Post-translational Modification Sites Research Articles

Implications of specific lysine residues within ataxin-3 for the molecular pathogenesis of Machado-Joseph disease.

Lysine residues are one of the main sites for posttranslational modifications of proteins, and lysine ubiquitination of the Machado-Joseph disease protein ataxin-3 is implicated in its cellular function and polyglutamine expansion-dependent toxicity. Despite previously undertaken efforts, the individual roles of specific lysine residues of the ataxin-3 sequence are not entirely understood and demand further analysis. By retaining single lysine residues of otherwise lysine-free wild-type and polyglutamine-expanded ataxin-3, we assessed the effects of a site-limited modifiability on ataxin-3 protein levels, aggregation propensity, localization, and stability. We confirmed earlier findings that levels of lysine-free ataxin-3 are reduced due to its decreased stability, which led to a diminished load of SDS-insoluble species of its polyglutamine-expanded form. The isolated presence of several single lysine residues within the N-terminus of polyglutamine-expanded ataxin-3 significantly restored its aggregate levels, with highest fold changes induced by the presence of lysine 8 or lysine 85, respectively. Ataxin-3 lacking all lysine residues presented a slightly increased nuclear localization, which was counteracted by the reintroduction of lysine 85, whereas presence of either lysine 8 or lysine 85 led to a significantly higher ataxin-3 stability. Moreover, lysine-free ataxin-3 showed increased toxicity and binding to K48-linked polyubiquitin chains, whereas the reintroduction of lysine 85, located between the ubiquitin-binding sites 1 and 2 of ataxin-3, normalized its binding affinity. Overall, our data highlight the relevance of lysine residues 8 and 85 of ataxin-3 and encourage further analyses, to evaluate the potential of modulating posttranslational modifications of these sites for influencing pathophysiological characteristics of the Machado-Joseph disease protein.

Comprehensive In Silico Characterization of the Coding and Non-Coding SNPs in Human Dectin-1 Gene with the Potential of High-Risk Pathogenicity Associated with Fungal Infections.

The human C-type lectin domain family 7 member A (CLEC7A) gene encodes a Dectin-1 protein that recognizes beta-1,3-linked and beta-1,6-linked glucans, which form the cell walls of pathogenic bacteria and fungi. It plays a role in immunity against fungal infections through pathogen recognition and immune signaling. This study aimed to explore the impact of nsSNPs in the human CLEC7A gene through computational tools (MAPP, PhD-SNP, PolyPhen-1, PolyPhen-2, SIFT, SNAP, and PredictSNP) to identify the most deleterious and damaging nsSNPs. Further, their effect on protein stability was checked along with conservation and solvent accessibility analysis by I-Mutant 2.0, ConSurf, and Project HOPE and post-translational modification analysis using MusiteDEEP. Out of the 28 nsSNPs that were found to be deleterious, 25 nsSNPs affected protein stability. Some SNPs were finalized for structural analysis with Missense 3D. Seven nsSNPs affected protein stability. Results from this study predicted that C54R, L64P, C120G, C120S, S135C, W141R, W141S, C148G, L155P, L155V, I158M, I158T, D159G, D159R, I167T, W180R, L183F, W192R, G197E, G197V, C220S, C233Y, I240T, E242G, and Y3D were the most structurally and functionally significant nsSNPs in the human CLEC7A gene. No nsSNPs were found in the predicted sites for post-translational modifications. In the 5' untranslated region, two SNPs, rs536465890 and rs527258220, showed possible miRNA target sites and DNA binding sites. The present study identified structurally and functionally significant nsSNPs in the CLEC7A gene. These nsSNPs may potentially be used for further evaluation as diagnostic and prognostic biomarkers.

Genomic study of TEX15 variants: prevalence and allelic heterogeneity in men with spermatogenic failure.

