Informal carers' experiences in everyday life and the use of digital assistive technology for time management in persons with dementia or mild cognitive impairment

BACKGROUND

Digital assistive technology (DAT) may support time management in people with dementia or mild cognitive impairment (MCI), but research on DAT for time management is limited. We aimed to explore how everyday could be supported by DAT for time management in persons with dementia or MCI from informal carers' perspectives. This study focused on a DAT device for time management called MEMOplanner (MMP).

METHOD

Using a mixed-methods design, we utilized the Time-Proxy© questionnaire and a study-specific interview guide to investigate the perspectives of informal carers (n = 8) regarding the use of MMP by individuals with dementia or MCI.

RESULT

The MMP was helpful in keeping track of time and activity. It helped to maintain an active lifestyle and facilitated communication. However, the MMP did not reduce the need for assistance from the informal carers, and it took time to learn the different functions of the device. Further research into employing a more extensive array of DAT for time management or other areas to assist individuals with dementia will yield valuable insights into enhancing and sustaining a higher quality of life despite cognitive decline.

Phosphorylation of the compartmentalized PKA substrate TAF15 regulates RNA-protein interactions

Spatiotemporal-controlled second messengers alter molecular interactions of central signaling nodes for ensuring physiological signal transmission. One prototypical second messenger molecule which modulates kinase signal transmission is the cyclic-adenosine monophosphate (cAMP). The main proteinogenic cellular effectors of cAMP are compartmentalized protein kinase A (PKA) complexes. Their cell-type specific compositions precisely coordinate substrate phosphorylation and proper signal propagation which is indispensable for numerous cell-type specific functions. Here we present evidence that TAF15, which is implicated in the etiology of amyotrophic lateral sclerosis, represents a novel nuclear PKA substrate. In cross-linking and immunoprecipitation experiments (iCLIP) we showed that TAF15 phosphorylation alters the binding to target transcripts related to mRNA maturation, splicing and protein-binding related functions. TAF15 appears to be one of multiple PKA substrates that undergo RNA-binding dynamics upon phosphorylation. We observed that the activation of the cAMP-PKA signaling axis caused a change in the composition of a collection of RNA species that interact with TAF15. This observation appears to be a broader principle in the regulation of molecular interactions, as we identified a significant enrichment of RNA-binding proteins within endogenous PKA complexes. We assume that phosphorylation of RNA-binding domains adds another layer of regulation to binary protein-RNAs interactions with consequences to RNA features including binding specificities, localization, abundance and composition.

Fonsecaea pedrosoi produces ferricrocin and can utilize different host iron sources

The survival of living organisms depends on iron, one of the most abundant metals in the Earth's crust. Nevertheless, this micronutrient is poorly available in our aerobic atmosphere as well as inside the mammalian host. This problem is circumvented by the expression of high affinity iron uptake machineries, including the production of siderophores, in pathogenic fungi. Here we demonstrated that F. pedrosoi, the causative agent of the neglected tropical disease chromoblastomycosis, presents gene clusters for siderophore production. In addition, ten putative siderophore transporters were identified. Those genes are upregulated under iron starvation, a condition that induces the secretion of hydroxamates, as revealed by chrome azurol S assays. RP-HPLC and mass spectrometry analysis allowed the identification of ferricrocin as an intra- and extracellular siderophore. F. pedrosoi can grow in different iron sources, including the bacterial ferrioxamine B and the host proteins ferritin, hemoglobin and holotransferrin. Of note, addition of hemoglobin, lactoferrin and holotransferrin to the growth medium of macrophages infected with F. pedrosoi enhanced significantly fungal survival. The ability to produce siderophores in iron limited conditions added to the versatility to utilize different sources of iron are strategies that certainly may contribute to fungal survival inside the host.

