表皮生长因子样重复序列糖基化对Notch信号通路的作用

Notch受体是一类存在于多细胞生物中进化上高度保守的跨膜蛋白受体,其介导的信号通路在组织器官的生长发育中起重要作用。糖基化修饰是一类重要的影响多信号通路的蛋白翻译后修饰。Notch受体胞外域的表皮生长因子样重复序列（EGF-R）存在多种糖基化修饰如O-葡聚糖、O-岩藻糖聚糖、O- N-乙酰氨基葡萄糖,这些糖基化修饰可以促进或抑制Notch信号通路。本文主要阐述表皮生长因子样重复序列（EGF-R）的主要糖基化以及对Notch信号通路的影响和其异常导致相关的疾病。     

Chromosomal histone modification patterns--from conservation to diversity

The organization of DNA into chromatin regulates expression and maintenance (replication, repair, recombination, segregation) of genetic information in a dynamic manner. The N-terminal tails of the nucleosomal core histones are subjected to post-translational modifications such as acetylation, methylation, phosphorylation, ubiquitination, glycosylation, ADP-ribosylation, carbonylation and sumoylation. These modifications, together with DNA methylation, control the folding of the nucleosomal array into higher order structures and mediate signalling for cellular processes. Although histones and their modifications are highly conserved, recent data show that chromosomal distribution of individual modifications (acetylation, methylation, phosphorylation) can differ along the cell cycle as well as among and between groups of eukaryotes. This implies the possibility of evolutionary divergence in reading the "histone code".     

Mummy encodes an UDP-N-acetylglucosamine-dipohosphorylase and is required during Drosophila dorsal closure and nervous system development

Throughout development cell-cell interactions are of pivotal importance. Cells bind to each other or share information via secreted signaling molecules. To a large degree, these processes are modulated by post-translational modifications of membrane proteins. Glycan-chains are frequently added to membrane proteins and assist their exact function at the cell surface. In addition, the glycosylation pathway is required to generate GPI-linkage in the endoplasmatic reticulum. Here, we describe the analysis of the cabrio/mummy gene, which encodes an UDP-N-acetylglucosamine diphosphorylase. This is a well-conserved and central enzyme in the glycosylation pathway. As expected from this central role in glycosylation, cabrio/mummy mutants show many phenotypic traits ranging from CNS fasciculation defects to defects in dorsal closure and eye development. These phenotypes correlate well with specific glycosylation and GPI-anchorage defects in mummy mutants.     

细菌中常见的蛋白翻译后修饰

蛋白质的翻译后修饰在生物体生命活动中发挥着重要作用,大部分蛋白质都会经历翻译后修饰。对这些修饰的了解和掌握非常重要,因为这些修饰可能会改变蛋白质的物理及化学性质,如折叠、构象、稳定性及活性,从而改变蛋白的功能。此外,修饰基团本身也可能具有某些功能。因此,分析研究蛋白质翻译后修饰具有重要意义。细菌中常见的翻译后修饰过程有糖基化、磷酸化和乙酰化,我们简要综述了这几种修饰过程。     

N-糖肽的规模化质谱解析方法进展

蛋白质糖基化修饰的鉴定是蛋白质翻译后修饰分析中最具挑战性的任务之一,近几年尤其受到关注.快速发展的质谱技术为规模化的蛋白质糖基化修饰研究提供了有效的手段.与其他基于质谱技术的翻译后修饰鉴定相比,糖基化鉴定的难点在于糖链是大分子而且存在微观不均一性,另外糖链本身可以在串联质谱中碎裂且与肽段的碎裂规律不同,导致蛋白质组学的质谱解析方法和软件难以完整地鉴定肽段序列和糖链结构.完整N-糖肽的鉴定是糖基化分析的热点内容之一,针对N-糖肽的鉴定,近年来,人们开发了多种多样的质谱解析方法,其中包括用N-糖酰胺酶切除糖链后鉴定N-糖基化位点的方法、基于电子转运裂解的糖肽肽段鉴定、基于高能碰撞裂解与电子转运裂解联用或碰撞诱导裂解与三级谱联用的完整N-糖肽鉴定等等.本文对这些质谱解析方法进行了整理和综述,简要指出了目前完整糖肽鉴定软件存在的一些不足,展望了未来的发展方向.     

Post-translational modifications mediated by reactive nitrogen species: Nitrosative stress responses or components of signal transduction pathways?