Introduction: Human spermatogenesis is a highly intricate process that requires the input of thousands of testis-specific genes. Defects in any of them at any stage of the process can have detrimental effects on sperm production and/or viability. In particular, the function of many meiotic proteins encoded by germ cell specific genes is critical for maturation of haploid spermatids and viable spermatozoa, necessary for fertilization, and is also extremely sensitive to even the slightest change in coding DNA. Methods: Here, using whole exome and genome approaches, we identified and reported novel, clinically significant variants in testis-expressed gene 15 (TEX15), in unrelated men with spermatogenic failure (SPGF). Results: TEX15 mediates double strand break repair during meiosis. Recessive loss-of-function (LOF) TEX15 mutations are associated with SPGF in humans and knockout male mice are infertile. We expand earlier reports documenting heterogeneous allelic pathogenic TEX15 variants that cause a range of SPGF phenotypes from oligozoospermia (low sperm) to nonobstructive azoospermia (no sperm) with meiotic arrest and report the prevalence of 0.6% of TEX15 variants in our patient cohort. Among identified possible LOF variants, one homozygous missense substitution c.6835G>A (p.Ala2279Thr) co-segregated with cryptozoospermia in a family with SPGF. Additionally, we observed numerous cases of inferred in trans compound heterozygous variants in TEX15 among unrelated individuals with varying degrees of SPGF. Variants included splice site, insertions/deletions (indels), and missense substitutions, many of which resulted in LOF effects (i.e., frameshift, premature stop, alternative splicing, or potentially altered posttranslational modification sites). Conclusion: In conclusion, we performed an extensive genomic study of familial and sporadic SPGF and identified potentially damaging TEX15 variants in 7 of 1097 individuals of our combined cohorts. We hypothesize that SPGF phenotype severity is dictated by individual TEX15 variant's impact on structure and function. Resultant LOFs likely have deleterious effects on crossover/recombination in meiosis. Our findings support the notion of increased gene variant frequency in SPGF and its genetic and allelic heterogeneity as it relates to complex disease such as male infertility.

An In silico Approach towards Finding the Cancer-Causing Mutations in Human MET Gene.

Mesenchymal-epithelial transition (MET) factor is a proto-oncogene encoding tyrosine kinase receptor with hepatocyte growth factor (HGF) or scatter factor (SF). It is found on the human chromosome number 7 and regulates the diverse cellular mechanisms of the human body. The impact of mutations occurring in the MET gene is demonstrated by their detrimental effects on normal cellular functions. These mutations can change the structure and function of MET leading to different diseases such as lung cancer, neck cancer, colorectal cancer, and many other complex syndromes. Hence, the current study focused on finding deleterious non-synonymous single nucleotide polymorphisms (nsSNPs) and their subsequent impact on the protein's structure and functions, which may contribute to the emergence of cancers. These nsSNPs were first identified utilizing computational tools like SIFT, PROVEAN, PANTHER-PSEP, PolyPhen-2, I-Mutant 2.0, and MUpro. A total of 45359 SNPs of MET gene were accumulated from the database of dbSNP, and among them, 1306 SNPs were identified as non-synonymous or missense variants. Out of all 1306 nsSNPs, 18 were found to be the most deleterious. Moreover, these nsSNPs exhibited substantial effects on structure, binding affinity with ligand, phylogenetic conservation, secondary structure, and post-translational modification sites of MET, which were evaluated using MutPred2, RaptorX, ConSurf, PSIPRED, and MusiteDeep, respectively. Also, these deleterious nsSNPs were accompanied by changes in properties of MET like residue charge, size, and hydrophobicity. These findings along with the docking results are indicating the potency of the identified SNPs to alter the structure and function of the protein, which may lead to the development of cancers. Nonetheless, Genome-wide association study (GWAS) studies and experimental research are required to confirm the analysis of these nsSNPs.