PKN1 Exerts Neurodegenerative Effects in an In Vitro Model of Cerebellar Hypoxic-Ischemic Encephalopathy via Inhibition of AKT/GSK3β Signaling

We recently identified protein kinase N1 (PKN1) as a negative gatekeeper of neuronal AKT protein kinase activity during postnatal cerebellar development. The developing cerebellum is specifically vulnerable to hypoxia-ischemia (HI), as it occurs during hypoxic-ischemic encephalopathy, a condition typically caused by oxygen deprivation during or shortly after birth. In that context, activation of the AKT cell survival pathway has emerged as a promising new target for neuroprotective interventions. Here, we investigated the role of PKN1 in an in vitro model of HI, using postnatal cerebellar granule cells (Cgc) derived from Pkn1 wildtype and Pkn1-/- mice. Pkn1-/- Cgc showed significantly higher AKT phosphorylation, resulting in reduced caspase-3 activation and improved survival after HI. Pkn1-/- Cgc also showed enhanced axonal outgrowth on growth-inhibitory glial scar substrates, further pointing towards a protective phenotype of Pkn1 knockout after HI. The specific PKN1 phosphorylation site S374 was functionally relevant for the enhanced axonal outgrowth and AKT interaction. Additionally, PKN1pS374 shows a steep decrease during cerebellar development. In summary, we demonstrate the pathological relevance of the PKN1-AKT interaction in an in vitro HI model and establish the relevant PKN1 phosphorylation sites, contributing important information towards the development of specific PKN1 inhibitors.

Iron Starvation Induces Ferricrocin Production and the Reductive Iron Acquisition System in the Chromoblastomycosis Agent Cladophialophora carrionii

Iron is a micronutrient required by almost all living organisms. Despite being essential, the availability of this metal is low in aerobic environments. Additionally, mammalian hosts evolved strategies to restrict iron from invading microorganisms. In this scenario, the survival of pathogenic fungi depends on high-affinity iron uptake mechanisms. Here, we show that the production of siderophores and the reductive iron acquisition system (RIA) are employed by Cladophialophora carrionii under iron restriction. This black fungus is one of the causative agents of chromoblastomycosis, a neglected subcutaneous tropical disease. Siderophore biosynthesis genes are arranged in clusters and, interestingly, two RIA systems are present in the genome. Orthologs of putative siderophore transporters were identified as well. Iron starvation regulates the expression of genes related to both siderophore production and RIA systems, as well as of two transcription factors that regulate iron homeostasis in fungi. A chrome azurol S assay demonstrated the secretion of hydroxamate-type siderophores, which were further identified via RP-HPLC and mass spectrometry as ferricrocin. An analysis of cell extracts also revealed ferricrocin as an intracellular siderophore. The presence of active high-affinity iron acquisition systems may surely contribute to fungal survival during infection.

Protein Networks Associated with Native Metabotropic Glutamate 1 Receptors (mGlu1) in the Mouse Cerebellum

The metabotropic glutamate receptor 1 (mGlu1) plays a pivotal role in synaptic transmission and neuronal plasticity. Despite the fact that several interacting proteins involved in the mGlu1 subcellular trafficking and intracellular transduction mechanisms have been identified, the protein network associated with this receptor in specific brain areas remains largely unknown. To identify novel mGlu1-associated protein complexes in the mouse cerebellum, we used an unbiased tissue-specific proteomic approach, namely co-immunoprecipitation followed by liquid chromatography/tandem mass spectrometry analysis. Many well-known protein complexes as well as novel interactors were identified, including G-proteins, Homer, δ2 glutamate receptor, 14-3-3 proteins, and Na/K-ATPases. A novel putative interactor, KCTD12, was further investigated. Reverse co-immunoprecipitation with anti-KCTD12 antibodies revealed mGlu1 in wild-type but not in KCTD12-knock-out homogenates. Freeze-fracture replica immunogold labeling co-localization experiments showed that KCTD12 and mGlu1 are present in the same nanodomain in Purkinje cell spines, although at a distance that suggests that this interaction is mediated through interposed proteins. Consistently, mGlu1 could not be co-immunoprecipitated with KCTD12 from a recombinant mammalian cell line co-expressing the two proteins. The possibility that this interaction was mediated via GABAB receptors was excluded by showing that mGlu1 and KCTD12 still co-immunoprecipitated from GABAB receptor knock-out tissue. In conclusion, this study identifies tissue-specific mGlu1-associated protein clusters including KCTD12 at Purkinje cell synapses.

