In the early 1980s, while using purified glycosyltransferases to probe glycan structures on surfaces of living cells in the murine immune system, we discovered a novel form of serine/threonine ...protein glycosylation (O-linked β-GlcNAc; O-GlcNAc) that occurs on thousands of proteins within the nucleus, cytoplasm, and mitochondria. Prior to this discovery, it was dogma that protein glycosylation was restricted to the luminal compartments of the secretory pathway and on extracellular domains of membrane and secretory proteins. Work in the last 3 decades from several laboratories has shown that O-GlcNAc cycling serves as a nutrient sensor to regulate signaling, transcription, mitochondrial activity, and cytoskeletal functions. O-GlcNAc also has extensive cross-talk with phosphorylation, not only at the same or proximal sites on polypeptides, but also by regulating each other’s enzymes that catalyze cycling of the modifications. O-GlcNAc is generally not elongated or modified. It cycles on and off polypeptides in a time scale similar to phosphorylation, and both the enzyme that adds O-GlcNAc, the O-GlcNAc transferase (OGT), and the enzyme that removes O-GlcNAc, O-GlcNAcase (OGA), are highly conserved from C. elegans to humans. Both O-GlcNAc cycling enzymes are essential in mammals and plants. Due to O-GlcNAc’s fundamental roles as a nutrient and stress sensor, it plays an important role in the etiologies of chronic diseases of aging, including diabetes, cancer, and neurodegenerative disease. This review will present an overview of our current understanding of O-GlcNAc’s regulation, functions, and roles in chronic diseases of aging.
The nutrient sensor, O-linked N-acetylglucosamine (O-GlcNAc), cycles on and off nuclear and cytosolic proteins to regulate many cellular processes, including transcription and signaling. Dysregulated ...O-GlcNAcylation and its interplay with phosphorylation contribute to the etiology of diabetes, cancer, and neurodegeneration. Herein, we review recent findings about O-GlcNAc’s regulation of cell physiology.
The nutrient sensor, O-linked N-acetylglucosamine (O-GlcNAc), cycles on and off nuclear and cytosolic proteins to regulate many cellular processes, including transcription and signaling. Dysregulated O-GlcNAcylation and its interplay with phosphorylation contribute to the etiology of diabetes, cancer, and neurodegeneration. Hardivillé and Hart review recent findings about O-GlcNAc’s regulation of cell physiology.
Protein O-linked β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation) is a unique monosaccharide modification discovered in the early 1980s. With the technological advances in the past ...several decades, great progress has been made to reveal the biochemistry of O-GlcNAcylation, the substrates of O-GlcNAcylation, and the functional importance of protein O-GlcNAcylation. As a nutrient sensor, protein O-GlcNAcylation plays important roles in almost all biochemical processes examined. Although the functional importance of O-GlcNAcylation of proteins has been extensively reviewed previously, the chemical and biochemical aspects have not been fully addressed. In this review, by critically evaluating key publications in the past 35 years, we aim to provide a comprehensive understanding of this important post-translational modification (PTM) from analytical and biochemical perspectives. Specifically, we will cover (1) multiple analytical advances in the characterization of O-GlcNAc cycling components (i.e., the substrate donor UDP-GlcNAc, the two key enzymes O-GlcNAc transferase and O-GlcNAcase, and O-GlcNAc substrate proteins), (2) the biochemical characterization of the enzymes with a variety of chemical tools, and (3) exploration of O-GlcNAc cycling and its modulating chemicals as potential biomarkers and therapeutic drugs for diseases. Last but not least, we will discuss the challenges and possible solutions for basic and translational research of protein O-GlcNAcylation in the future.
O-linked β-D-N-acetylglucosamine (O-GlcNAc) is an abundant post-translational modification (PTM) that modifies the serine or threonine residues of thousands of proteins in the nucleus, cytoplasm and ...mitochondria. Being a major “nutrient sensor” in cells, the O-GlcNAc pathway is sensitive to cellular metabolic states. Extensive crosstalk is observed between O-GlcNAcylation and protein phosphorylation. O-GlcNAc regulates protein functions at multiple levels, including enzymatic activity, transcriptional activity, subcellular localization, intermolecular interactions and degradation. Abnormal O-GlcNAcylation is associated with many human diseases including cancer, diabetes and neurodegenerative diseases. Though research on O-GlcNAc is still in its infantry, accumulating evidence suggest O-GlcNAcylation to be a promising therapeutic target. In this review, we briefly discuss the basic features of this PTM, the O-GlcNAc signaling pathway, its regulatory functions on different proteins, and its involvement in human diseases. We hope this review will provide insights to researchers who study human disease, as well as researchers who are interested in the fundamental roles of O-GlcNAcylation in all cells.
O-GlcNAcylation is the addition of β-D-N-acetylglucosamine to serine or threonine residues of nuclear and cytoplasmic proteins. O-linked N-acetylglucosamine (O-GlcNAc) was not discovered until the ...early 1980s and still remains difficult to detect and quantify. Nonetheless, O-GlcNAc is highly abundant and cycles on proteins with a timescale similar to protein phosphorylation. O-GlcNAc occurs in organisms ranging from some bacteria to protozoans and metazoans, including plants and nematodes up the evolutionary tree to man. O-GlcNAcylation is mostly on nuclear proteins, but it occurs in all intracellular compartments, including mitochondria. Recent glycomic analyses have shown that O-GlcNAcylation has surprisingly extensive cross talk with phosphorylation, where it serves as a nutrient/stress sensor to modulate signaling, transcription, and cytoskeletal functions. Abnormal amounts of O-GlcNAcylation underlie the etiology of insulin resistance and glucose toxicity in diabetes, and this type of modification plays a direct role in neurodegenerative disease. Many oncogenic proteins and tumor suppressor proteins are also regulated by O-GlcNAcylation. Current data justify extensive efforts toward a better understanding of this invisible, yet abundant, modification. As tools for the study of O-GlcNAc become more facile and available, exponential growth in this area of research will eventually take place.
