Detection and identification ofO-GlcNAcylated proteins by proteomic approaches

RNAPII Degradation Factor Def1 Is Required for Development, Stress Response, and Full Virulence of Magnaporthe oryzae

The RNA polymerase II degradation factor Degradation Factor 1 (Def1) is important for DNA damage repair and plays various roles in eukaryotes; however, the biological role in plant pathogenic fungi is still unknown. In this study, we investigated the role of Def1 during the development and infection of the rice blast fungus Magnaporthe oryzae. The deletion mutant of Def1 displayed slower mycelial growth, less conidial production, and abnormal conidial morphology. The appressoria of Δdef1 was impaired in the penetration into host cells, mainly due to blocking in the utilization of conidial storages, such as glycogen and lipid droplets. The invasive growth of the Δdef1 mutant was also retarded and accompanied with the accumulation of reactive oxygen species (ROS) inside the host cells. Furthermore, compared with the wild type, Δdef1 was more sensitive to multiple stresses, such as oxidative stress, high osmotic pressure, and alkaline/acidic pH. Interestingly, we found that Def1 was modified by O-GlcNAcylation at Ser232, which was required for the stability of Def1 and its function in pathogenicity. Taken together, the O-GlcNAc modified Def1 is required for hyphae growth, conidiation, pathogenicity, and stress response in M. oryzae. This study reveals a novel regulatory mechanism of O-GlcNAc-mediated Def1 in plant pathogenic fungi.

Elucidating the Implications of Norovirus N- and O-Glycosylation, O-GlcNAcylation, and Phosphorylation

Norovirus is the most common cause of foodborne gastroenteritis, affecting millions of people worldwide annually. Among the ten genotypes (GI-GX) of norovirus, only GI, GII, GIV, GVIII, and GIX infect humans. Some genotypes reportedly exhibit post-translational modifications (PTMs), including N- and O-glycosylation, O-GlcNAcylation, and phosphorylation, in their viral antigens. PTMs have been linked to increased viral genome replication, viral particle release, and virulence. Owing to breakthroughs in mass spectrometry (MS) technologies, more PTMs have been discovered in recent years and have contributed significantly to preventing and treating infectious diseases. However, the mechanisms by which PTMs act on noroviruses remain poorly understood. In this section, we outline the current knowledge of the three common types of PTM and investigate their impact on norovirus pathogenesis. Moreover, we summarize the strategies and techniques for the identification of PTMs.

Posttranslational modifications in diabetes: Mechanisms and functions

As one of the most widespread chronic diseases, diabetes and its accompanying complications affect approximately one tenth of individuals worldwide and represent a growing cause of morbidity and mortality. Accumulating evidence has proven that the process of diabetes is complex and interactive, involving various cellular responses and signaling cascades by posttranslational modifications (PTMs). Therefore, understanding the mechanisms and functions of PTMs in regulatory networks has fundamental importance for understanding the prediction, onset, diagnosis, progression, and treatment of diabetes. In this review, we offer a holistic summary and illustration of the crosstalk between PTMs and diabetes, including both types 1 and 2. Meanwhile, we discuss the potential use of PTMs in diabetes treatment and provide a prospective direction for deeply understanding the metabolic diseases.

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.

Evidence for nutrient-dependent regulation of the COPII coat by O-GlcNAcylation

O-linked β-N-acetylglucosamine (O-GlcNAc) is a dynamic form of intracellular glycosylation common in animals, plants and other organisms. O-GlcNAcylation is essential in mammalian cells and is dysregulated in myriad human diseases, such as cancer, neurodegeneration and metabolic syndrome. Despite this pathophysiological significance, key aspects of O-GlcNAc signaling remain incompletely understood, including its impact on fundamental cell biological processes. Here, we investigate the role of O-GlcNAcylation in the coat protein II complex (COPII), a system universally conserved in eukaryotes that mediates anterograde vesicle trafficking from the endoplasmic reticulum. We identify new O-GlcNAcylation sites on Sec24C, Sec24D and Sec31A, core components of the COPII system, and provide evidence for potential nutrient-sensitive pathway regulation through site-specific glycosylation. Our work suggests a new connection between metabolism and trafficking through the conduit of COPII protein O-GlcNAcylation.

