O-GlcNAcylation: cellular physiology and therapeutic target for human diseases

O-linked-β-N-acetylglucosamine (O-GlcNAcylation) is a distinctive posttranslational protein modification involving the coordinated action of O-GlcNAc transferase and O-GlcNAcase, primarily targeting serine or threonine residues in various proteins. This modification impacts protein functionality, influencing stability, protein-protein interactions, and localization. Its interaction with other modifications such as phosphorylation and ubiquitination is becoming increasingly evident. Dysregulation of O-GlcNAcylation is associated with numerous human diseases, including diabetes, nervous system degeneration, and cancers. This review extensively explores the regulatory mechanisms of O-GlcNAcylation, its effects on cellular physiology, and its role in the pathogenesis of diseases. It examines the implications of aberrant O-GlcNAcylation in diabetes and tumorigenesis, highlighting novel insights into its potential role in cardiovascular diseases. The review also discusses the interplay of O-GlcNAcylation with other protein modifications and its impact on cell growth and metabolism. By synthesizing current research, this review elucidates the multifaceted roles of O-GlcNAcylation, providing a comprehensive reference for future studies. It underscores the potential of targeting the O-GlcNAcylation cycle in developing novel therapeutic strategies for various pathologies.

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.

Understanding the Function of Mammalian Sirtuins and Protein Lysine Acylation

Protein lysine acetylation is an important posttranslational modification that regulates numerous biological processes. Targeting lysine acetylation regulatory factors, such as acetyltransferases, deacetylases, and acetyl-lysine recognition domains, has been shown to have potential for treating human diseases, including cancer and neurological diseases. Over the past decade, many other acyl-lysine modifications, such as succinylation, crotonylation, and long-chain fatty acylation, have also been investigated and shown to have interesting biological functions. Here, we provide an overview of the functions of different acyl-lysine modifications in mammals. We focus on lysine acetylation as it is well characterized, and principles learned from acetylation are useful for understanding the functions of other lysine acylations. We pay special attention to the sirtuins, given that the study of sirtuins has provided a great deal of information about the functions of lysine acylation. We emphasize the regulation of sirtuins to illustrate that their regulation enables cells to respond to various signals and stresses.

Effects of protein posttranslational modifications on meat quality: A review

Meat quality plays an important role in the purchase decision of consumers, affecting producers and retailers. The formation mechanisms determining meat quality are intricate, as several endogenous and exogenous factors contribute during antemortem and postmortem periods. Abundant research has been performed on meat quality; however, unexpected variation in meat quality remains an issue in the meat industry. Protein posttranslational modifications (PTMs) regulate structures and functions of proteins in living tissues, and recent reports confirmed their importance in meat quality. The objective of this review was to provide a summary of the research on the effects of PTMs on meat quality. The effects of four common PTMs, namely, protein phosphorylation, acetylation, S-nitrosylation, and ubiquitination, on meat quality were discussed, with emphasis on the effects of protein phosphorylation on meat tenderness, color, and water holding capacity. The mechanisms and factors that may affect the function of protein phosphorylation are also discussed. The current research confirms that meat quality traits are regulated by multiple PTMs. Cross talk between different PTMs and interactions of PTMs with postmortem biochemical processes need to be explored to improve our understanding on factors affecting meat quality.

Posttranslational lysine 2-hydroxyisobutyrylation of human sperm tail proteins affects motility

STUDY QUESTION

Does lysine 2-hydroxyisobutyrylation, a newly identified protein posttranslational modification (PTM), occur in human sperm and affect human sperm function?

SUMMARY ANSWER

Lysine 2-hydroxyisobutyrylation mainly occurs in human sperm tail proteins, and excessive lysine 2-hydroxyisobutyrylation affects human sperm motility.

WHAT IS KNOWN ALREADY

PTM is regarded as an important pathway in regulating sperm function since mature sperm are almost transcriptionally silent. However, only phosphorylation was extensively studied in mature sperm to date. Lysine 2-hydroxyisobutyrylation, a newly characterised PTM, is broadly conserved in both eukaryotic and prokaryotic cells. Although histone lysine 2-hydroxyisobutyrylation has been shown to be associated with active gene expression in spermatogenic cells, the presence, regulatory elements and function of lysine 2-hydroxyisobutyrylation have not been characterised in mature sperm.

