Infancy-onset diabetes caused by de-regulated AMPylation of the human endoplasmic reticulum chaperone BiP

Dysfunction of the endoplasmic reticulum (ER) in insulin-producing beta cells results in cell loss and diabetes mellitus. Here we report on five individuals from three different consanguineous families with infancy-onset diabetes mellitus and severe neurodevelopmental delay caused by a homozygous p.(Arg371Ser) mutation in FICD. The FICD gene encodes a bifunctional Fic domain-containing enzyme that regulates the ER Hsp70 chaperone, BiP, via catalysis of two antagonistic reactions: inhibitory AMPylation and stimulatory deAMPylation of BiP. Arg371 is a conserved residue in the Fic domain active site. The FICD^R371S mutation partially compromises BiP AMPylation in vitro but eliminates all detectable deAMPylation activity. Overexpression of FICD^R371S or knock-in of the mutation at the FICD locus of stressed CHO cells results in inappropriately elevated levels of AMPylated BiP and compromised secretion. These findings, guided by human genetics, highlight the destructive consequences of de-regulated BiP AMPylation and raise the prospect of tuning FICD's antagonistic activities towards therapeutic ends.

Analysis of lysine acetylation in tomato spot wilt virus infection in Nicotiana benthamiana

Introduction

Kac is a model for all acylation modification studies. Kac plays a critical role in eukaryotes and prokaryotes. It is mainly involved in six major biological functions: gene expression, signal transduction, cell development, protein conversion, metabolism, and metabolite transport.

Method

We investigated and compared the acetylation modification of proteins in healthy and tomato spot wilt virus (TSWV)-infected Nicotiana benthamiana leaves.

Result

We identified 3,418 acetylated lysine sites on 1962 proteins acetylation of proteins in the TSWV-infected and control groups were compared; it was observed that 408 sites on 294 proteins were upregulated and 284 sites on 219 proteins (involved in pentose phosphate, photosynthesis, and carbon fixation in photosynthesis) were downregulated after the infection. Overall, 35 conserved motifs were identified, of which xxxkxxxxx_K_ Rxxxxxxxxx represented 1,334 (31.63%) enrichment motifs and was the most common combination. Bioinformatic analysis revealed that most of the proteins with Kac sites were located in the chloroplast and cytoplasm. They were involved in biological processes, such as cellular and metabolic processes.

Discussion

In conclusion, our results revealed that Kac may participate in the regulation of TSWV infection in N. benthamiana.

Arginine methylation sites on SepIVA help balance elongation and septation in Mycobacterium smegmatis

The growth of mycobacterial cells requires successful coordination between elongation and septation. However, it is not clear which factors mediate this coordination. Here, we studied the function and post-translational modification of an essential division factor, SepIVA, in Mycobacterium smegmatis. We find that SepIVA is arginine methylated, and that alteration of its methylation sites affects both septation and polar elongation of Msmeg. Furthermore, we show that SepIVA regulates the localization of MurG and that this regulation may impact polar elongation. Finally, we map SepIVA's two regulatory functions to different ends of the protein: the N-terminus regulates elongation while the C-terminus regulates division. These results establish SepIVA as a regulator of both elongation and division and characterize a physiological role for protein arginine methylation sites for the first time in mycobacteria.

Histone acetylation at the sulfotransferase 1a1 gene is associated with its hepatic expression in normal aging

OBJECTIVES

Phase II drug metabolism is poorly studied in advanced age and older adults may exhibit significant variability in their expression of phase II enzymes. We hypothesized that age-related changes to epigenetic regulation of genes involved in phase II drug metabolism may contribute to these effects.

METHODS

We examined published epigenome-wide studies of human blood and identified the SULT1A1 and UGT1A6 genes as the top loci showing epigenetic changes with age. To assess possible functional alterations with age in the liver, we assayed DNA methylation (5mC) and histone acetylation changes around the mouse homologs Sult1a1 and Ugt1a6 in liver tissue from mice aged 4-32 months.

RESULTS

Our sample shows a significant loss of 5mC at Sult1a1 (β = -1.08, 95% CI [-1.8, -0.2], SE = 0.38, P = 0.011), mirroring the loss of 5mC with age observed in human blood DNA at the same locus. We also detected increased histone 3 lysine 9 acetylation (H3K9ac) with age at Sult1a1 (β = 0.11, 95% CI [0.002, 0.22], SE = 0.05, P = 0.04), but no change to histone 3 lysine 27 acetylation (H3K27ac). Sult1a1 gene expression is significantly positively associated with H3K9ac levels, accounting for 23% of the variation in expression. We did not detect any significant effects at Ugt1a6.