Computational Exploration of Functional and Structural Impact of Single Nucleotide Changes in DNMT3A Gene among Acute Myeloid Leukemia Patients

Acute myeloid leukemia (AML) is a blood cell malignancy of the myeloid line, characterized by fast proliferation of aberrant cells that build up in the bone marrow and blood, interfering with normal blood cell synthesis. DNMT3A is a DNA methyltransferase that plays a role in DNA methylation, an epigenetic modification associated with gene expression regulation. DNMT3A mutations are frequently found in AML and are associated with poor prognosis. Objective: To evaluate the impact of DNMT3A mutations on protein structure and function, specifically in the context of AML. Methods: SNPs of DNMT3A gene reported in AML (R882P, R882L, R882S, R882G, and R882C) were retrieved from National Centre for Biotechnology Information (NCBI) database and different in silico approaches were used to investigate how these mutations affect protein structure and function. Results: Prediction tools indicated that mutations are pathogenic affecting DNMT3A function and were found in evolutionarily conserved regions. Protein stability analysis showed that mutations reduce DNMT3A's structural stability, alter secondary structure of the protein, particularly helices, interacts with other proteins and reduce protein-protein affinity. RNA folding analysis revealed abnormal folding patterns caused by mutant, affecting protein translation. DNMT3A expression was reported to be considerably greater in AML compared to normal tissues, and mutations were associated with poor overall survival in AML patients. Methylation levels and post-translational modification sites of DNMT3A were also investigated. Conclusions: Overall, this research highlighted the negative impact of DNMT3A mutations on protein structure and function, emphasizing their importance in the development and prognosis of AML. Acute myeloid leukemia (AML) is a blood cell malignancy of the myeloid line, characterized by fast proliferation of aberrant cells that build up in the bone marrow and blood, interfering with normal blood cell synthesis. DNMT3A is a DNA methyltransferase that plays a role in DNA methylation, an epigenetic modification associated with gene expression regulation. DNMT3A mutations are frequently found in AML and are associated with poor prognosis. Objective: To evaluate the impact of DNMT3A mutations on protein structure and function, specifically in the context of AML. Methods: SNPs of DNMT3A gene reported in AML (R882P, R882L, R882S, R882G, and R882C) were retrieved from National Centre for Biotechnology Information (NCBI) database and different in silico approaches were used to investigate how these mutations affect protein structure and function. Results: Prediction tools indicated that mutations are pathogenic affecting DNMT3A function and were found in evolutionarily conserved regions. Protein stability analysis showed that mutations reduce DNMT3A's structural stability, alter secondary structure of the protein, particularly helices, interacts with other proteins and reduce protein-protein affinity. RNA folding analysis revealed abnormal folding patterns caused by mutant, affecting protein translation. DNMT3A expression was reported to be considerably greater in AML compared to normal tissues, and mutations were associated with poor overall survival in AML patients. Methylation levels and post-translational modification sites of DNMT3A were also investigated. Conclusions: Overall, this research highlighted the negative impact of DNMT3A mutations on protein structure and function, emphasizing their importance in the development and prognosis of AML.

An In Silico Functional Analysis of Non-Synonymous Single-Nucleotide Polymorphisms of Bovine CMAH Gene and Potential Implication in Pathogenesis.

The sugar molecule N-glycolylneuraminic acid (Neu5Gc) is one of the most common sialic acids discovered in mammals. Cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) catalyses the conversion of N-acetylneuraminic acid (Neu5Ac) to Neu5Gc, and it is encoded by the CMAH gene. On the one hand, food metabolic incorporation of Neu5Gc has been linked to specific human diseases. On the other hand, Neu5Gc has been shown to be highly preferred by some pathogens linked to certain bovine diseases. We used various computational techniques to perform an in silico functional analysis of five non-synonymous single-nucleotide polymorphisms (nsSNPs) of the bovine CMAH (bCMAH) gene identified from the 1000 Bull Genomes sequence data. The c.1271C>T (P424L) nsSNP was predicted to be pathogenic based on the consensus result from different computational tools. The nsSNP was also predicted to be critical based on sequence conservation, stability, and post-translational modification site analysis. According to the molecular dynamic simulation and stability analysis, all variations promoted stability of the bCMAH protein, but mutation A210S significantly promoted CMAH stability. In conclusion, c.1271C>T (P424L) is expected to be the most harmful nsSNP among the five detected nsSNPs based on the overall studies. This research could pave the way for more research associating pathogenic nsSNPs in the bCMAH gene with diseases.