Chemistry-Assisted Proteomic Profiling of O-GlcNAcylation

The modification on proteins with O-linked N-acetyl-β-D-glucosamine (O-GlcNAcylation) is essential for normal cell physiology. Dysregulation of O-GlcNAcylation leads to many human diseases, such as cancer, diabetes and neurodegenerative diseases. Recently, the functional role of O-GlcNAcylation in different physiological states has been elucidated due to the booming detection technologies. Chemical approaches for the enrichment of O-GlcNAcylated proteins combined with mass spectrometry-based proteomics enable the profiling of protein O-GlcNAcylation in a system-wide level. In this review, we summarize recent progresses on the enrichment and proteomic profiling of protein O-GlcNAcylation.

O-GlcNAcylation Prediction: An Unattained Objective

BACKGROUND

O-GlcNAcylation is an essential post-translational modification (PTM) in mammalian cells. It consists in the addition of a N-acetylglucosamine (GlcNAc) residue onto serines or threonines by an O-GlcNAc transferase (OGT). Inhibition of OGT is lethal, and misregulation of this PTM can lead to diverse pathologies including diabetes, Alzheimer's disease and cancers. Knowing the location of O-GlcNAcylation sites and the ability to accurately predict them is therefore of prime importance to a better understanding of this process and its related pathologies.

PURPOSE

Here, we present an evaluation of the current predictors of O-GlcNAcylation sites based on a newly built dataset and an investigation to improve predictions.

METHODS

Several datasets of experimentally proven O-GlcNAcylated sites were combined, and the resulting meta-dataset was used to evaluate three prediction tools. We further defined a set of new features following the analysis of the primary to tertiary structures of experimentally proven O-GlcNAcylated sites in order to improve predictions by the use of different types of machine learning techniques.

RESULTS

Our results show the failure of currently available algorithms to predict O-GlcNAcylated sites with a precision exceeding 9%. Our efforts to improve the precision with new features using machine learning techniques do succeed for equal proportions of O-GlcNAcylated and non-O-GlcNAcylated sites but fail like the other tools for real-life proportions where ~1.4% of S/T are O-GlcNAcylated.

CONCLUSION

Present-day algorithms for O-GlcNAcylation prediction narrowly outperform random prediction. The inclusion of additional features, in combination with machine learning algorithms, does not enhance these predictions, emphasizing a pressing need for further development. We hypothesize that the improvement of prediction algorithms requires characterization of OGT's partners.

A lable-free SPR biosensor based on one peptide sequence with three recognition sites for O-GlcNAc transferase detection

Abnormal O-linked N-acetylglucosamine (O-GlcNAc) concentrations have been associated with many diseases, but the lack of accurate detection method limited O-GlcNAc to be used as a biomarker in clinical diagnosis. Then O-GlcNAc transferase (OGT) has drawn researchers' attention as it closed related to the level of O-GlcNAc and be considered to be a promising new target for diseases diagnosis. Nevertheless, the existing OGT detection methods are either need labeling or the sensitity can not meet the needs of clinic testing. Herein, a label-free and sensitive SPR biosensor was developed for accurate detection of OGT based on a multi-functional peptide. The designed peptide contains three recognition sites, one is the cleavage site of protease K, one is the O-GlcNAcylated site by OGT, and another is six histidine which be used as the signal report probe to recognize Ni²⁺. The immobilized peptide would be cleavaged by proteinase K, then the His-tag residue part will leave the surface of Au film, resulting less His-tag could bind to Ni²⁺ and a small SPR signal would be record. If the peptide is O-GlcNAcylated by OGT, the cleaving reaction would be limited due to the adjacent site of O-GlcNAcylation. Then more His-tag can be left on the Au film and a bigger SPR signal could be record, this signal is associated with the concentration of OGT. Utilizing the change of the peptide configuration as a signal report probe for OGT detection not only avoids labeling of peptide, but also makes the method more sensitive. The determination linear range of OGT is from 2.00 × 10^-13 to 5.00 × 10^-8 M with a detection limit of 1.19 × 10^-13 M, and the separation of two enzyme reactions ensured the high selectivity of the method. Finally, the sensing system was successfully used for OGT detection in blood samples with satisfied recovery. In summary, the label-free SPR platform for accurate detection of OGT in real samples is helpful to promote OGT serve as a biomarker for early clinical diagnosis of O-GlcNAc related diseases.

