurands and poor agreement when compared with micro-UHPLC-MS/MS.

CONCLUSIONS

The assay allowed for specific multiplexed analysis of the PP-fold family of peptides and their DPP4-cleaved fragments in a single sample, thereby offering new perspectives to study the role and therapeutic potential of these essential peptide hormones in health and metabolic disease.

An Overview of Glycosylation and its Impact on Cardiovascular Health and Disease

The cardiovascular system is a complex and well-organized system in which glycosylation plays a vital role. The heart and vascular wall cells are constituted by an array of specific receptors; most of them are N- glycosylated and mucin-type O-glycosylated. There are also intracellular signaling pathways regulated by different post-translational modifications, including O-GlcNAcylation, which promote adequate responses to extracellular stimuli and signaling transduction. Herein, we provide an overview of N-glycosylation and O-glycosylation, including O-GlcNAcylation, and their role at different levels such as reception of signal, signal transduction, and exogenous molecules or agonists, which stimulate the heart and vascular wall cells with effects in different conditions, like the physiological status, ischemia/reperfusion, exercise, or during low-grade inflammation in diabetes and aging. Furthermore, mutations of glycosyltransferases and receptors are associated with development of cardiovascular diseases. The knowledge on glycosylation and its effects could be considered biochemical markers and might be useful as a therapeutic tool to control cardiovascular diseases.

Discovery and Development of Promiscuous O-Glycan Hydrolases for Removal of Intact Sialyl T-Antigen

Mucin-type O-glycosylation (O-glycosylation) is a common post-translational modification that confers distinct biophysical properties to proteins and plays crucial roles in intercellular signaling. Yet, despite the importance of O-glycans, relatively few tools exist for their analysis and modification. In particular, there is a need for enzymes that can cleave the wide range of O-glycan structures found on protein surfaces, to facilitate glycan profiling and editing. Through functional metagenomic screening of the human gut microbiome, we discovered endo-O-glycan hydrolases from CAZy family GH101 that are capable of slowly cleaving the intact sialyl T-antigen trisaccharide (a ubiquitous O-glycan structure in humans) in addition to their primary activity against the T-antigen disaccharide. We then further explored this sequence space through phylogenetic profiling and analysis of representative enzymes, revealing large differences in the levels of this promiscuous activity between enzymes within the family. Through structural and sequence analysis, we identified active site residues that modulate specificity. Through subsequent rational protein engineering, we improved the activity of an enzyme identified by phylogenetic profiling sufficiently that substantial removal of the intact sialyl T-antigen from proteins could be readily achieved. Our best sialyl T-antigen hydrolase mutant, SpGH101 Q868G, is further shown to function on a number of proteins, tissues, and cells. Access to this enzyme opens up improved methodologies for unraveling the glycan code.

Investigation of sequon engineering for improved O-glycosylation by the human polypeptide N-acetylgalactosaminyl transferase T2 isozyme and two orthologues

We have been developing bacterial expression systems for human mucin-type O-glycosylation on therapeutic proteins, which is initiated by the addition of α-linked GalNAc to serine or threonine residues by enzymes in the GT-27 family of glycosyltransferases. Substrate preference across different isoforms of this enzyme is influenced by isoform-specific amino acid sequences at the site of glycosylation, which we have exploited to engineer production of Core 1 glycan structures in bacteria on human therapeutic proteins. Using RP-HPLC with a novel phenyl bonded phase to resolve intact protein glycoforms, the effect of sequon mutation on O-glycosylation initiation was examined through in vitro modification of the naturally O-glycosylated human interferon α-2b, and a sequon engineered human growth hormone. As part of the development of our glycan engineering in the bacterial expression system we are surveying various orthologues of critical enzymes to ensure complete glycosylation. Here we present an in vitro enzyme kinetic profile of three related GT-27 orthologues on natural and engineered sequons in recombinant human interferon α2b and human growth hormone where we show a significant change in kinetic properties with the amino acid changes. It was found that optimizing the protein substrate amino acid sequence using Isoform Specific O-Glycosylation Prediction (ISOGlyP, http://isoglyp.utep.edu/index.php) resulted in a measurable increase in kcat/KM, thus improving glycosylation efficiency. We showed that the Drosophila orthologue showed superior activity with our human growth hormone designed sequons compared with the human enzyme.