CONCLUSIONS

Sult1a1 expression is under epigenetic influence in normal aging and this influence is more pronounced for H3K9ac than DNA methylation or H3K27ac in this study. More generally, our findings support the relevance of epigenetics in regulating key drug-metabolizing pathways. In the future, epigenetic biomarkers could prove useful to inform dosing in older adults.

The Role of Post-Translational Modifications of Chemokines by CD26 in Cancer

Chemokines are a large family of small chemotactic cytokines that fulfill a central function in cancer. Both tumor-promoting and -impeding roles have been ascribed to chemokines, which they exert in a direct or indirect manner. An important post-translational modification that regulates chemokine activity is the NH₂-terminal truncation by peptidases. CD26 is a dipeptidyl peptidase (DPPIV), which typically clips a NH₂-terminal dipeptide from the chemokine. With a certain degree of selectivity in terms of chemokine substrate, CD26 only recognizes chemokines with a penultimate proline or alanine. Chemokines can be protected against CD26 recognition by specific amino acid residues within the chemokine structure, by oligomerization or by binding to cellular glycosaminoglycans (GAGs). Upon truncation, the binding affinity for receptors and GAGs is altered, which influences chemokine function. The consequences of CD26-mediated clipping vary, as unchanged, enhanced, and reduced activities are reported. In tumors, CD26 most likely has the most profound effect on CXCL12 and the interferon (IFN)-inducible CXCR3 ligands, which are converted into receptor antagonists upon truncation. Depending on the tumor type, expression of CD26 is upregulated or downregulated and often results in the preferential generation of the chemokine isoform most favorable for tumor progression. Considering the tight relationship between chemokine sequence and chemokine binding specificity, molecules with the appropriate characteristics can be chemically engineered to provide innovative therapeutic strategies in a cancer setting.

Machine Learning Methods in Prediction of Protein Palmitoylation Sites: A Brief Review

Protein palmitoylation is a fundamental and reversible post-translational lipid modification that involves a series of biological processes. Although a large number of experimental studies have explored the molecular mechanism behind the palmitoylation process, the computational methods has attracted much attention for its good performance in predicting palmitoylation sites compared with expensive and time-consuming biochemical experiments. The prediction of protein palmitoylation sites is helpful to reveal its biological mechanism. Therefore, the research on the application of machine learning methods to predict palmitoylation sites has become a hot topic in bioinformatics and promoted the development in the related fields. In this review, we briefly introduced the recent development in predicting protein palmitoylation sites by using machine learningbased methods and discussed their benefits and drawbacks. The perspective of machine learning-based methods in predicting palmitoylation sites was also provided. We hope the review could provide a guide in related fields.

Reverse-Phase Protein Array: Technology, Application, Data Processing, and Integration

Reverse-phase protein array (RPPA) is a high-throughput antibody-based targeted proteomics platform that can quantify hundreds of proteins in thousands of samples derived from tissue or cell lysates, serum, plasma, or other body fluids. Protein samples are robotically arrayed as microspots on nitrocellulose-coated glass slides. Each slide is probed with a specific antibody that can detect levels of total protein expression or post-translational modifications, such as phosphorylation as a measure of protein activity. Here we describe workflow protocols and software tools that we have developed and optimized for RPPA in a core facility setting that includes sample preparation, microarray mapping and printing of protein samples, antibody labeling, slide scanning, image analysis, data normalization and quality control, data reporting, statistical analysis, and management of data. Our RPPA platform currently analyzes ∼240 validated antibodies that primarily detect proteins in signaling pathways and cellular processes that are important in cancer biology. This is a robust technology that has proven to be of value for both validation and discovery proteomic research and integration with other omics data sets.