Ambient Availability of Amino Acids, Proteins, and Iron Impacts Copper Resistance of Aspergillus fumigatus

The transition metals iron and copper are required by virtually all organisms but are toxic in excess. Acquisition of both metals and resistance to copper excess have previously been shown to be important for virulence of the most common airborne human mold pathogen, Aspergillus fumigatus. Here we demonstrate that the ambient availability of amino acids and proteins increases the copper resistance of A. fumigatus wild type and particularly of the ΔcrpA mutant that lacks export-mediated copper detoxification. The highest-protecting activity was found for L-histidine followed by L-asparagine, L-aspartate, L-serine, L-threonine, and L-tyrosine. Other amino acids and proteins also displayed significant but lower protection. The protecting activity of non-proteinogenic D-histidine, L-histidine-mediated growth inhibition in the absence of high-affinity copper uptake, determination of cellular metal contents, and expression analysis of copper-regulated genes suggested that histidine inhibits low-affinity but not high-affinity copper acquisition by extracellular copper complexation. An increase in the cellular copper content was found to be accompanied by an increase in the iron content, and, in agreement, iron starvation increased copper susceptibility, which underlines the importance of cellular metal balancing. Due to the role of iron and copper in nutritional immunity, these findings are likely to play an important role in the host niche.

Intronic tRNAs of mitochondrial origin regulate constitutive and alternative splicing

BACKGROUND

The presence of nuclear mitochondrial DNA (numtDNA) has been reported within several nuclear genomes. Next to mitochondrial protein-coding genes, numtDNA sequences also encode for mitochondrial tRNA genes. However, the biological roles of numtDNA remain elusive.

RESULTS

Employing in silico analysis, we identify 281 mitochondrial tRNA homologs in the human genome, which we term nimtRNAs (nuclear intronic mitochondrial-derived tRNAs), being contained within introns of 76 nuclear host genes. Despite base changes in nimtRNAs when compared to their mtRNA homologs, a canonical tRNA cloverleaf structure is maintained. To address potential functions of intronic nimtRNAs, we insert them into introns of constitutive and alternative splicing reporters and demonstrate that nimtRNAs promote pre-mRNA splicing, dependent on the number and positioning of nimtRNA genes and splice site recognition efficiency. A mutational analysis reveals that the nimtRNA cloverleaf structure is required for the observed splicing increase. Utilizing a CRISPR/Cas9 approach, we show that a partial deletion of a single endogenous nimtRNALys within intron 28 of the PPFIBP1 gene decreases inclusion of the downstream-located exon 29 of the PPFIBP1 mRNA. By employing a pull-down approach followed by mass spectrometry, a 3'-splice site-associated protein network is identified, including KHDRBS1, which we show directly interacts with nimtRNATyr by an electrophoretic mobility shift assay.

CONCLUSIONS

We propose that nimtRNAs, along with associated protein factors, can act as a novel class of intronic splicing regulatory elements in the human genome by participating in the regulation of splicing.

Complementary α-arrestin-ubiquitin ligase complexes control nutrient transporter endocytosis in response to amino acids

How cells adjust nutrient transport across their membranes is incompletely understood. Previously, we have shown that S. cerevisiae broadly re-configures the nutrient transporters at the plasma membrane in response to amino acid availability, through endocytosis of sugar- and amino acid transporters (AATs) (Müller et al., 2015). A genome-wide screen now revealed that the selective endocytosis of four AATs during starvation required the α-arrestin family protein Art2/Ecm21, an adaptor for the ubiquitin ligase Rsp5, and its induction through the general amino acid control pathway. Art2 uses a basic patch to recognize C-terminal acidic sorting motifs in AATs and thereby instructs Rsp5 to ubiquitinate proximal lysine residues. When amino acids are in excess, Rsp5 instead uses TORC1-activated Art1 to detect N-terminal acidic sorting motifs within the same AATs, which initiates exclusive substrate-induced endocytosis. Thus, amino acid excess or starvation activate complementary α-arrestin-Rsp5-complexes to control selective endocytosis and adapt nutrient acquisition.

RcLS2F - A Novel Fungal Class 1 KDAC Co-repressor Complex in Aspergillus nidulans

The fungal class 1 lysine deacetylase (KDAC) RpdA is a promising target for prevention and treatment of invasive fungal infection. RpdA is essential for survival of the most common air-borne mold pathogen Aspergillus fumigatus and the model organism Aspergillus nidulans. In A. nidulans, RpdA depletion induced production of previously unknown small bioactive substances. As known from yeasts and mammals, class 1 KDACs act as components of multimeric protein complexes, which previously was indicated also for A. nidulans. Composition of these complexes, however, remained obscure. In this study, we used tandem affinity purification to characterize different RpdA complexes and their composition in A. nidulans. In addition to known class 1 KDAC interactors, we identified a novel RpdA complex, which was termed RcLS2F. It contains ScrC, previously described as suppressor of the transcription factor CrzA, as well as the uncharacterized protein FscA. We show that recruitment of FscA depends on ScrC and we provide clear evidence that ΔcrzA suppression by ScrC depletion is due to a lack of transcriptional repression caused by loss of the novel RcLS2F complex. Moreover, RcLS2F is essential for sexual development and engaged in an autoregulatory feed-back loop.