The Major Peanut Allergen Ara h 2 Produced in Nicotiana benthamiana Contains Hydroxyprolines and Is a Viable Alternative to the E. Coli Product in Allergy Diagnosis

Peanut allergy is a potentially life-threatening disease that is mediated by allergen-specific immunoglobulin E (IgE) antibodies. The major peanut allergen Ara h 2, a 2S albumin seed storage protein, is one of the most dangerous and potent plant allergens. Ara h 2 is posttranslationally modified to harbor four disulfide bridges and three hydroxyprolines. These hydroxyproline residues are required for optimal IgE-binding to the DPYSPOHS motifs representing an immunodominant IgE epitope. So far, recombinant Ara h 2 has been produced in Escherichia coli, Lactococcus lactis, Trichoplusia ni insect cell, and Chlamydomonas reinhardtii chloroplast expression systems, which were all incapable of proline hydroxylation. However, molecular diagnosis of peanut allergy is performed using either natural or E. coli-produced major peanut allergens. As IgE from the majority of patients is directed to Ara h 2, it is of great importance that the recombinant Ara h 2 harbors all of its eukaryotic posttranslational modifications. We produced hydroxyproline-containing and correctly folded Ara h 2 in the endoplasmic reticulum of leaf cells of Nicotiana benthamiana plants, using the plant virus-based magnICON® transient expression system with a yield of 200 mg/kg fresh biomass. To compare prokaryotic with eukaryotic expression methods, Ara h 2 was expressed in E. coli together with the disulfide-bond isomerase DsbC and thus harbored disulfide bridges but no hydroxyprolines. The recombinant allergens from N. benthamiana and E. coli were characterized and compared to the natural Ara h 2 isolated from roasted peanuts. Natural Ara h 2 outperformed both recombinant proteins in IgE-binding and activation of basophils via IgE cross-linking, the latter indicating the potency of the allergen. Interestingly, significantly more efficient IgE cross-linking by the N. benthamiana-produced allergen was observed in comparison to the one induced by the E. coli product. Ara h 2 from N. benthamiana plants displayed a higher similarity to the natural allergen in terms of basophil activation due to the presence of hydroxyproline residues, supporting so far published data on their contribution to the immunodominant IgE epitope. Our study advocates the use of N. benthamiana plants instead of prokaryotic expression hosts for the production of the major peanut allergen Ara h 2.

Synthesis, Physicochemical Characterization, In Vitro 2D/3D Human Cell Culture, and In Vitro Aerosol Dispersion Performance of Advanced Spray Dried and Co-Spray Dried Angiotensin (1-7) Peptide and PNA5 with Trehalose as Microparticles/Nanoparticles for Targeted Respiratory Delivery as Dry Powder Inhalers

The peptide hormone Angiotensin (1-7), Ang (1-7) or (Asp-Arg-Val-Tyr-Ile-His-Pro), is an essential component of the renin-angiotensin system (RAS) peripherally and is an agonist of the Mas receptor centrally. Activation of this receptor in the CNS stimulates various biological activities that make the Ang (1-7)/MAS axis a novel therapeutic approach for the treatment of many diseases. The related O-linked glycopeptide, Asp-Arg-Val-Tyr-Ile-His-Ser-(O-β-D-Glc)-amide (PNA5), is a biousian revision of the native peptide hormone Ang (1-7) and shows enhanced stability in vivo and greater levels of brain penetration. We have synthesized the native Ang (1-7) peptide and the glycopeptide, PNA5, and have formulated them for targeted respiratory delivery as inhalable dry powders. Solid phase peptide synthesis (SPPS) successfully produced Ang (1-7) and PNA5. Measurements of solubility and lipophilicity of raw Ang (1-7) and raw PNA5 using experimental and computational approaches confirmed that both the peptide and glycopeptide have high-water solubility and are amphipathic. Advanced organic solution spray drying was used to engineer the particles and produce spray-dried powders (SD) of both the peptide and the glycopeptide, as well as co-spray-dried powders (co-SD) with the non-reducing sugar and pharmaceutical excipient, trehalose. The native peptide, glycopeptide, SD, and co-SD powders were comprehensively characterized, and exhibited distinct glass transitions (Tg) consistent with the amorphous glassy state formation with Tgs that are compatible with use in vivo. The homogeneous particles displayed small sizes in the nanometer size range and low residual water content in the solid-state. Excellent aerosol dispersion performance with a human DPI device was demonstrated. In vitro human cell viability assays showed that Ang (1-7) and PNA5 are biocompatible and safe for different human respiratory and brain cells.

Expanding the Chondroitin Sulfate Glycoproteome - But How Far?