Precision Mapping of O-Linked N-Acetylglucosamine Sites in Proteins Using Ultraviolet Photodissociation Mass Spectrometry

Despite its central importance as a regulator of cellular physiology, identification and precise mapping of O-linked N-acetylglucosamine (O-GlcNAc) post-translational modification (PTM) sites in proteins by mass spectrometry (MS) remains a considerable technical challenge. This is due in part to cleavage of the glycosidic bond occurring prior to the peptide backbone during collisionally activated dissociation (CAD), which leads to generation of characteristic oxocarbenium ions and impairs glycosite localization. Herein, we leverage CAD-induced oxocarbenium ion generation to trigger ultraviolet photodissociation (UVPD), an alternate high-energy deposition method that offers extensive fragmentation of peptides while leaving the glycosite intact. Upon activation using UV laser pulses, efficient photodissociation of glycopeptides is achieved with production of multiple sequence ions that enable robust and precise localization of O-GlcNAc sites. Application of this method to tryptic peptides originating from O-GlcNAcylated proteins TAB1 and Polyhomeotic confirmed previously reported O-GlcNAc sites in TAB1 (S395 and S396) and uncovered new sites within both proteins. We expect this strategy will complement existing MS/MS methods and be broadly useful for mapping O-GlcNAcylated residues of both proteins and proteomes.

Improved Alignment and Quantification of Protein Signals in Two-Dimensional Western Blotting

Western blotting is widely used for protein identification and quantification in research applications, but different protein species, resulting from alternative splicing and post-translational modifications, can often only be detected individually by two-dimensional gel electrophoresis and immunodetection by Western blotting (2D-WB). The additional separation by isoelectric focusing enables the detection of different protein species with the same specific antibody. Reliable assignment of signals from antibody-based detection to the total protein spot pattern of the original gel image is a challenge in 2D-WB, often resulting in ambiguous results. We therefore propose a reliable strategy for assignment of antibody signals from 2D-WB to the total protein spot pattern, using an imaging workflow in combination with a straightforward and easily reproducible image alignment strategy. The strategy employs vector-based alignment of protein spots and image contours in a stepwise manner. Our workflow is compatible with various protein visualization techniques, including prelabeling of proteins and poststaining of gels and membranes, as well as with chemiluminescent and fluorescent detection of bound antibody. Here, we provide a detailed description of potential applications and benefits of our workflow. We use experimental test settings with gold-standard stressors in combination with multiple staining and detection methods, as well as spike-in recombinant proteins. Our results demonstrate reliable attribution of signals to very similar heat shock proteins, phosphorylation patterns, and global analysis of proteins modified with O-linked N-acetylglucosamine (O-GlcNAc).