Integrative Transcriptome and Proteome Analysis of the Tube Foot and Adhesive Secretions of the Sea Urchin Paracentrotus lividus

Echinoderms, such as the rock-boring sea urchin Paracentrotus lividus, attach temporarily to surfaces during locomotion using their tube feet. They can attach firmly to any substrate and release from it within seconds through the secretion of unknown molecules. The composition of the adhesive, as well as the releasing secretion, remains largely unknown. This study re-analyzed a differential proteome dataset from Lebesgue et al. by mapping mass spectrometry-derived peptides to a P. lividusde novo transcriptome generated in this study. This resulted in a drastic increase in mapped proteins in comparison to the previous publication. The data were subsequently combined with a differential RNAseq approach to identify potential adhesion candidate genes. A gene expression analysis of 59 transcripts using whole mount in situ hybridization led to the identification of 16 transcripts potentially involved in bioadhesion. In the future these data could be useful for the production of synthetic reversible adhesives for industrial and medical purposes.

Metallomics reveals a persisting impact of cadmium on the evolution of metal-selective snail metallothioneins

The tiny contribution of cadmium (Cd) to the composition of the earth's crust contrasts with its high biological significance. We suggest that in gastropod clades, the protein family of metallothioneins (MTs) has evolved to specifically detoxify Cd.

Distinct pathways for zinc metabolism in the terrestrial slug Arion vulgaris

In most organisms, the concentration of free Zn2+ is controlled by metallothioneins (MTs). In contrast, no significant proportions of Zn2+ are bound to MTs in the slug, Arion vulgaris. Instead, this species possesses cytoplasmic low-molecular-weight Zn2+ (LMW Zn) binding compound that divert these metal ions into pathways uncoupled from MT metabolism. Zn2+ is accumulated in the midgut gland calcium cells of Arion vulgaris, where they associate with a low-molecular-weight ligand with an apparent molecular mass of ~ 2,000 Da. Mass spectrometry of the semi-purified LMW Zn binding compound combining an electrospray ion source with a differential mobility analyser coupled to a time-of-flight mass spectrometer revealed the presence of four Zn2+-containing ion signals, which arise from disintegration of one higher MW complex resulting in an ion-mobility diameter of 1.62 nm and a molecular mass of 837 Da. We expect that the novel Zn2+ ion storage pathway may be shared by many other gastropods, and particularly species that possess Cd-selective MT isoforms or variants with only very low affinity to Zn2+.

Cadmium Pathways in Snails Follow a Complementary Strategy between Metallothionein Detoxification and Auxiliary Inactivation by Phytochelatins

Metal detoxification is crucial for animals to cope with environmental exposure. In snails, a pivotal role in protection against cadmium (Cd) is attributed to metallothioneins (MTs). Some gastropod species express, in a lineage-specific manner, Cd-selective MTs devoted exclusively to the binding and detoxification of this single metal, whereas other species of snails possess non-selective MTs, but still show a high tolerance against Cd. An explanation for this may be that invertebrates and in particular snails may also synthetize phytochelatins (PCs), originally known to be produced by plants, to provide protection against metal or metalloid toxicity. Here we demonstrate that despite the fact that similar mechanisms for Cd inactivation exist in snail species through binding of the metal to MTs, the actual detoxification pathways for this metal may follow different traits in a species-specific manner. In particular, this depends on the detoxification capacity of MTs due to their Cd-selective or non-specific binding features. In the terrestrial slug Arion vulgaris, for example, Cd is solely detoxified by a Cd-selective MT isoform (AvMT1). In contrast, the freshwater snail Biomphalaria glabrata activates an additional pathway for metal inactivation by synthesizing phytochelatins, which compensate for the insufficient capacity of its non-selective MT system to detoxify Cd. We hypothesize that in other snails and invertebrate species, too, an alternative inactivation of the metal by PCs may occur, if their MT system is not Cd-selective enough, or its Cd loading capacity is exhausted.