Chondroitin sulfate proteoglycans (CSPGs) are found at cell surfaces and in connective tissues, where they interact with a multitude of proteins involved in various pathophysiological processes. From a methodological perspective, the identification of CSPGs is challenging, as the identification requires the combined sequencing of specific core proteins, together with the characterization of the CS polysaccharide modification(s). According to the current notion of CSPGs, they are often considered in relation to a functional role in which a given proteoglycan regulates a specific function in cellular physiology. Recent advances in glycoproteomic methods have, however, enabled the identification of numerous novel chondroitin sulfate core proteins, and their glycosaminoglycan attachment sites, in humans and in various animal models. In addition, these methods have revealed unexpected structural complexity even in the linkage regions. These findings indicate that the number and structural complexity of CSPGs are much greater than previously perceived. In light of these findings, the prospect of finding additional CSPGs, using improved methods for structural and functional characterizations, and studying novel sample matrices in humans and in animal models is discussed. Further, as many of the novel CSPGs are found in low abundance and with not yet assigned functions, these findings may challenge the traditional notion of defining proteoglycans. Therefore, the concept of proteoglycans is considered, discussing whether "a proteoglycan" should be defined mainly on the basis of an assigned function or on the structural evidence of its existence.

Global functions of O-glycosylation: promises and challenges in O-glycobiology

Mucin type O-glycosylation is one of the most diverse types of glycosylation, playing essential roles in tissue development and homeostasis. In complex organisms, O-GalNAc glycans comprise a substantial proportion of the glycocalyx, with defined functions in hemostatic, gastrointestinal, and respiratory systems. Furthermore, O-GalNAc glycans are important players in host-microbe interactions, and changes in O-glycan composition are associated with certain diseases and metabolic conditions, which in some instances can be used for diagnosis or therapeutic intervention. Breakthroughs in O-glycobiology have gone hand in hand with the development of new technologies, such as advancements in mass spectrometry, as well as facilitation of genetic engineering in mammalian cell lines. High-throughput O-glycoproteomics have enabled us to draw a comprehensive map of O-glycosylation, and mining this information has supported the definition and confirmation of functions related to site-specific O-glycans. This includes protection from proteolytic cleavage, as well as modulation of binding affinity or receptor function. Yet, there is still much to discover, and among the important next challenges will be to define the context-dependent functions of O-glycans in different stages of cellular differentiation, cellular metabolism, host-microbiome interactions, and in disease. In this review, we present the achievements and the promises in O-GalNAc glycobiology driven by technological advances in analytical methods, genetic engineering, and systems biology.

Developing mass spectrometry for the quantitative analysis of neuropeptides

INTRODUCTION

Neuropeptides are signaling molecules originating in the neuroendocrine system that can act as neurotransmitters and hormones in many biochemical processes. Their exact function is difficult to characterize, however, due to dependence on concentration, post-translational modifications, and the presence of other comodulating neuropeptides. Mass spectrometry enables sensitive, accurate, and global peptidomic analyses that can profile neuropeptide expression changes to understand their roles in many biological problems, such as neurodegenerative disorders and metabolic function.

AREAS COVERED

We provide a brief overview of the fundamentals of neuropeptidomic research, limitations of existing methods, and recent progress in the field. This review is focused on developments in mass spectrometry and encompasses labeling strategies, post-translational modification analysis, mass spectrometry imaging, and integrated multi-omic workflows, with discussion emphasizing quantitative advancements.

EXPERT OPINION

Neuropeptidomics is critical for future clinical research with impacts in biomarker discovery, receptor identification, and drug design. While advancements are being made to improve sensitivity and accuracy, there is still room for improvement. Better quantitative strategies are required for clinical analyses, and these methods also need to be amenable to mass spectrometry imaging, post-translational modification analysis, and multi-omics to facilitate understanding and future treatment of many diseases.

PAM: diverse roles in neuroendocrine cells, cardiomyocytes, and green algae

Our understanding of the ways in which peptides are used for communication in the nervous and endocrine systems began with the identification of oxytocin, vasopressin, and insulin, each of which is stored in electron-dense granules, ready for release in response to an appropriate stimulus. For each of these peptides, entry of its newly synthesized precursor into the ER lumen is followed by transport through the secretory pathway, exposing the precursor to a sequence of environments and enzymes that produce the bioactive products stored in mature granules. A final step in the biosynthesis of many peptides is C-terminal amidation by peptidylglycine α-amidating monooxygenase (PAM), an ascorbate- and copper-dependent membrane enzyme that enters secretory granules along with its soluble substrates. Biochemical and cell biological studies elucidated the highly conserved mechanism for amidated peptide production and raised many questions about PAM trafficking and the effects of PAM on cytoskeletal organization and gene expression. Phylogenetic studies and the discovery of active PAM in the ciliary membranes of Chlamydomonas reinhardtii, a green alga lacking secretory granules, suggested that a PAM-like enzyme was present in the last eukaryotic common ancestor. While the catalytic features of human and C. reinhardtii PAM are strikingly similar, the trafficking of PAM in C. reinhardtii and neuroendocrine cells and secretion of its amidated products differ. A comparison of PAM function in neuroendocrine cells, atrial myocytes, and C. reinhardtii reveals multiple ways in which altered trafficking allows PAM to accomplish different tasks in different species and cell types.