Acetylated tau exacerbates learning and memory impairment by disturbing with mitochondrial homeostasis

Increased tau acetylation at K274 and K281 has been observed in the brains of Alzheimer's disease (AD) patients and animal models, and mitochondrial dysfunction are noticeable and early features of AD. However, the effect of acetylated tau on mitochondria has been unclear until now. Here, we constructed three type of tau forms, acetylated tau mutant by mutating its K274/K281 into Glutamine (TauKQ) to mimic disease-associated lysine acetylation, the non-acetylation tau mutant by mutating its K274/K281 into Arginine (TauKR) and the wild-type human full-length tau (TauWT). By overexpression of these tau forms in vivo and in vitro, we found that, TauKQ induced more severe cognitive deficits with neuronal loss, dendritic plasticity damage and mitochondrial dysfunctions than TauWT. Unlike TauWT induced mitochondria fusion, TauKQ not only induced mitochondria fission by decreasing mitofusion proteins, but also inhibited mitochondrial biogenesis via reduction of PGC-1a/Nrf1/Tfam levels. TauKR had no significant difference in the cognitive and mitochondrial abnormalities compared with TauWT. Treatment with BGP-15 rescued impaired learning and memory by attenuation of mitochondrial dysfunction, neuronal loss and dendritic complexity damage, which caused by TauKQ. Our data suggested that, acetylation at K274/281 was an important post translational modification site for tau neurotoxicity, and BGP-15 is a potential therapeutic drug for AD.

The Comparative Genomics and Network Analysis of eNOS by Using Different Bioinformatics Approaches

Background: Nitric oxide synthase (NOS) is an enzyme that catalyzes the synthesis of nitric oxide (NO) from L-arginine. It has three isoforms- (i) neuronal NOS (nNOS or NOS1), which participates in neural transmission; (ii) inducible NOS (iNOS or NOS2), which produces NO in macrophages; and (iii) endothelial NOS (eNOS or NOS3) that regulates blood pressure. The eNOS is mainly expressed in blood vessels and is a crucial regulator of endothelial homeostasis. Objective: The present study aimed to unravel the role of eNOS in different signaling pathways and its involvement as a therapeutic target in various neurodegenerative disorders. Methods: This study used various in silico methods for comprehensive genomic analysis of eNOS in 16 organisms from 7 different phyla. Prediction of conserved domains and evolutionary relationship for eNOS among 16 organisms was made. Various physical and chemical parameters, signal peptides, and transmembrane regions that helped understand its functional relevance were also studied. Results: Three transcription factor binding sites (TFBS), i.e., CP2, AR, and LDSPOLYA, were identified in human eNOS, while ATF1, T3R, and STAT1 were predicted in mouse eNOS. Transcription factors were identified for each regulatory region in human as well as mouse eNOS. eNOS protein was predicted to harbor 14 different post-translational modification (PTM) sites, most of which have phosphorylation (serine followed by threonine and tyrosine phosphorylation) followed by sumoylation and palmitoylation among all the organisms used in the current study. However, human eNOS has a relatively lower number of PTM sites for tyrosine phosphorylation. Conclusion: Structures of eNOS isoform, consistent with available biochemical and structural data, provide substantial insight into the NOS conformational changes, which give in-depth knowledge of the mechanism of eNOS, and will be helpful for better understanding the role of eNOS in pathophysiology.

Role of UCHL1 in the pathogenesis of neurodegenerative diseases and brain injury.