Structures and functions of invertebrate glycosylation

Glycosylation refers to the covalent attachment of sugar residues to a protein or lipid, and the biological importance of this modification has been widely recognized. While glycosylation in mammals is being extensively investigated, lower level animals such as invertebrates have not been adequately interrogated for their glycosylation. The rich diversity of invertebrate species, the increased database of sequenced invertebrate genomes and the time and cost efficiency of raising and experimenting on these species have enabled a handful of the species to become excellent model organisms, which have been successfully used as tools for probing various biologically interesting problems. Investigation on invertebrate glycosylation, especially on model organisms, not only expands the structural and functional knowledgebase, but also can facilitate deeper understanding on the biological functions of glycosylation in higher organisms. Here, we reviewed the research advances in invertebrate glycosylation, including N- and O-glycosylation, glycosphingolipids and glycosaminoglycans. The aspects of glycan biosynthesis, structures and functions are discussed, with a focus on the model organisms Drosophila and Caenorhabditis. Analytical strategies for the glycans and glycoconjugates are also summarized.

Acutely elevated O-GlcNAcylation suppresses hippocampal activity by modulating both intrinsic and synaptic excitability factors

Post-translational modification (PTM) plays a critical role in increasing proteome complexity and diversifying protein functions. O-GlcNAc modification is a reversible, dynamic and highly abundant PTM catalyzed by a single pair of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), regardless of substrates. The two enzymes are particularly enriched in the brain, and recent proteomic studies identified that a large number of neuron-specific proteins undergo O-GlcNAc modification. In addition, pathological conditions with aberrant O-GlcNAcylation such as diabetes and obesity are associated with the higher risk of cognitive decline and memory impairment. However, despite its prevalence in the brain, functional significance of O-GlcNAcylation in regulating neuronal properties remains unclear at the molecular level. Here, we report that an acute increase in O-GlcNAcylation induced by pharmacological inhibition of OGA significantly reduces the intrinsic excitability of hippocampal CA1 neurons through the cooperative modulation of multiple voltage-gated ion channels. Moreover, elevated O-GlcNAcylation also suppresses excitatory synaptic transmission at Schaffer collateral-CA1 synapses through the removal of GluA2-containing AMPA receptors from postsynaptic densities. Collectively, our findings demonstrate that a change in O-GlcNAcylation levels dynamically regulates hippocampal activity at both intrinsic and synaptic levels, providing a mechanistic link between dysregulated O-GlcNAcylation and hippocampal dysfunction.

Identification of O-Glcnacylated Proteins in Trypanosoma cruzi

Originally an anthropozoonosis in the Americas, Chagas disease has spread from its previous borders through migration. It is caused by the protozoan Trypanosoma cruzi. Differences in disease severity have been attributed to a natural pleomorphism in T. cruzi. Several post-translational modifications (PTMs) have been studied in T. cruzi, but to date no work has focused on O-GlcNAcylation, a highly conserved monosaccharide-PTM of serine and threonine residues mainly found in nucleus, cytoplasm, and mitochondrion proteins. O-GlcNAcylation is thought to regulate protein function analogously to protein phosphorylation; indeed, crosstalk between both PTMs allows the cell to regulate its functions in response to nutrient levels and stress. Herein, we demonstrate O-GlcNAcylation in T. cruzi epimastigotes by three methods: by using specific antibodies against the modification in lysates and whole parasites, by click chemistry labeling, and by proteomics. In total, 1,271 putative O-GlcNAcylated proteins and six modification sequences were identified by mass spectrometry (data available via ProteomeXchange, ID PXD010285). Most of these proteins have structural and metabolic functions that are essential for parasite survival and evolution. Furthermore, O-GlcNAcylation pattern variations were observed by antibody detection under glucose deprivation and heat stress conditions, supporting their possible role in the adaptive response. Given the numerous biological processes in which O-GlcNAcylated proteins participate, its identification in T. cruzi proteins opens a new research field in the biology of Trypanosomatids, improve our understanding of infection processes and may allow us to identify new therapeutic targets.