Repaglinide Silences the FOXO3/Lumican Axis and Represses the Associated Metastatic Potential of Neuronal Cancer Cells

The transcription factor FOXO3 is associated with poor outcome in high-stage neuroblastoma (NB), as it facilitates chemoprotection and tumor angiogenesis. In other tumor entities, FOXO3 stimulates metastasis formation, one of the biggest challenges in the treatment of aggressive NB. However, the impact of FOXO3 on the metastatic potential of neuronal tumor cells remains largely unknown. In the present study, we uncover the small leucine-rich proteoglycan family member lumican (LUM) as a FOXO3-regulated gene that stimulates cellular migration in NB. By a drug-library screen we identified the small molecular weight compound repaglinide (RPG) as a putative FOXO3 inhibitor. Here, we verify that RPG binds to the FOXO3-DNA-binding-domain (DBD) and thereby silences the transcriptional activity of FOXO3. Consistent with the concept that the FOXO3/LUM axis enhances the migratory capacity of aggressive NB cells, we demonstrate that stable knockdown of LUM abrogates the FOXO3-mediated increase in cellular migration. Importantly, FOXO3 inhibition by RPG represses the binding of FOXO3 to the LUM promoter, inhibits FOXO3-mediated LUM RNA and protein expression, and efficiently abrogates FOXO3-triggered cellular “wound healing” as well as spheroid-based 3D-migration. Thus, silencing the FOXO3/LUM axis by the FDA-approved compound RPG represents a promising strategy for novel therapeutic interventions in NB and other FOXO3-dependent tumors.

Phosphorylation of Drosophila CENP-A on serine 20 regulates protein turn-over and centromere-specific loading

Centromeres are specialized chromosomal regions epigenetically defined by the presence of the histone H3 variant CENP-A. CENP-A is required for kinetochore formation which is essential for chromosome segregation during mitosis. Spatial restriction of CENP-A to the centromere is tightly controlled. Its overexpression results in ectopic incorporation and the formation of potentially deleterious neocentromeres in yeast, flies and in various human cancers. While the contribution of posttranslational modifications of CENP-A to these processes has been studied in yeast and mammals to some extent, very little is known about Drosophila melanogaster. Here, we show that CENP-A is phosphorylated at serine 20 (S20) by casein kinase II and that in mitotic cells, the phosphorylated form is enriched on chromatin. Importantly, our results reveal that S20 phosphorylation regulates the turn-over of prenucleosomal CENP-A by the SCFPpa-proteasome pathway and that phosphorylation promotes removal of CENP-A from ectopic but not from centromeric sites in chromatin. We provide multiple lines of evidence for a crucial role of S20 phosphorylation in controlling restricted incorporation of CENP-A into centromeric chromatin in flies. Modulation of the phosphorylation state of S20 may provide the cells with a means to fine-tune CENP-A levels in order to prevent deleterious loading to extra-centromeric sites.

Temporary adhesion of the proseriate flatworm Minona ileanae

Flatworms can very rapidly attach to and detach from many substrates. In the presented work, we analysed the adhesive system of the marine proseriate flatworm Minona ileanae. We used light-, scanning- and transmission electron microscopy to analyse the morphology of the adhesive organs, which are located at the ventral side of the tail-plate. We performed transcriptome sequencing and differential RNA-seq for the identification of tail-specific transcripts. Using in situ hybridization expression screening, we identified nine transcripts that were expressed in the cells of the adhesive organs. Knock-down of five of these transcripts by RNA interference led to a reduction of the animal's attachment capacity. Adhesive proteins in footprints were confirmed using mass spectrometry and antibody staining. Additionally, lectin labelling of footprints revealed the presence of several sugar moieties. Furthermore, we determined a genome size of about 560 Mb for M. ileanae. We demonstrated the potential of Oxford Nanopore sequencing of genomic DNA as a cost-effective tool for identifying the number of repeats within an adhesive protein and for combining transcripts that were fragments of larger genes. A better understanding of the molecules involved in flatworm bioadhesion can pave the way towards developing innovative glues with reversible adhesive properties. This article is part of the theme issue 'Transdisciplinary approaches to the study of adhesion and adhesives in biological systems'.