High-throughput computational materials design is an emerging area of materials science. By combining advanced thermodynamic and electronic-structure methods with intelligent data mining and database ...construction, and exploiting the power of current supercomputer architectures, scientists generate, manage and analyse enormous data repositories for the discovery of novel materials. In this Review we provide a current snapshot of this rapidly evolving field, and highlight the challenges and opportunities that lie ahead.
Dynamic posttranslational modification of serine and threonine residues of nucleocytoplasmic proteins by β-N-acetylglucosamine (O-GlcNAc) is a regulator of cellular processes such as transcription, ...signaling, and protein-protein interactions. Like phosphorylation, O-GlcNAc cycles in response to a wide variety of stimuli. Although cycling of O-GlcNAc is catalyzed by only two highly conserved enzymes, O-GlcNAc transferase (OGT), which adds the sugar, and β-N-acetylglucosaminidase (O-GlcNAcase), which hydrolyzes it, the targeting of these enzymes is highly specific and is controlled by myriad interacting subunits. Here, we demonstrate by multiple specific immunological and enzymatic approaches that histones, the proteins that package DNA within the nucleus, are O-GlcNAcylated in vivo. Histones also are substrates for OGT in vitro. We identify O-GlcNAc sites on histones H2A, H2B, and H4 using mass spectrometry. Finally, we show that histone O-GlcNAcylation changes during mitosis and with heat shock. Taken together, these data show that O-GlcNAc cycles dynamically on histones and can be considered part of the histone code.
Elevated mitochondrial O -GlcNAcylation caused by hyperglycemia, as occurs in diabetes, significantly contributes to mitochondrial dysfunction and to diabetic cardiomyopathy. However, little is known ...about the enzymology of mitochondrial O -GlcNAcylation. Herein, we investigated the enzymes responsible for cycling O -GlcNAc on mitochondrial proteins and studied the mitochondrial transport of UDP-GlcNAc. Analyses of purified rat heart mitochondria from normal and streptozocin-treated diabetic rats show increased mitochondrial O -GlcNAc transferase (OGT) and a concomitant decrease in the mito-specific O-GlcNAcase (OGA). Strikingly, OGT is mislocalized in cardiac mitochondria from diabetic rats. Interaction of OGT and complex IV observed in normal rat heart mitochondria is visibly reduced in diabetic samples, where OGT is mislocalized to the matrix. Live cell OGA activity assays establish the presence of O-GlcNAcase within the mitochondria. Furthermore, we establish that the inner mitochondrial membrane transporter, pyrimidine nucleotide carrier, transports UDP-GlcNAc from the cytosol to the inside of the mitochondria. Knockdown of this transporter substantially lowers mitochondrial O -GlcNAcylation. Inhibition of OGT or OGA activity within neonatal rat cardiomyocytes significantly affects energy production, mitochondrial membrane potential, and mitochondrial oxygen consumption. These data suggest that cardiac mitochondria not only have robust O -GlcNAc cycling, but also that dysregulation of O -GlcNAcylation likely plays a key role in mitochondrial dysfunction associated with diabetes.
Significance Mitochondrial dysfunction contributes significantly to glucose toxicity in diabetes. Increased O -GlcNAcylation is emerging as a major molecular cause of glucose toxicity via many mechanisms. The studies herein provide a direct molecular link between hyperglycemia and mitochondrial dysfunction. We show that mitochondrial O -GlcNAc transferase (OGT) and O-GlcNAcase (OGA) expression levels and localizations are strikingly different between normal and diabetic rat hearts. We also discover how UDP-GlcNAc enters the mitochondrial space. Finally our data demonstrate that OGT and OGA play significant roles in ATP production, mitochondrial membrane potential, and oxygen consumption. These studies are of general interest not only with respect to nutrient regulation of mitochondrial function, but also are important to elucidate mechanisms of diabetic complications.
The dynamic cycling of N-acetylglucosamine (termed O-GlcNAcylation) on serine or threonine residues of nuclear or cytoplasmic proteins serves as a nutrient sensor, both independently and also via its ...interplay with other post-translational modifications, to regulate signaling, transcription, and cellular physiology. Emerging evidence suggests that dysregulation of this ubiquitous post-translational modification contributes to the etiology of some the most important human chronic diseases.
O-linked β-D-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation) onto serine and threonine residues of proteins is an important post-translational modification (PTM), which is involved in ...many crucial biological processes including transcription, translation, proteasomal degradation, and signal transduction. Aberrant protein O-GlcNAcylation is directly linked to the pathological progression of chronic diseases including diabetes, cancer, and neurodegenerative disorders. Identification, site mapping, and quantification of O-GlcNAc proteins are a prerequisite to decipher their functions. In this review, we mainly focus on technological developments regarding O-GlcNAc protein profiling. Specifically, on one hand, we show how these techniques are being used for the comprehensive characterization of certain targeted proteins in which biologists are most interested. On the other hand, we present several newly developed approaches for O-GlcNAcomic profiling as well as how they provide us with a systems perspective to crosstalk amongst different PTMs and complicated biological events. Promising technical trends are also highlighted to evoke more efforts by diverse laboratories, which would further expand our understanding of the physiological and pathological roles of protein O-GlcNAcylation in chronic diseases.
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