The Many Ways by Which O-GlcNAcylation May Orchestrate the Diversity of Complex Glycosylations

Unlike complex glycosylations, O-GlcNAcylation consists of the addition of a single N-acetylglucosamine unit to serine and threonine residues of target proteins, and is confined within the nucleocytoplasmic and mitochondrial compartments. Nevertheless, a number of clues tend to show that O-GlcNAcylation is a pivotal regulatory element of its complex counterparts. In this perspective, we gather the evidence reported to date regarding this connection. We propose different levels of regulation that encompass the competition for the nucleotide sugar UDP-GlcNAc, and that control the wide class of glycosylation enzymes via their expression, catalytic activity, and trafficking. We sought to better envision that nutrient fluxes control the elaboration of glycans, not only at the level of their structure composition, but also through sweet regulating actors.

Surface plasmon resonance biosensor for the accurate and sensitive quantification of O-GlcNAc based on cleavage by β-D-N-acetylglucosaminidase

Abnormal O-linked-N-acetylglucosamine (O-GlcNAc) concentrations have been associated with a variety of diseases (e.g., cancer, Alzheimer's disease, cardiovascular disease, etc.). However, O-GlcNAc detection is complicated, time-consuming and has poor specificity, therefore, the accurate detection of O-GlcNAc is difficult. In this study, an accurate and sensitive surface plasmon resonance (SPR) biosensor for O-GlcNAc detection that is based on β-D-N-acetylglucosaminidase (OGA) and Au nanoparticles (AuNPs) was developed. In this strategy, AuNPs were used to amplify the SPR signal and improve the biosensor's sensitivity; OGA was used to cleave O-GlcNAc from O-GlcNAcylated biomolecules. The interaction between AuNPs labeled wheat germ agglutinin (AuNPs/WGA) and O-GlcNAcylated biomolecules on a modified Au film treated with and without OGA was recorded by SPR. The change of the SPR signal moves linearly with the amount of O-GlcNAc on the Au film and thus could be used for the detection of O-GlcNAc. By recording the difference of the SPR signals, this method can avoid disturbances from other sugars and nonspecific adsorption of AuNPs and thus enable the accurate detection of O-GlcNAc. The accurate detection range of O-GlcNAc was 4.65 × 10^-12 to 4.65 × 10^-7 M which was obtained by quantifying the amount of a standard O-GlcNAcylated peptide (O-GlcNAc-CREB), and the detection limit is 4.65 × 10^-13 M. More importantly, the strategy was successfully used to detect O-GlcNAc in a real α-crystallin protein, cancer cell lysates and blood samples with satisfactory results. The study's results imply that this accurate and sensitive method has the potential to be applied in the early clinical diagnosis of O-GlcNAc-related diseases.

Apart From Rhoptries, Identification of Toxoplasma gondii's O-GlcNAcylated Proteins Reinforces the Universality of the O-GlcNAcome

O-linked β-N-acetylglucosaminylation or O-GlcNAcylation is a widespread post-translational modification that belongs to the large and heterogeneous group of glycosylations. The functions managed by O-GlcNAcylation are diverse and include regulation of transcription, replication, protein's fate, trafficking, and signaling. More and more evidences tend to show that deregulations in the homeostasis of O-GlcNAcylation are involved in the etiology of metabolic diseases, cancers and neuropathologies. O-GlcNAc transferase or OGT is the enzyme that transfers the N-acetylglucosamine residue onto target proteins confined within the cytosolic and nuclear compartments. A form of OGT was predicted for Toxoplasma and recently we were the first to show evidence of O-GlcNAcylation in the apicomplexans Toxoplasma gondii and Plasmodium falciparum. Numerous studies have explored the O-GlcNAcome in a wide variety of biological models but very few focus on protists. In the present work, we used enrichment on sWGA-beads and immunopurification to identify putative O-GlcNAcylated proteins in Toxoplasma gondii. Many of the proteins found to be O-GlcNAcylated were originally described in higher eukaryotes and participate in cell shape organization, response to stress, protein synthesis and metabolism. In a more original way, our proteomic analyses, confirmed by sWGA-enrichment and click-chemistry, revealed that rhoptries, proteins necessary for invasion, are glycosylated. Together, these data show that regardless of proteins strictly specific to organisms, O-GlcNAcylated proteins are rather similar among living beings.