STUDY DESIGN, SIZE, DURATION

Sperm samples were obtained from normozoospermic men and asthenozoospermic men who visited the reproductive medical centre at Jiangxi Provincial Maternal and Child Health Hospital, Nanchang, Jiangxi, China, between May 2017 and November 2018. In total, 58 normozoospermic men and 65 asthenozoospermic men were recruited to participate in this study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Lysine 2-hydroxyisobutyrylation was examined using immunoblotting and immunofluorescence assays using a previously qualified pan anti-lysine 2-hydroxyisobutyrylation antibody. The immunofluorescence assay was imaged using super-resolution structured illumination microscopy. Sperm viability was examined by using the eosin staining method, and sperm motility parameters were assessed by computer-assisted sperm analysis. Sperm penetration ability was determined by evaluating the ability of the sperm to penetrate a 1% (w/v) methylcellulose solution. The level of intracellular adenosine triphosphate (ATP) was detected using a rapid bioluminescent ATP assay kit.

MAIN RESULTS AND THE ROLE OF CHANCE

Lysine 2-hydroxyisobutyrylation was present in several proteins (20-100 kDa) mainly located in the tail of human sperm. Sperm lysine 2-hydroxyisobutyrylation was derived from 2-hydroxyisobutyrate (2-Hib) and was regulated by acyltransferase P300 and nicotinamide adenine dinucleotide-dependent lysine deacylase sirtuins. Elevation of sperm lysine 2-hydroxyisobutyrylation by 2-Hib decreased total motility, progressive motility, penetration ability and ATP level of human sperm. Interestingly, the level of sperm lysine 2-hydroxyisobutyrylation was higher in asthenozoospermic men than that in normozoospermic men and was negatively correlated with the progressive motility of human sperm. Furthermore, high levels of lysine 2-hydroxyisobutyrylation in asthenozoospermic men accompanied decreased ATP levels.

LIMITATIONS, REASONS FOR CAUTION

Although the present study indicated the involvement of sperm lysine 2-hydroxyisobutyrylation in regulating human sperm motility, the underlying mechanism needs to be further illustrated.

WIDER IMPLICATIONS OF THE FINDINGS

The findings of this study provide insight into the novel role of lysine 2-hydroxyisobutyrylation in human sperm and suggest that abnormality of sperm lysine 2-hydroxyisobutyrylation may be one of the causes for asthenozoospermia.

STUDY FUNDING/COMPETING INTEREST(S)

National Natural Science Foundation of China (81771644 to T.L. and 81871207 to H.C.); Natural Science Foundation of Jiangxi province (20171ACB21006). The authors have no conflicts of interest to declare.

2-Hydroxyisobutyrylation on histone H4K8 is regulated by glucose homeostasis in Saccharomyces cerevisiae

New types of modifications of histones keep emerging. Recently, histone H4K8 2-hydroxyisobutyrylation (H4K8_hib) was identified as an evolutionarily conserved modification. However, how this modification is regulated within a cell is still elusive, and the enzymes adding and removing 2-hydroxyisobutyrylation have not been found. Here, we report that the amount of H4K8_hib fluctuates in response to the availability of carbon source in Saccharomyces cerevisiae and that low-glucose conditions lead to diminished modification. The removal of the 2-hydroxyisobutyryl group from H4K8 is mediated by the histone lysine deacetylase Rpd3p and Hos3p in vivo. In addition, eliminating modifications at this site by alanine substitution alters transcription in carbon transport/metabolism genes and results in a reduced chronological life span (CLS). Furthermore, consistent with the glucose-responsive H4K8_hib regulation, proteomic analysis revealed that a large set of proteins involved in glycolysis/gluconeogenesis are modified by lysine 2-hydroxyisobutyrylation. Cumulatively, these results established a functional and regulatory network among K_hib, glucose metabolism, and CLS.