Reverse-Phase Protein Array: Technology, Application, Data Processing, and Integration

Reverse-phase protein array (RPPA) is a high-throughput antibody-based targeted proteomics platform that can quantify hundreds of proteins in thousands of samples derived from tissue or cell lysates, serum, plasma, or other body fluids. Protein samples are robotically arrayed as microspots on nitrocellulose-coated glass slides. Each slide is probed with a specific antibody that can detect levels of total protein expression or post-translational modifications, such as phosphorylation as a measure of protein activity. Here we describe workflow protocols and software tools that we have developed and optimized for RPPA in a core facility setting that includes sample preparation, microarray mapping and printing of protein samples, antibody labeling, slide scanning, image analysis, data normalization and quality control, data reporting, statistical analysis, and management of data. Our RPPA platform currently analyzes ∼240 validated antibodies that primarily detect proteins in signaling pathways and cellular processes that are important in cancer biology. This is a robust technology that has proven to be of value for both validation and discovery proteomic research and integration with other omics data sets.

Apple BT2 protein negatively regulates jasmonic acid-triggered leaf senescence by modulating the stability of MYC2 and JAZ2

Jasmonic acid (JA) is shown to induce leaf senescence. However, the underlying molecular mechanism is not well understood, especially in woody plants such as fruit trees. In this study, we are interested in exploring the biological role of MdBT2 in JA-mediated leaf senescence. We found that MdBT2 played an antagonistic role in MdMYC2-promoted leaf senescence. Our results revealed that MdBT2 interacted with MdMYC2 and accelerated its ubiquitination degradation, thus negatively regulated MdMYC2-promoted leaf senescence. In addition, MdBT2 acted as a stabilizing factor to improve the stability of MdJAZ2 through direct interaction, thereby inhibited JA-mediated leaf senescence. Furthermore, our results also showed that MdBT2 interacted with a subset of JAZ proteins in apple, including MdJAZ1, MdJAZ3, MdJAZ4 and MdJAZ8. Our investigations provide new insight into molecular mechanisms of JA-modulated leaf senescence. The dynamic JA-MdBT2-MdJAZ2-MdMYC2 regulatory module plays an important role in JA-modulated leaf senescence.

It's Morphin' time: how multiple signals converge on ARF transcription factors to direct development

Plant development programs are constantly updated by information about environmental conditions, currently available resources, and sites of active organogenesis. Much of this information is encoded in modifications of transcription factors that lead to changes in their relative abundance, activity and localization. Recent work on the Auxin Response Factor family of transcription factors has highlighted the large diversity of such modifications, as well as how they may work synergistically or antagonistically to regulate downstream responses. ARFs can be regulated by alternative splicing, post-translational modification, and subcellular localization, among many other mechanisms. Beyond the many ways ARFs themselves can be regulated, they can also act cooperatively with other transcription factors to enable highly complex genetic networks with distinct developmental outcomes. Multi-level regulation like what has been documented for ARFs has the capacity to generate flexibility in transcriptional outputs, as well as resilience to short-term perturbations.

Diurnal Differences in Human Muscle Isometric Force In Vivo Are Associated with Differential Phosphorylation of Sarcomeric M-Band Proteins

We investigated whether diurnal differences in muscle force output are associated with the post-translational state of muscle proteins. Ten physically active men (mean ± SD; age 26.7 ± 3.7 y) performed experimental sessions in the morning (08:00 h) and evening (17:00 h), which were counterbalanced in order of administration and separated by at least 72 h. Knee extensor maximal voluntary isometric contraction (MVIC) force and peak rate of force development (RFD) were measured, and samples of vastus lateralis were collected immediately after exercise. MVIC force was greater in the evening (mean difference of 67 N, 10.2%; p < 0.05). Two-dimensional (2D) gel analysis encompassed 122 proteoforms and discovered 6 significant (p < 0.05; false discovery rate [FDR] = 10%) diurnal differences. Phosphopeptide analysis identified 1693 phosphopeptides and detected 140 phosphopeptides from 104 proteins that were more (p < 0.05, FDR = 22%) phosphorylated in the morning. Myomesin 2, muscle creatine kinase, and the C-terminus of titin exhibited the most robust (FDR < 10%) diurnal differences. Exercise in the morning, compared to the evening, coincided with a greater phosphorylation of M-band-associated proteins in human muscle. These protein modifications may alter the M-band structure and disrupt force transmission, thus potentially explaining the lower force output in the morning.