Simple method for O-GlcNAc sensitive detection based on graphene quantum dots

Simple and sensitive method for O-GlcNAc detection in cell lysates based on graphene quantum dots combination; WGA was successfully developed.

Insights into the role of maladaptive hexosamine biosynthesis and O-GlcNAcylation in development of diabetic cardiac complications

Diabetes mellitus significantly increases the risk of heart failure, independent of coronary artery disease. The mechanisms implicated in the development of diabetic heart disease, commonly termed diabetic cardiomyopathy, are complex, but much of the impact of diabetes on the heart can be attributed to impaired glucose handling. It has been shown that the maladaptive nutrient-sensing hexosamine biosynthesis pathway (HBP) contributes to diabetic complications in many non-cardiac tissues. Glucose metabolism by the HBP leads to enzymatically-regulated, O-linked attachment of a sugar moiety molecule, β-N-acetylglucosamine (O-GlcNAc), to proteins, affecting their biological activity (similar to phosphorylation). In normal physiology, transient activation of HBP/O-GlcNAc mechanisms is an adaptive, protective means to enhance cell survival; interventions that acutely suppress this pathway decrease tolerance to stress. Conversely, chronic dysregulation of HBP/O-GlcNAc mechanisms has been shown to be detrimental in certain pathological settings, including diabetes and cancer. Most of our understanding of the impact of sustained maladaptive HBP and O-GlcNAc protein modifications has been derived from adipose tissue, skeletal muscle and other non-cardiac tissues, as a contributing mechanism to insulin resistance and progression of diabetic complications. However, the long-term consequences of persistent activation of cardiac HBP and O-GlcNAc are not well-understood; therefore, the goal of this timely review is to highlight current understanding of the role of the HBP pathway in development of diabetic cardiomyopathy.

O-GlcNAcylation, enemy or ally during cardiac hypertrophy development?

O-linked attachment of the monosaccharide β-N-acetyl-glucosamine (O-GlcNAcylation) is a post-translational modification occurring on serine and threonine residues, which is evolving as an important mechanism for the regulation of various cellular processes. The present review will, first, provide a general background on the molecular regulation of protein O-GlcNAcylation and will summarize the role of this post-translational modification in various acute cardiac pathologies including ischemia-reperfusion. Then, we will focus on research studies examining protein O-GlcNAcylation in the context of cardiac hypertrophy. A particular emphasis will be laid on the convergent but also divergent actions of O-GlcNAcylation according to the type of hypertrophy investigated, including physiological, pressure overload-induced and diabetes-linked cardiac hypertrophy. In an attempt to distinguish whether O-GlcNAcylation is detrimental or beneficial, this review will present the different O-GlcNAcylated targets involved in hypertrophy development. We will finally argue on potential interest to target O-GlcNAc processes to treat cardiac hypertrophy. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

Synthetic Receptors for the High-Affinity Recognition of O-GlcNAc Derivatives

The combination of a pyrenyl tetraamine with an isophthaloyl spacer has led to two new water-soluble carbohydrate receptors ("synthetic lectins"). Both systems show outstanding affinities for derivatives of N-acetylglucosamine (GlcNAc) in aqueous solution. One receptor binds the methyl glycoside GlcNAc-β-OMe with Ka ≈20,000 m(-1), whereas the other one binds an O-GlcNAcylated peptide with Ka ≈70,000 m(-1). These values substantially exceed those usually measured for GlcNAc-binding lectins. Slow exchange on the NMR timescale enabled structural determinations for several complexes. As expected, the carbohydrate units are sandwiched between the pyrenes, with the alkoxy and NHAc groups emerging at the sides. The high affinity of the GlcNAcyl-peptide complex can be explained by extra-cavity interactions, raising the possibility of a family of complementary receptors for O-GlcNAc in different contexts.