In animal cells, nitric oxide and NO-derived molecules have been shown to mediate post-translational modifications such as S-nitrosylation and protein tyrosine nitration which are associated with cell signalling and pathological processes, respectively. In plant cells, knowledge of the function of these post-translational modifications under physiological and stress conditions is still very rudimentary. In this addendum, we briefly examine how reactive nitrogen species (RNS) can exert important effects on proteins that could mediate signalling processes in plants.Key words: nitrosative stress, nitric oxide synthase, S-nitrosoglutathione, nitro-tyrosine, post-translational modifications, S-nitrosylation     

Importance of post-translational modifications for functionality of a chloroplast-localized carbonic anhydrase (CAH1) in Arabidopsis thaliana

Background

The Arabidopsis CAH1 alpha-type carbonic anhydrase is one of the few plant proteins known to be targeted to the chloroplast through the secretory pathway. CAH1 is post-translationally modified at several residues by the attachment of N-glycans, resulting in a mature protein harbouring complex-type glycans. The reason of why trafficking through this non-canonical pathway is beneficial for certain chloroplast resident proteins is not yet known. Therefore, to elucidate the significance of glycosylation in trafficking and the effect of glycosylation on the stability and function of the protein, epitope-labelled wild type and mutated versions of CAH1 were expressed in plant cells.

Methodology/Principal Findings

Transient expression of mutant CAH1 with disrupted glycosylation sites showed that the protein harbours four, or in certain cases five, N-glycans. While the wild type protein trafficked through the secretory pathway to the chloroplast, the non-glycosylated protein formed aggregates and associated with the ER chaperone BiP, indicating that glycosylation of CAH1 facilitates folding and ER-export. Using cysteine mutants we also assessed the role of disulphide bridge formation in the folding and stability of CAH1. We found that a disulphide bridge between cysteines at positions 27 and 191 in the mature protein was required for correct folding of the protein. Using a mass spectrometric approach we were able to measure the enzymatic activity of CAH1 protein. Under circumstances where protein N-glycosylation is blocked in vivo, the activity of CAH1 is completely inhibited.

Conclusions/Significance

We show for the first time the importance of post-translational modifications such as N-glycosylation and intramolecular disulphide bridge formation in folding and trafficking of a protein from the secretory pathway to the chloroplast in higher plants. Requirements for these post-translational modifications for a fully functional native protein explain the need for an alternative route to the chloroplast.     

蓝藻的蛋白质翻译后修饰研究进展

蛋白质翻译后修饰系统几乎参与了细胞所有的正常生命活动过程,并发挥着重要的调控作用。目前,基于生物质谱技术进行蛋白质翻译后修饰的规模化分析鉴定,已经成为蛋白质组学研究的核心内容之一。近年来的研究表明,蓝藻细胞中存在着复杂的蛋白质翻译后修饰系统,如磷酸化,乙酰化,甲基化,糖基化,氧化等,这些翻译后修饰在蓝藻细胞的代谢过程中可能发挥着重要的调控作用。本文主要针对蓝藻细胞中蛋白质翻译后修饰的发现与鉴定,以及翻译后修饰潜在的生物学功能展开简要综述。     

Post-translational modifications of the polycystin proteins

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of kidney failure and affects up to 12 million people worldwide. Germline mutations in two genes, PKD1 or PKD2, account for almost all patients with ADPKD. The ADPKD proteins, polycystin-1 (PC1) and polycystin-2 (PC2), are regulated by post-translational modifications (PTM), with phosphorylation, glycosylation and proteolytic cleavage being the best described changes. A few PTMs have been shown to regulate polycystin trafficking, signalling, localisation or stability and thus their physiological function. A key challenge for the future will be to elucidate the functional significance of all the individual PTMs reported to date. Finally, it is possible that site-specific mutations that disrupt PTM could contribute to cystogenesis although in the majority of cases, confirmatory evidence is awaited.     

Structure and synthesis of polyisoprenoids used in N-glycosylation across the three domains of life

N-linked protein glycosylation was originally thought to be specific to eukaryotes, but evidence of this post-translational modification has now been discovered across all domains of life: Eucarya, Bacteria, and Archaea. In all cases, the glycans are first assembled in a step-wise manner on a polyisoprenoid carrier lipid. At some stage of lipid-linked oligosaccharide synthesis, the glycan is flipped across a membrane. Subsequently, the completed glycan is transferred to specific asparagine residues on the protein of interest. Interestingly, though the N-glycosylation pathway seems to be conserved, the biosynthetic pathways of the polyisoprenoid carriers, the specific structures of the carriers, and the glycan residues added to the carriers vary widely. In this review we will elucidate how organisms in each basic domain of life synthesize the polyisoprenoids that they utilize for N-linked glycosylation and briefly discuss the subsequent modifications of the lipid to generate a lipid-linked oligosaccharide.     

Pre- and post-translational regulation of osteopontin in cancer

Osteopontin (OPN) is a matricellular protein that binds to a number of cell surface receptors including integrins and CD44. It is expressed in many tissues and secreted into body fluids including blood, milk and urine. OPN plays important physiological roles in bone remodeling, immune response and inflammation. It is also a tumour-associated protein, and elevated OPN levels are associated with tumour formation, progression and metastasis. Research has revealed a promising role for OPN as a cancer biomarker. OPN is subject to alternative splicing, as well as post-translational modifications such as phosphorylation, glycosylation and proteolytic cleavage. Functional differences have been revealed for different isoforms and post-translational modifications. The pattern of isoform expression and post-translational modification is cell-type specific and may influence the potential role of OPN in malignancy and as a cancer biomarker.     