Mannose Binding Lectin Is Hydroxylated by Collagen Prolyl-4-hydroxylase and Inhibited by Some PHD Inhibitors

Background

Mannose-binding lectin (MBL) is an important component of innate immune defense. MBL undergoes oligomerization to generate high mol weight (HMW) forms which act as pattern recognition molecules to detect and opsonize various microorganisms. Several post-translational modifications including prolyl hydroxylation are known to affect the oligomerization of MBL. Yet, the enzyme(s) which hydroxylate proline in the collagen-like domain residues have not been identified and the significance of prolyl hydroxylation is incompletely understood.

Methods

To investigate post-translational modifications of MBL, we stably expressed Myc-DDK tagged MBL in HEK293S cells. We used pharmacologic and genetic inhibition of 2-oxoglutarate-dependent dioxygenases (2OGDD) to identify the enzyme required for prolyl hydroxylation of MBL. We performed mass spectrometry to determine the effects of various inhibitors on MBL modifications.

Results

Secretion of HMW MBL was impaired by inhibitors of the superfamily of 2OGDD, and was dependent on prolyl-4-hydroxylase subunit α1. Roxadustat and vadadustat, but not molidustat, led to significant suppression of hydroxylation and secretion of HMW forms of MBL.

Conclusions

These data suggest that prolyl hydroxylation in the collagen-like domain of MBL is mediated by collagen prolyl-4-hydroxylase. Reduced MBL activity is likely to be an off-target effect of some, but not all, prolyl hydroxylase domain (PHD) inhibitors. There may be advantages in selective PHD inhibitors that would not interfere with MBL production.

Regulation of mitophagy by the ubiquitin pathway in neurodegenerative diseases

Mitophagy is a cellular process by which dysfunctional mitochondria are degraded via autophagy. Increasing empirical evidence proposes that this mitochondrial quality-control mechanism is defective in neurons of patients with various neurodegenerative diseases such as Ataxia Telangiectasia, Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis. Accumulation of defective mitochondria and the production of reactive oxygen species due to defective mitophagy have been identified as causes underlying neurodegenerative disease pathogenesis. However, the reason mitophagy is defective in most neurodegenerative diseases is unclear. Like mitophagy, defects in the ubiquitin/26S proteasome pathway have been linked to neurodegeneration, resulting in the characteristic protein aggregates often seen in neurons of affected patients. Although initiation of mitophagy requires a functional ubiquitin pathway, whether defects in the ubiquitin pathway are causally responsible for defective mitophagy is not known. In this mini-review, we introduce mitophagy and ubiquitin pathways and provide a summary of our current understanding of the regulation of mitophagy by the ubiquitin pathway. We will then briefly review empirical evidence supporting mitophagy defects in neurodegenerative diseases. The review will conclude with a discussion of the constitutively elevated expression of ubiquitin-like protein Interferon-Stimulated Gene 15 (ISG15), an antagonist of the ubiquitin pathway, as a potential cause of defective mitophagy in neurodegenerative diseases. Impact statement Neurodegenerative diseases place an enormous burden on patients and caregivers globally. Over six million people in the United States alone suffer from neurodegenerative diseases, all of which are chronic, incurable, and with causes unknown. Identifying a common molecular mechanism underpinning neurodegenerative disease pathology is urgently needed to aid in the design of effective therapies to ease suffering, reduce economic cost, and improve the quality of life for these patients. Although the development of neurodegeneration may vary between neurodegenerative diseases, they have common cellular hallmarks, including defects in the ubiquitin-proteasome system and mitophagy. In this review, we will provide a summary of our current understanding of the regulation of mitophagy by the ubiquitin pathway and discuss the potential of targeting mitophagy and ubiquitin pathways for the treatment of neurodegeneration.

Post-translational modifications of high mobility group box 1 and cancer

Post-translational modifications (PTMs) of High mobility group box 1 (HMGB1) have not been investigated as extensively as those of other HMG proteins but accumulating evidence has shown the remarkable biological significances induced by the post-translational: acetylation, methylation and phosphorylation, oxidation, glycosylation and ADP-ribosylation of the HMGB1 to modulate its interactions with DNA and other proteins. Although HMGB1 is localized in the nucleus in almost all cells at baseline, it can be rapidly mobilized to other sites within the cell, including the cytoplasm and mitochondria, as well as into the extracellular; hence there is an increasing interest by researches into the complex relationship between the PTMs of HMGB1 protein and its diverse biological activities. The PTMs of HMGB1 could also have effects on gene expression following changes in its DNA-binding properties and in extracellular environment displays immunological activity and could serve as a potential target for new therapy. Our reviewed identifies covalent modifications of HMGB1, and highlighted how these PTMs affect the functions of HMGB1 protein in a variety of cellular and extra cellular processes as well as diseases and therapy.