Senescence-Associated Changes in Proteome and O-GlcNAcylation Pattern in Human Peritoneal Mesothelial Cells

INTRODUCTION

Senescence of peritoneal mesothelial cells represents a biological program defined by arrested cell growth and altered cell secretory phenotype with potential impact in peritoneal dialysis. This study aims to characterize cellular senescence at the level of global protein expression profiles and modification of proteins with O-linked N-acetylglucosamine (O-GlcNAcylation).

METHODS

A comparative proteomics analysis between young and senescent human peritoneal mesothelial cells (HPMC) was performed using two-dimensional gel electrophoresis. O-GlcNAc status was assessed by Western blot under normal conditions and after modulation with 6-diazo-5-oxo-L-norleucine (DON) to decrease O-GlcNAcylation or O-(2-acetamido-2-deoxy-D-glucopyranosylidene) amino N-phenyl carbamate (PUGNAc) to increase O-GlcNAcylation.

RESULTS

Comparison of protein pattern of senescent and young HPMC revealed 29 differentially abundant protein spots, 11 of which were identified to be actin (cytoplasmic 1 and 2), cytokeratin-7, cofilin-2, transgelin-2, Hsp60, Hsc70, proteasome β-subunits (type-2 and type-3), nucleoside diphosphate kinase A, and cytosolic 5'(3')-deoxyribonucleotidase. Although the global level of O-GlcNAcylation was comparable, senescent cells were not sensitive to modulation by PUGNAc.

DISCUSSION

This study identified changes of the proteome and altered dynamics of O-GlcNAc regulation in senescent mesothelial cells. Whereas changes in cytoskeleton-associated proteins likely reflect altered cell morphology, changes in chaperoning and housekeeping proteins may have functional impact on cellular stress response in peritoneal dialysis.

Post-translational modifications of the cardiac proteome in diabetes and heart failure

Cardiovascular complications are the leading cause of death in diabetic patients. Decades of research has focused on altered gene expression, altered cellular signaling, and altered metabolism. This work has led to better understanding of disease progression and treatments aimed at reversing or stopping this deadly process. However, one of the pieces needed to complete the puzzle and bridge the gap between altered gene expression and changes in signaling/metabolism is the proteome and its host of modifications. Defining the mechanisms of regulation includes examining protein levels, localization, and activity of the functional component of cellular machinery. Excess or misutilization of nutrients in obesity and diabetes may lead to PTMs contributing to cardiovascular disease progression. PTMs link regulation of metabolic changes in the healthy and diseased heart with regulation of gene expression itself (e.g. epigenetics), protein enzymatic activity (e.g. mitochondrial oxidative capacity), and function (e.g. contractile machinery). Although a number of PTMs are involved in each of these pathways, we will highlight the role of the serine and threonine O‐linked addition of β‐N‐acetyl‐glucosamine or O‐GlcNAcylation. This nexus of nutrient supply, utilization, and storage allows for the modification and translation of mitochondrial function to many other aspects of the cell.

The Utilities of Chemical Reactions and Molecular Tools for O-GlcNAc Proteomic Studies

The post-translational modification of nuclear and cytoplasmic proteins with O-linked β-N-acetylglucosamine (O-GlcNAc) is involved in a wide variety of cellular processes and is associated with the pathological progression of chronic diseases. Considering its emerging biological significance, systematic identification, site mapping, and quantification of O-GlcNAc proteins are essential and have led to the development of several approaches for O-GlcNAc protein profiling. This minireview mainly focuses on the various useful chemical reactions and molecular tools with detailed reaction mechanisms widely adopted for O-GlcNAc protein/peptide enrichment and its quantification for comprehensive O-GlcNAc protein profiling.