UCHL1 is a multifunctional protein expressed at high concentrations in neurons in the brain and spinal cord. UCHL1 plays important roles in regulating the level of cellular free ubiquitin and redox state as well as the degradation of select proteins. This review focuses on the potential role of UCHL1 in the pathogenesis of neurodegenerative diseases and brain injury and recovery. Subjects addressed in the review include 1) Normal physiological functions of UCHL1. 2) Posttranslational modification sites and splice variants that alter the function of UCHL1 and mouse models with mutations and deletions of UCHL1. 3) The hypothesized role and pathogenic mechanisms of UCHL1 in neurodegenerative diseases and brain injury. 4) Potential therapeutic strategies targeting UCHL1 in these disorders.

Computational analysis of the flexibility in the disordered linker region connecting LIM domains in cysteine-glycine-rich protein.

One of the key proteins that are present in the Z-disc of cardiac tissues, CSRP3, has been implicated in dilated and hypertrophic cardiomyopathy leading to heart failure. Although multiple cardiomyopathy-related mutations have been reported to reside on the two LIM domains and the disordered regions connecting the domains in this protein, the exact role of the disordered linker region is not clear. The linker harbors a few post-translational modification sites and is expected to be a regulatory site. We have carried out evolutionary studies on 5614 homologs spanning across taxa. We also performed molecular dynamics simulations of full-length CSRP3 to show that the length variations and conformational flexibility of the disordered linker could provide additional levels of functional modulation. Finally, we show that the CSRP3 homologs with widely different lengths of the linker regions could display diversity in their functional specifications. The present study provides a useful perspective to our understanding of the evolution of the disordered region between CSRP3 LIM domains.

The negative effect of G1958A polymorphism on MTHFD1 protein stability and HCC growth.

Methylenetetrahydrofolate dehydrogenase (MTHFD1), a key enzyme on the folate pathway, has been implicated in the tumor development of distinct types of cancers. The single nucleotide polymorphism (SNP) of 1958G > A mutation in the coding region of MTHFD1 (arginine 653 is mutated into glutamine) has been detected in a significant proportion of clinical samples of hepatocellular carcinoma (HCC). METHODS : Hepatoma cell lines, 97H and Hep3B were used. The expression of MTHFD1 and SNP mutation protein was determined by immunoblotting analysis. The protein ubiquitination of MTHFD1 was detected by immunoprecipitation analysis. The post-translational modification sites and interacting proteins of MTHFD1 in the presence of G1958A SNP were identified by mass spectrometry. Metabolic flux analysis was used to detect the synthesis of relevant metabolites sourced from serine isotope. The present study showed G1958A SNP of MTHFD1, encoding MTHFD1 R653Q, was associated with the attenuated protein stability caused by ubiquitination-mediated protein degradation. Mechanistically, MTHFD1 R653Q displayed an enhanced binding to the E3 ligase TRIM21, which was responsible for the augmented ubiquitination, and MTHFD1 K504 was identified to be the primary ubiquitination site. The subsequent metabolite analysis revealed MTHFD1 R653Q resulted in the repressed flux of serine-derived methyl group into metabolite precursors for purine synthesis, and the compromised purine synthesis was demonstrated to be responsible for the impeded growth capability in MTHFD1 R653Q-expressing cells. Moreover, the suppressive effect of MTHFD1 R653Q expression in tumorigenesis was verified by xenograft analysis, and the relationship between MTHFD1 G1958A SNP and its protein levels was revealed in clinical human liver cancer specimens. Our results uncovered an unidentified mechanism underlying of the impact of G1958A SNP on MTHFD1 protein stability and tumor metabolism in HCC. which provides a molecular basis for the according clinical management when considering MTHFD1 as a therapeutic target.

Auto-Kla: a novel web server to discriminate lysine lactylation sites using automated machine learning.