Endosome and Golgi-associated degradation (EGAD) of membrane proteins regulates sphingolipid metabolism

Cellular homeostasis requires the ubiquitin-dependent degradation of membrane proteins. This was assumed to be mediated exclusively either by endoplasmic reticulum-associated degradation (ERAD) or by endosomal sorting complexes required for transport (ESCRT)-dependent lysosomal degradation. We identified in Saccharomyces cerevisiae an additional pathway that selectively extracts membrane proteins at Golgi and endosomes for degradation by cytosolic proteasomes. One endogenous substrate of this endosome and Golgi-associated degradation pathway (EGAD) is the ER-resident membrane protein Orm2, a negative regulator of sphingolipid biosynthesis. Orm2 degradation is initiated by phosphorylation, which triggers its ER export. Once on Golgi and endosomes, Orm2 is poly-ubiquitinated by the membrane-embedded "Defective in SREBP cleavage" (Dsc) ubiquitin ligase complex. Cdc48/VCP then extracts ubiquitinated Orm2 from membranes, which is tightly coupled to the proteasomal degradation of Orm2. Thereby, EGAD prevents the accumulation of Orm2 at the ER and in post-ER compartments and promotes the controlled de-repression of sphingolipid biosynthesis. Thus, the selective degradation of membrane proteins by EGAD contributes to proteostasis and lipid homeostasis in eukaryotic cells.

Type I and II PRMTs regulate catabolic as well as detoxifying processes in Aspergillus nidulans

In filamentous fungi, arginine methylation has been implicated in morphogenesis, mycotoxin biosynthesis, pathogenicity, and stress response although the exact role of this posttranslational modification in these processes remains obscure. Here, we present the first genome-wide transcriptome analysis in filamentous fungi that compared expression levels of genes regulated by type I and type II protein arginine methyltransferases (PRMTs). In Aspergillus nidulans, three conserved type I and II PRMTs are present that catalyze asymmetric or symmetric dimethylation of arginines. We generated a double type I mutant (ΔrmtA/rmtB) and a combined type I and type II mutant (ΔrmtB/rmtC) to perform genome-wide comparison of their effects on gene expression, but also to monitor putative overlapping activities and reciprocal regulations of type I and type II PRMTs in Aspergillus. Our study demonstrates, that rmtA and rmtC as type I and type II representatives act together as repressors of proteins that are secreted into the extracellular region as the majority of up-regulated genes are mainly involved in catabolic pathways that constitute the secretome of Aspergillus. In addition to a strong up-regulation of secretory genes we found a significant enrichment of down-regulated genes involved in processes related to oxidation-reduction, transmembrane transport and secondary metabolite biosynthesis. Strikingly, nearly 50% of down-regulated genes in both double mutants correspond to redox reaction/oxidoreductase processes, a remarkable finding in light of our recently observed oxidative stress phenotypes of ΔrmtA and ΔrmtC. Finally, analysis of nuclear and cytoplasmic extracts for mono-methylated proteins revealed the presence of both, common and specific substrates of RmtA and RmtC. Thus, our data indicate that type I and II PRMTs in Aspergillus seem to co-regulate the same biological processes but also specifically affect other pathways in a non-redundant fashion.

Rational Design, Synthesis and Preliminary Evaluation of Novel Fusarinine C-Based Chelators for Radiolabeling with Zirconium-89