Engineering oxidative stability in human hemoglobin based on the Hb providence (βK82D) mutation and genetic cross-linking

Previous work suggested that hemoglobin (Hb) tetramer formation slows autoxidation and hemin loss and that the naturally occurring mutant, Hb Providence (HbProv; βK82D), is much more resistant to degradation by H₂O₂ We have examined systematically the effects of genetic cross-linking of Hb tetramers with and without the HbProv mutation on autoxidation, hemin loss, and reactions with H₂O₂, using native HbA and various wild-type recombinant Hbs as controls. Genetically cross-linked Hb Presbyterian (βN108K) was also examined as an example of a low oxygen affinity tetramer. Our conclusions are: (a) at low concentrations, all the cross-linked tetramers show smaller rates of autoxidation and hemin loss than HbA, which can dissociate into much less stable dimers and (b) the HbProv βK82D mutation confers more resistance to degradation by H₂O₂, by markedly inhibiting oxidation of the β93 cysteine side chain, particularly in cross-linked tetramers and even in the presence of the destabilizing Hb Presbyterian mutation. These results show that cross-linking and the βK82D mutation do enhance the resistance of Hb to oxidative degradation, a critical element in the design of a safe and effective oxygen therapeutic.

An outlook on protein S-acylation in plants: what are the next steps?

S-acylation, also known as palmitoylation, is the reversible post-translational addition of fatty acids to proteins. Historically thought primarily to be a means for anchoring otherwise soluble proteins to membranes, evidence now suggests that reversible S-acylation may be an important dynamic regulatory mechanism. Importantly S-acylation affects the function of many integral membrane proteins, making it an important factor to consider in understanding processes such as cell wall synthesis, membrane trafficking, signalling across membranes and regulating ion, hormone and metabolite transport through membranes. This review summarises the latest thoughts, ideas and findings in the field as well discussing future research directions to gain a better understanding of the role of this enigmatic regulatory protein modification.

Post-translational Activation of Glutamate Cysteine Ligase with Dimercaprol: A NOVEL MECHANISM OF INHIBITING NEUROINFLAMMATION IN VITRO

Neuroinflammation and oxidative stress are hallmarks of various neurological diseases. However, whether and how the redox processes control neuroinflammation is incompletely understood. We hypothesized that increasing cellular glutathione (GSH) levels would inhibit neuroinflammation. A series of thiol compounds were identified to elevate cellular GSH levels by a novel approach (i.e. post-translational activation of glutamate cysteine ligase (GCL), the rate-limiting enzyme in GSH biosynthesis). These small thiol-containing compounds were examined for their ability to increase intracellular GSH levels in a murine microglial cell line (BV2), of which dimercaprol (2,3-dimercapto-1-propanol (DMP)) was found to be the most effective compound. DMP increased GCL activity and decreased LPS-induced production of pro-inflammatory cytokines and inducible nitric-oxide synthase induction in BV2 cells in a concentration-dependent manner. The ability of DMP to elevate GSH levels and attenuate LPS-induced pro-inflammatory cytokine production was inhibited by buthionine sulfoximine, an inhibitor of GCL. DMP increased the expression of GCL holoenzyme without altering the expression of its subunits or Nrf2 target proteins (NQO1 and HO-1), suggesting a post-translational mechanism. DMP attenuated LPS-induced MAPK activation in BV2 cells, suggesting the MAPK pathway as the signaling mechanism underlying the effect of DMP. Finally, the ability of DMP to increase GSH via GCL activation was observed in mixed cerebrocortical cultures and N27 dopaminergic cells. Together, the data demonstrate a novel mechanism of GSH elevation by post-translational activation of GCL. Post-translational activation of GCL offers a novel targeted approach to control inflammation in chronic neuronal disorders associated with impaired adaptive responses.