Chemical (neo)glycosylation of biological drugs

Biological drugs, specifically proteins and peptides, are a privileged class of medicinal agents and are characterized with high specificity and high potency of therapeutic activity. However, biologics are fragile and require special care during storage, and are often modified to optimize their pharmacokinetics in terms of proteolytic stability and blood residence half-life. In this review, we showcase glycosylation as a method to optimize biologics for storage and application. Specifically, we focus on chemical glycosylation as an approach to modify biological drugs. We present case studies that illustrate the success of this methodology and specifically address the highly important question: does connectivity within the glycoconjugate have to be native or not? We then present the innovative methods of chemical glycosylation of biologics and specifically highlight the emerging and established protecting group-free methodologies of glycosylation. We discuss thermodynamic origins of protein stabilization via glycosylation, and analyze in detail stabilization in terms of proteolytic stability, aggregation upon storage and/or heat treatment. Finally, we present a case study of protein modification using sialic acid-containing glycans to avoid hepatic clearance of biological drugs. This review aims to spur interest in chemical glycosylation as a facile, powerful tool to optimize proteins and peptides as medicinal agents.

Mammalian Neuropeptides as Modulators of Microbial Infections: Their Dual Role in Defense versus Virulence and Pathogenesis

The regulation of infection and inflammation by a variety of host peptides may represent an evolutionary failsafe in terms of functional degeneracy and it emphasizes the significance of host defense in survival. Neuropeptides have been demonstrated to have similar antimicrobial activities to conventional antimicrobial peptides with broad-spectrum action against a variety of microorganisms. Neuropeptides display indirect anti-infective capacity via enhancement of the host’s innate and adaptive immune defense mechanisms. However, more recently concerns have been raised that some neuropeptides may have the potential to augment microbial virulence. In this review we discuss the dual role of neuropeptides, perceived as a double-edged sword, with antimicrobial activity against bacteria, fungi, and protozoa but also capable of enhancing virulence and pathogenicity. We review the different ways by which neuropeptides modulate crucial stages of microbial pathogenesis such as adhesion, biofilm formation, invasion, intracellular lifestyle, dissemination, etc., including their anti-infective properties but also detrimental effects. Finally, we provide an overview of the efficacy and therapeutic potential of neuropeptides in murine models of infectious diseases and outline the intrinsic host factors as well as factors related to pathogen adaptation that may influence efficacy.

Deciphering cell-cell interactions and communication from gene expression

Cell-cell interactions orchestrate organismal development, homeostasis and single-cell functions. When cells do not properly interact or improperly decode molecular messages, disease ensues. Thus, the identification and quantification of intercellular signalling pathways has become a common analysis performed across diverse disciplines. The expansion of protein-protein interaction databases and recent advances in RNA sequencing technologies have enabled routine analyses of intercellular signalling from gene expression measurements of bulk and single-cell data sets. In particular, ligand-receptor pairs can be used to infer intercellular communication from the coordinated expression of their cognate genes. In this Review, we highlight discoveries enabled by analyses of cell-cell interactions from transcriptomic data and review the methods and tools used in this context.

Processing-independent analysis (PIA): a method for quantitation of the total peptide-gene expression

The translational product of protein-coding genes undergoes extensive posttranslational modifications. The modifications ensure an increased molecular and functional diversity at protein- and peptide-level. Prohormones are small pro-proteins that are expressed in many cell types, for instance endocrine cells, immune cells, myocytes and neurons. Here they mature to bioactive peptides (cytokines, hormones, growth factors, and neurotransmitters) that are released from the cells in an often regulated manner. The posttranslational processing of prohormones is cell-specific, however, and may vary during evolution and disease. Therefore, it is often inadequate to measure just a single peptide fragment as marker of endocrine, immune, and neuronal functions. In order to meet this challenge, we developed years back a simple "processing-independent analysis" (PIA) for accurate quantification of the total pro-protein product - irrespective of the degree and nature of the posttranslational processing. This review provides an overview of the PIA principle and describes examples of PIA results in different peptide systems.