Recently, lysine lactylation (Kla), a novel post-translational modification (PTM), which can be stimulated by lactate, has been found to regulate gene expression and life activities. Therefore, it is imperative to accurately identify Kla sites. Currently, mass spectrometry is the fundamental method for identifying PTM sites. However, it is expensive and time-consuming to achieve this through experiments alone. Herein, we proposed a novel computational model, Auto-Kla, to quickly and accurately predict Kla sites in gastric cancer cells based on automated machine learning (AutoML). With stable and reliable performance, our model outperforms the recently published model in the 10-fold cross-validation. To investigate the generalizability and transferability of our approach, we evaluated the performance of our models trained on two other widely studied types of PTM, including phosphorylation sites in host cells infected with SARS-CoV-2 and lysine crotonylation sites in HeLa cells. The results show that our models achieve comparable or better performance than current outstanding models. We believe that this method will become a useful analytical tool for PTM prediction and provide a reference for the future development of related models. The web server and source code are available at http://tubic.org/Kla and https://github.com/tubic/Auto-Kla, respectively.

Post‐translational modification and phenotype

Post‐translational modification and phenotype

The impact of altered charge on huntingtin aggregation and lipid binding.

Huntington's disease (HD) is a fatal neurodegenerative disease caused by an expansion within the polyglutamine (polyQ) domain of the huntingtin protein (htt), resulting in toxic aggregation. The complex aggregation mechanism is influenced by a variety of factors, including the first 17 amino acids at the N-terminus (Nt17) preceding the polyQ domain and presence of lipid membranes. Nt17 has a propensity to form an amphipathic α-helix which promotes, through intramolecular interactions, the formation of α-helix rich oligomers in which nucleation of fibril formation occurs. The Nt17 amphipathic α-helix also facilitates htt/lipid interactions. Nt17 contains multiple sites of potential post-translational modification. Acetylation occurs at lysine 6, 9, and/or 15 while phosphorylation occurs at threonine 3, serine 13, and/or serine 16. Such modifications affect both aggregation and lipid binding through altering intramolecular interactions (i.e. electrostatics, hydrophobic interactions, and salt-bridges) critical to oligomer formation and stability. A mechanistic understanding of how acetylation and phosphorylation impacts oligomeric intermediates, subsequent aggregation, and lipid interactions can provide critical insights into toxic mechanism and elucidate potential therapeutic targets. The role of intramolecular interactions, most notably electrostatics, in htt interactions with respect to aggregation and lipid binding was measured using a combination of thioflavin-T aggregation assays, colorimetric lipid binding assays, atomic force microscopy, and mass spectrometry. Incubation of free Nt17 peptides (without the polyQ domain) containing point mutations with htt-exon1(46Q) most notably influenced aggregation, with the incorporation of free peptides reducing aggregation relative to htt-exon1(46Q) alone. Oligomers were exposed to lipid vesicles, and those with free Nt17 peptide incorporated minimally impacted interactions relative to those exclusively containing htt-exon1(46Q). Collectively, this suggests that while post-translational modifications impact fibril nucleation within oligomers, charge plays a limited role in facilitating the interaction between htt oligomers and lipid membranes.

In silico Analysis of a 29 kDa Echinococcus granulosus Protoscolex Protein (P29) as a Vaccine Candidate against Cystic Echinococcosis.

Vaccination can be a key step in controlling hydatid cyst infection in humans and livestock in endemic areas of the disease. The aim of the Present study was to determine some of the basal biochemical properties followed by prediction and screening of B-cell and MHC-binding epitopes of EgP29 protein in silico. Some of the basic physico-chemical properties along with antigenicity, allergenicity, solubility, post-translational modification (PTM) sites, subcellular localization, signal peptide, transmembrane domain, secondary and tertiary structures followed by refinement and validations were computationally determined for this protein. Also, B-cell epitopes were predicted and screened using various web servers, while MHC-binding and CTL epitopes were predicted using IEDB and NetCTL servers, respectively. The protein is a 238-residue, 27 kDa molecule, with high thermotolerance (aliphatic: 71.81) and hydrophilicity (negative GRAVY). There were several glycosylation and phosphorylation sites in the sequence, without a transmembrane domain and signal peptide. Moreover, several B-cell and MHC-binding epitopes were found in the EgP29 protein, which could be further used in multi-epitope vaccines. In conclusion, results of the present study can be a promising sign for achieving effective approaches to the preparation of a multi-epitope vaccines against echinococcosis. So, it is necessary that the effectiveness of the protein and its epitopes be evaluated in vitro and in vivo.