Tau physiology and pathomechanisms in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) has been associated with toxic intracellular aggregates of hyperphosphorylated tau (FTLD‐tau). Moreover, genetic studies identified mutations in the MAPT gene encoding tau in familial cases of the disease. In this review, we cover a range of aspects of tau function, both in the healthy and diseased brain, discussing several in vitro and in vivo models. Tau structure and function in the healthy brain is presented, accentuating its distinct compartmentalization in neurons and its role in microtubule stabilization and axonal transport. Furthermore, tau‐driven pathology is discussed, introducing current concepts and the underlying experimental evidence. Different aspects of pathological tau phosphorylation, the protein's genomic and domain organization as well as its spreading in disease, together with MAPT‐associated mutations and their respective models are presented. Dysfunction related to other post‐transcriptional modifications and their effect on normal neuronal functions such as cell cycle, epigenetics and synapse dynamics are also discussed, providing a mechanistic explanation for the observations made in FTLD‐tau cases, with the possibility for therapeutic intervention.

In this review, we cover aspects of tau function, both in the healthy and diseased brain, referring to different in vitro and in vivo models. In healthy neurons, tau is compartmentalized, with higher concentrations found in the distal part of the axon. Cargo molecules are sensitive to this gradient. A disturbed tau distribution, as found in frontotemporal lobar degeneration (FTLD‐tau), has severe consequences for cellular physiology: tau accumulates in the neuronal soma and dendrites, leading among others to microtubule depolymerization and impaired axonal transport. Tau forms insoluble aggregates that sequester additional molecules stalling cellular physiology. Neuronal communication is gradually lost as toxic tau accumulates in dendritic spines with subsequent degeneration of synapses and synaptic loss. Thus, by providing a mechanistic explanation for the observations made in FTLD‐tau cases, arises a possibility for therapeutic interventions.

This article is part of the Frontotemporal Dementia special issue.

Posttranslational protein modifications by reactive nitrogen and chlorine species and strategies for their prevention and elimination

Proteins are subject to various posttranslational modifications, some of them being undesired from the point of view of metabolic efficiency. Prevention of such modifications is expected to provide new means of therapy of diseases and decelerate the process of aging. In this review, modifications of proteins by reactive nitrogen species and reactive halogen species, is briefly presented and means of prevention of these modifications and their sequelae are discussed, including the denitrase activity and inhibitors of myeloperoxidase.

Post-translational regulation of endothelial nitric oxide synthase in vascular endothelium

Nitric oxide (NO) is a short-lived gaseous signaling molecule. In blood vessels, it is synthesized in a dynamic fashion by endothelial nitric oxide synthase (eNOS) and influences vascular function via two distinct mechanisms, the activation of soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP)-dependent signaling and the S-nitrosylation of proteins with reactive thiols (S-nitrosylation). The regulation of eNOS activity and NO bioavailability is critical to maintain blood vessel function. The activity of eNOS and ability to generate NO is regulated at the transcriptional, posttranscriptional, and posttranslational levels. Post-translational modifications acutely impact eNOS activity and dysregulation of these mechanisms compromise eNOS activity and foster the development of cardiovascular diseases (CVDs). This review will intergrate past and current literature on the post-translational modifications of eNOS in both health and disease.

Thiol-based redox control of enzymes involved in the tetrapyrrole biosynthesis pathway in plants

The last decades of research brought substantial insights into tetrapyrrole biosynthetic pathway in photosynthetic organisms. Almost all genes have been identified and roles of seemingly all essential proteins, leading to the synthesis of heme, siroheme, phytochromobilin, and chlorophyll (Chl), have been characterized. Detailed studies revealed the existence of a complex network of transcriptional and post-translational control mechanisms for maintaining a well-adjusted tetrapyrrole biosynthesis during plant development and adequate responses to environmental changes. Among others one of the known post-translational modifications is regulation of enzyme activities by redox modulators. Thioredoxins and NADPH-dependent thioredoxin reductase C (NTRC) adjust the activity of tetrapyrrole synthesis to the redox status of plastids. Excessive excitation energy of Chls in both photosystems and accumulation of light-absorbing unbound tetrapyrrole intermediates generate reactive oxygen species, which interfere with the plastid redox poise. Recent reports highlight ferredoxin-thioredoxin and NTRC-dependent control of key steps in tetrapyrrole biosynthesis in plants. In this review we introduce the regulatory impact of these reductants on the stability and activity of enzymes involved in 5-aminolevulinic acid synthesis as well as in the Mg-branch of the tetrapyrrole biosynthetic pathway and we propose molecular mechanisms behind this redox control.