Mucin-Type O-GalNAc Glycosylation in Health and Disease

Mucin-type GalNAc O-glycosylation is one of the most abundant and unique post-translational modifications. The combination of proteome-wide mapping of GalNAc O-glycosylation sites and genetic studies with knockout animals and genome-wide analyses in humans have been instrumental in our understanding of GalNAc O-glycosylation. Combined, such studies have revealed well-defined functions of O-glycans at single sites in proteins, including the regulation of pro-protein processing and proteolytic cleavage, as well as modulation of receptor functions and ligand binding. In addition to isolated O-glycans, multiple clustered O-glycans have an important function in mammalian biology by providing structural support and stability of mucins essential for protecting our inner epithelial surfaces, especially in the airways and gastrointestinal tract. Here the many O-glycans also provide binding sites for both endogenous and pathogen-derived carbohydrate-binding proteins regulating critical developmental programs and helping maintain epithelial homeostasis with commensal organisms. Finally, O-glycan changes have been identified in several diseases, most notably in cancer and inflammation, where the disease-specific changes can be used for glycan-targeted therapies. This chapter will review the biosynthesis, the biology, and the translational perspectives of GalNAc O-glycans.

The half-life of the bone-derived hormone osteocalcin is regulated through O-glycosylation in mice, but not in humans

Osteocalcin (OCN) is an osteoblast-derived hormone with pleiotropic physiological functions. Like many peptide hormones, OCN is subjected to post-translational modifications (PTMs) which control its activity. Here, we uncover O-glycosylation as a novel PTM present on mouse OCN and occurring on a single serine (S8) independently of its carboxylation and endoproteolysis, two other PTMs regulating this hormone. We also show that O-glycosylation increases OCN half-life in plasma ex vivo and in the circulation in vivo. Remarkably, in human OCN (hOCN), the residue corresponding to S8 is a tyrosine (Y12), which is not O-glycosylated. Yet, the Y12S mutation is sufficient to O-glycosylate hOCN and to increase its half-life in plasma compared to wildtype hOCN. These findings reveal an important species difference in OCN regulation, which may explain why serum concentrations of OCN are higher in mouse than in human.

Bones provide support and protection for organs in the body. However, over the last 15 years researchers have discovered that bones also release chemicals known as hormones, which can travel to other parts of the body and cause an effect. The cells responsible for making bone, known as osteoblasts, produce a hormone called osteocalcin which communicates with a number of different organs, including the pancreas and brain.

When osteocalcin reaches the pancreas, it promotes the release of another hormone called insulin which helps regulate the levels of sugar in the blood. Osteocalcin also travels to other organs such as muscle, where it helps to degrade fats and sugars that can be converted into energy. It also has beneficial effects on the brain, and has been shown to aid memory and reduce depression.

Osteocalcin has largely been studied in mice where levels are five to ten times higher than in humans. But it is unclear why this difference exists or how it alters the role of osteocalcin in humans. To answer this question, Al Rifai et al. used a range of experimental techniques to compare the structure and activity of osteocalcin in mice and humans.

The experiments showed that mouse osteocalcin has a group of sugars attached to its protein structure, which prevent the hormone from being degraded by an enzyme in the blood. Human osteocalcin has a slightly different protein sequence and is therefore unable to bind to this sugar group. As a result, the osteocalcin molecules in humans are less stable and cannot last as long in the blood. Al Rifai et al. showed that when human osteocalcin was modified so the sugar group could attach, the hormone was able to stick around for much longer and reach higher levels when added to blood in the laboratory.

These findings show how osteocalcin differs between human and mice. Understanding this difference is important as the effects of osteocalcin mean this hormone can be used to treat diabetes and brain disorders. Furthermore, the results reveal how the stability of osteocalcin could be improved in humans, which could potentially enhance its therapeutic effect.

Global view of human protein glycosylation pathways and functions

Glycosylation is the most abundant and diverse form of post-translational modification of proteins that is common to all eukaryotic cells. Enzymatic glycosylation of proteins involves a complex metabolic network and different types of glycosylation pathways that orchestrate enormous amplification of the proteome in producing diversity of proteoforms and its biological functions. The tremendous structural diversity of glycans attached to proteins poses analytical challenges that limit exploration of specific functions of glycosylation. Major advances in quantitative transcriptomics, proteomics and nuclease-based gene editing are now opening new global ways to explore protein glycosylation through analysing and targeting enzymes involved in glycosylation processes. In silico models predicting cellular glycosylation capacities and glycosylation outcomes are emerging, and refined maps of the glycosylation pathways facilitate genetic approaches to address functions of the vast glycoproteome. These approaches apply commonly available cell biology tools, and we predict that use of (single-cell) transcriptomics, genetic screens, genetic engineering of cellular glycosylation capacities and custom design of glycoprotein therapeutics are advancements that will ignite wider integration of glycosylation in general cell biology.