Strain-specific responsiveness of hepatitis D virus to interferon-alpha treatment

Pegylated interferon alpha (pegIFNα) is commonly used for the treatment of people infected with HDV. However, its mode of action in HDV-infected cells remains elusive and only a minority of people respond to pegIFNα therapy. Herein, we aimed to assess the responsiveness of three different cloned HDV strains to pegIFNα. We used a previously cloned HDV genotype 1 strain (dubbed HDV-1a) that appeared insensitive to interferon-α invitro, a new HDV strain (HDV-1p) we isolated from an individual achieving later sustained response to IFNα therapy, and one phylogenetically distant genotype 3 strain (HDV-3). PegIFNα was administered to human liver chimeric mice infected with HBV and the different HDV strains or to HBV/HDV infected human hepatocytes isolated from chimeric mice. Virological parameters and host responses were analysed by qPCR, sequencing, immunoblotting, RNA in situ hybridisation and immunofluorescence staining. PegIFNα treatment efficiently reduced HDV RNA viraemia (∼2-log) and intrahepatic HDV markers both in mice infected with HBV/HDV-1p and HBV/HDV-3. In contrast, HDV parameters remained unaffected by pegIFNα treatment both in mice (up to 9 weeks) and in isolated cells infected with HBV/HDV-1a. Notably, HBV viraemia was efficiently lowered (∼2-log) and human interferon-stimulated genes similarly induced in all three HBV/HDV-infected mouse groups receiving pegIFNα. Genome sequencing revealed highly conserved ribozyme and L-hepatitis D antigen post-translational modification sites among all three isolates. Our comparative study indicates the ability of pegIFNα to lower HDV loads in stably infected human hepatocytes invivo and the existence of complex virus-specific determinants of IFNα responsiveness. Understanding factors counteracting HDV infections is paramount to develop curative therapies. We compared the responsiveness of three different cloned HDV strains to pegylated interferon alpha in chronically infected mice. The different responsiveness of these HDV isolates to treatment highlights a previously underestimated heterogeneity among HDV strains.

Five Post-Translational Modification Residues of CmPT2 Play Key Roles in Yeast and Rice.

Chrysanthemum (Chrysanthemum morifolium Ramat.) is one of the largest cut flowers in the world. Phosphate transporter Pht1 family member CmPht1;2 protein (CmPT2) plays an important role in response to low-phosphate (LP) stress in chrysanthemum. Post-translational modification (PTM) can modulate the function of proteins in multiple ways. Here, we used yeast and rice systems to study the role of putative PTM in CmPT2 by determining the effect of mutation of key amino acid residues of putative glycosylation, phosphorylation, and myristoylation sites. We chose nine amino acid residues in the putative PTM sites and mutated them to alanine (A) (Cmphts). CmPT2 recovered the growth of yeast strain MB192 under LP conditions. However, G84A, G222A, T239A, Y242A, and N422A mutants could not grow normally under LP conditions. Analysis of phosphorus absorption kinetics showed that the Km of CmPT2 was 65.7 μM. Among the nine Cmphts, the expression of five with larger Km (124.4-397.5 μM) than CmPT2 was further evaluated in rice. Overexpression of CmPT2-OE increased plant height, effective panicle numbers, branch numbers, and yield compared with that of wild type 'Wuyunjing No. 7' (W7). Overexpression of Cmphts-OE led to decreased plant height and effective panicle numbers compared with that of the CmPT2-OE strain. The Pi content in roots of CmPT2-OE was higher than that of the W7 under both high (normal) phosphate (HP) and LP conditions. However, the Pi content in the leaves and roots was significantly lower in the N422A-OE strain than in the CmPT2-OE strain under both HP and LP conditions. Under LP conditions, the phosphorus starvation response (PSR) genes in CmPT2-OE were inhibited at the transcription level. The expression patterns of phosphorus-related genes in T239A, Y242A, and N422A-OE under LP conditions were different from those of CmPT2-OE. In conclusion, these five post-translational modification residues of CmPT2 play key roles in modulating the function of CmPT2. This work boosters our understanding of the function of phosphate transporters and provides genetic resources for improving the efficiency of phosphorus utilization in crop plants.