A conserved archaeal pathway for tail-anchored membrane protein insertion

Eukaryotic tail-anchored (TA) membrane proteins are inserted into the endoplasmic reticulum by a post-translational TRC40 pathway, but no comparable pathway is known in other domains of life. The crystal structure of an archaebacterial TRC40 sequence homolog bound to ADP•AlF(4) (-) reveals characteristic features of eukaryotic TRC40, including a zinc-mediated dimer and a large hydrophobic groove. Moreover, archaeal TRC40 interacts with the transmembrane domain of TA substrates and directs their membrane insertion. Thus, the TRC40 pathway is more broadly conserved than previously recognized.

Variable domain I of nematode CLEs directs post-translational targeting of CLE peptides to the extracellular space

Effector proteins expressed in the esophageal gland cells of cyst nematodes are delivered into plant cells through a hollow, protrusible stylet. Although evidence indicates that effector proteins function in the cytoplasm of the syncytium, technical constraints have made it difficult to directly determine where nematode effector proteins are initially delivered: cytoplasm, extracellular space, or both. Recently, we demonstrated that soybean cyst nematode CLE (HgCLE) propeptides are delivered to the cytoplasm of syncytial cells. Genetic and biochemical analyses indicate that the variable domain (VD) sequence is then required for targeting cytoplasmically delivered nematode CLEs to the apoplast where they function as ligand mimics of endogenous plant CLE peptides. The fact that nematode CLEs are targeted through the gland cell secretory pathway and delivered as mature propeptides into plant cells makes it impossible for these proteins to be subsequently delivered to the extracellular space via co-translational translocation through the endoplasmic reticulum (ER) secretory pathway of the host cell. However, when expressed in transgenic plants, if the mature nematode CLE propeptide harbored a functional cryptic signal peptide, it could possibly traffic to the apoplast through the ER secretory pathway by co-translational translocation. Here, we present evidence that VDI, the N-terminal sequence of the variable domain of HgCLE2, is sufficient for trafficking CLE peptides to the apoplast and that trafficking is indeed through an alternative pathway other than co-translational translocation.

[Viruses and telomerase]

The involvement of viral infections in the genesis of cancers is currently established. However, the narrow correlation between viruses and the activation of telomerase was defined only recently. The telomerase activity is detected in more than 85 % of human cancers and would take part to immortalization processes, associated with cellular transformation. The active minimal complex of telomerase is composed of a RNA subunit comprising a template sequence which is reverse-transcribed onto telomeres by a proteic component TERT. A disregulation of telomerase activity was observed consecutively to infection by viruses from various families. This phenomenon would mainly rest on modulation of the expression and the nuclear targeting of TERT by viral proteins or further to viral genome integrations close to the TERT gene. Moreover, the Marek's Disease herpesvirus, responsible of T-lymphomas in chickens, is particular in that it encodes, within its genome, a viral telomerase RNA subunit, vTR, which induces a more greater telomerase activity than its avian cellular counterpart, cTR.

Reaction of phosphorylated and O-glycosylated peptides by chemically targeted identification at ambient temperature

Conditions for carrying out chemically targeted identification of peptides containing phosphorylated or glycosylated serine residues have been investigated. Ba(OH)2 was used at ambient temperature to catalyze the beta-elimination reaction at 25 degrees C. Nucleophilic addition of 2-aminoethanethiol was performed in both parallel and tandem experiments. The method was demonstrated by the reaction of beta-casein tryptic digest phosphopeptides and an O-glycosylated peptide. Contrary to an earlier report by others, the glycopeptide was found to react with essentially the same kinetics as phosphopeptides. Conversion of four phosphoserines in residues 15, 17, 18, and 19 from bovine beta-casein N-terminal tryptic phosphopeptides were followed by monitoring the time course of the addition reaction. The chemistry proceeded rapidly at room temperature with a half-reaction time of 15 min. No side-reaction products were observed; however, care was taken to minimize all counter ions that either precipitate barium or neutralize the base. Digestion of the converted peptides with lysine endopeptidase identified all five phosphoserines in the beta-casein tryptic digest. Alternatively, preincubation with base followed by nucleophilic addition of the thiol was found to work satisfactorily. The use of the water-soluble hydrochloride of 2-aminoethanethiol allowed beta-elimination, nucleophilic addition, and desalting to be carried out on a micro C18 reverse phase pipette tip.