蛋白质糖基化修饰的研究方法及其应用

蛋白质糖基化是一种重要的翻译后修饰,它参与和调控生物体的许多生命活动。随着蛋白质组技术的不断发展,蛋白质糖基化研究越来越受到广泛的重视。本文介绍了蛋白质糖基化修饰的研究内容与方法,并综述了最近的研究进展。     

Modifying Post-Translational Modifications: A Strategy Used by Archaea for Adapting to Changing Environments?

In concert with the selective pressures affecting protein folding and function in the extreme environments in which they can exist, proteins in Archaea have evolved to present permanent molecular adaptations at the amino acid sequence level. Such adaptations may not, however, suffice when Archaea encounter transient changes in their surroundings. Post-translational modifications offer a rapid and reversible layer of adaptation for proteins to cope with such situations. Here, it is proposed that Archaea further augment their ability to survive changing growth conditions by modifying the extent, position, and, where relevant, the composition of different post-translational modifications, as a function of the environment. Support for this hypothesis comes from recent reports describing how patterns of protein glycosylation, methylation, and other post-translational modifications of archaeal proteins are altered in response to environmental change. Indeed, adjusting post-translational modifications as a means to cope with environmental variability may also hold true beyond the Archaea.     

Caloric excess or restriction mediated modulation of metabolic enzyme acetylation-proposed effects on cardiac growth and function

Caloric excess has been postulated to disrupt cardiac function via (i) the generation of toxic intermediates, (ii) via protein glycosylation and (iii) through the generation of reactive oxygen species. It is now increasingly being recognized that the nutrient intermediates themselves may modulate metabolic pathways through the post-translational modifications of metabolic enzymes. In light of the high energy demand of the heart, these nutrient mediated modulations in metabolic pathway functioning may play an important role in cardiac function and in the capacity of the heart to adapt to biomechanical stressors. In this review the role of protein acetylation and deacetylation in the control of metabolic programs is explored. Although not extensively investigated directly in the heart, the emerging data support that these nutrient mediated post-translational regulatory events (i) modulate cardiac metabolic pathways, (ii) integrate nutrient flux mediated post-translational effects with cardiac function and (iii) may be important in the development of cardiac pathology. Areas of investigation that need to be explored are highlighted. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.     

Caloric excess or restriction mediated modulation of metabolic enzyme acetylation—proposed effects on cardiac growth and function

Caloric excess has been postulated to disrupt cardiac function via (i) the generation of toxic intermediates, (ii) via protein glycosylation and (iii) through the generation of reactive oxygen species. It is now increasingly being recognized that the nutrient intermediates themselves may modulate metabolic pathways through the post-translational modifications of metabolic enzymes. In light of the high energy demand of the heart, these nutrient mediated modulations in metabolic pathway functioning may play an important role in cardiac function and in the capacity of the heart to adapt to biomechanical stressors. In this review the role of protein acetylation and deacetylation in the control of metabolic programs is explored. Although not extensively investigated directly in the heart, the emerging data support that these nutrient mediated post-translational regulatory events (i) modulate cardiac metabolic pathways, (ii) integrate nutrient flux mediated post-translational effects with cardiac function and (iii) may be important in the development of cardiac pathology. Areas of investigation that need to be explored are highlighted. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.     

tau蛋白异常翻译后修饰在阿尔茨海默病中的作用

在阿尔茨海默病（A1zheimer’s disease,AD）中微管相关蛋白tau能够产生许多异常翻译后修饰并聚集形成配对螺旋丝（paired helical filament,PHF）。这些tau的修饰包括过磷酸化、异常糖基化、截断等,其中,过磷酸化和异常糖基化是阿尔茨海默氏病等神经退行性疾病神经元纤维化的主要分子发病机制。     

Nitric oxide signalling via cytoskeleton in plants

Nitric oxide (NO) in plant cell mediates processes of growth and development starting from seed germination to pollination, as well as biotic and abiotic stress tolerance. However, proper understanding of the molecular mechanisms of NO signalling in plants has just begun to emerge. Accumulated evidence suggests that in eukaryotic cells NO regulates functions of proteins by their post-translational modifications, namely tyrosine nitration and S-nitrosylation. Among the candidates for NO-downstream effectors are cytoskeletal proteins because of their involvement in many processes regulated by NO. This review discusses new insights in plant NO signalling focused mainly on the involvement of cytoskeleton components into NO-cascades. Herein, examples of NO-related post-translational modifications of cytoskeletal proteins, and also indirect NO impact, are discussed. Special attention is paid to plant α-tubulin tyrosine nitration as an emerging topic in plant NO research.