Insertions and deletions in the hypervariable region of the hepatitis E virus genome in individuals with acute and chronic infection.

Hepatitis E virus is a major cause of acute hepatitis worldwide and can progress to chronicity in immunocompromised individuals. Various virus-host recombination events have been reported in the hypervariable region of the hepatitis E virus genome, but the patterns of assembly and selection remain unclear. To gain further insight into viral evolution, we assessed the presence of low abundance variants in 16 samples from individuals with acute or chronic infection using a targeted next-generation sequencing approach. In seven samples, different variants with insertions and/or deletions were identified. Among them, eight insertions originating either from human genes or from the hepatitis E virus genome. Five different deletions could be identified. The amino acid composition of sequences with insertions showed a higher frequency of lysine and a lower abundance of proline, and additionally acetylation and ubiquitination sites were more frequent than in hepatitis E virus wild-type sequences. These findings suggest that the nucleotide composition of insertions and sites for post-translational modification may contribute to recombination events. Although the impact of low-level hepatitis E virus variants is uncertain, our results highlight the importance of a highly sensitive next-generation sequencing approach to capture the full diversity of hypervariable region.

Potential implications of the glycosylation patterns in collagen α1(I) and α2(I) chains for fibril assembly and growth

O-Glycosylation of hydroxylysine (Hyl) in collagen occurs at an early stage of biosynthesis before the triple-helix has formed. This simple post-translational modification (PTM) of lysine by either a galactosyl or glucosylgalactosyl moiety is highly conserved in collagens and depends on the species, type of tissue and the collagen amino acid sequence. The structural/functional reason why only specific lysines are modified is poorly understood, and has led to increased efforts to map the sites of PTMs on collagen sequences from different species and to ascertain their potential role in vivo. To investigate this, we purified collagen type I (Col1) from the skins of four animals, then used mass spectrometry and proteomic techniques to identify lysines that were oxidised, galactosylated, glucosylgalactosylated, or glycated in its mature sequence. We found 18 out of the 38 lysines in collagen type Iα1, (Col1A1) and 7 of the 30 lysines in collagen type Iα2 (Col1A2) were glycosylated. Six of these modifications had not been reported before, and included a lysine involved in crosslinking collagen molecules. A Fourier transform analysis of the positions of the glycosylated hydroxylysines showed they display a regular axial distribution with the same d-period observed in collagen fibrils. The significance of this finding in terms of the assembly of collagen molecules into fibrils and of potential restrictions on the growth of the collagen fibrils is discussed.

The role of post-translational modifications in synaptic AMPA receptor activity.

AMPA-type receptors for the neurotransmitter glutamate are very dynamic entities, and changes in their synaptic abundance underlie different forms of synaptic plasticity, including long-term synaptic potentiation (LTP), long-term depression (LTD) and homeostatic scaling. The different AMPA receptor subunits (GluA1-GluA4) share a common modular structure and membrane topology, and their intracellular C-terminus tail is responsible for the interaction with intracellular proteins important in receptor trafficking. The latter sequence differs between subunits and contains most sites for post-translational modifications of the receptors, including phosphorylation, O-GlcNAcylation, ubiquitination, acetylation, palmitoylation and nitrosylation, which affect differentially the various subunits. Considering that each single subunit may undergo modifications in multiple sites, and that AMPA receptors may be formed by the assembly of different subunits, this creates multiple layers of regulation of the receptors with impact in synaptic function and plasticity. This review discusses the diversity of mechanisms involved in the post-translational modification of AMPA receptor subunits, and their impact on the subcellular distribution and synaptic activity of the receptors.