Fusarinine C (FSC) has recently been shown to be a promising and novel chelator for ⁸⁹Zr. Here, FSC has been further derivatized to optimize the complexation properties of FSC-based chelators for ⁸⁹Zr-labeling by introducing additional carboxylic groups. These were expected to improve the stability of ⁸⁹Zr-complexes by saturating the 8-coordination sphere of [⁸⁹Zr] Zr⁴⁺, and also to introduce functionalities suitable for conjugation to targeting vectors such as monoclonal antibodies. For proof of concept, succinic acid derivatization at the amine groups of FSC was carried out, resulting in FSC(succ)₂ and FSC(succ)₃. FSC(succ)₂ was further derivatized to FSC(succ)₂ AA by reacting with acetic anhydride (AA). The Zr⁴⁺ complexation properties of these chelators were studied by reacting with ZrCl₄. Partition coefficient, protein binding, serum stability, acid dissociation, and transchelation studies of ⁸⁹Zr-complexes were carried out in vitro and the results were compared with those for ⁸⁹Zr-desferrioxamine B ([⁸⁹Zr]Zr-DFO) and ⁸⁹Zr-triacetylfusarinine C ([⁸⁹Zr]Zr-TAFC). The in vivo properties of [⁸⁹Zr]Zr-FSC(succ)₃ were further compared with [⁸⁹Zr]Zr-TAFC in BALB/c mice using micro-positron emission tomography/computer tomography (microPET/CT) imaging. Fusarinine C (succ)₂AA and FSC(succ)₃ were synthesized with satisfactory yields. Complexation with ZrCl₄ was achieved using a simple strategy resulting in high-purity Zr-FSC(succ)₂AA and Zr-FSC(succ)₃ with 1:1 stoichiometry. Distribution coefficients of ⁸⁹Zr-complexes revealed increased hydrophilic character compared to [⁸⁹Zr]Zr-TAFC. All radioligands showed high stability in phosphate buffered saline (PBS) and human serum and low protein-bound activity over a period of seven days. Acid dissociation and transchelation studies exhibited a range of in vitro stabilities following the order: [⁸⁹Zr]Zr-FSC(succ)₃ > [⁸⁹Zr]Zr-TAFC > [⁸⁹Zr]Zr-FSC(succ)₂AA >> [⁸⁹Zr]Zr-DFO. Biodistribution studies of [⁸⁹Zr]Zr-FSC(succ)₃ revealed a slower excretion pattern compared to [⁸⁹Zr]Zr-TAFC. In conclusion, [⁸⁹Zr]Zr-FSC(succ)₃ showed the best stability and inertness. The promising results obtained with [⁸⁹Zr]Zr-FSC(succ)₂AA highlight the potential of FSC(succ)₂ as a monovalent chelator for conjugation to targeted biomolecules, in particular, monoclonal antibodies.

A mechanism for temporary bioadhesion

The flatworm Macrostomum lignano features a duo-gland adhesive system that allows it to repeatedly attach to and release from substrates in seawater within a minute. However, little is known about the molecules involved in this temporary adhesion. In this study, we show that the attachment of M. lignano relies on the secretion of two large adhesive proteins, M. lignano adhesion protein 1 (Mlig-ap1) and Mlig-ap2. We revealed that both proteins are expressed in the adhesive gland cells and that their distribution within the adhesive footprints was spatially restricted. RNA interference knockdown experiments demonstrated the essential function of these two proteins in flatworm adhesion. Negatively charged modified sugars in the surrounding water inhibited flatworm attachment, while positively charged molecules impeded detachment. In addition, we found that M. lignano could not adhere to strongly hydrated surfaces. We propose an attachment-release model where Mlig-ap2 attaches to the substrate and Mlig-ap1 exhibits a cohesive function. A small negatively charged molecule is secreted that interferes with Mlig-ap1, inducing detachment. These findings are of relevance for fundamental adhesion science and efforts to mitigate biofouling. Further, this model of flatworm temporary adhesion may serve as the starting point for the development of synthetic reversible adhesion systems for medicinal and industrial applications.

Triacetylfusarinine C: A urine biomarker for diagnosis of invasive aspergillosis

OBJECTIVES

Early diagnosis of invasive aspergillosis (IA) remains challenging, with available diagnostics being limited by inadequate sensitivities and specificities. Triacetylfusarinine C, a fungal siderophore that has been shown to accumulate in urine in animal models, is a potential new biomarker for diagnosis of IA.

METHODS

We developed a method allowing absolute and matrix-independent mass spectrometric quantification of TAFC. Urine TAFC, normalized to creatinine, was determined in 44 samples from 24 patients with underlying hematologic malignancies and probable, possible or no IA according to current EORTC/MSG criteria and compared to other established biomarkers measured in urine and same-day blood samples.

RESULTS

TAFC/creatinine sensitivity, specificity, positive and negative likelihood ratio for probable versus no IA (cut-off ≥ 3) were 0.86, 0.88, 6.86, 0.16 per patient.

CONCLUSION

For the first time, we provide proof for the occurrence of TAFC in human urine. TAFC/creatinine index determination in urine showed promising results for diagnosis of IA offering the advantages of non-invasive sampling. Sensitivity and specificity were similar as reported for GM determination in serum and bronchoalveolar lavage, the gold standard mycological criterion for IA diagnosis.

Translation of non-standard codon nucleotides reveals minimal requirements for codon-anticodon interactions

The precise interplay between the mRNA codon and the tRNA anticodon is crucial for ensuring efficient and accurate translation by the ribosome. The insertion of RNA nucleobase derivatives in the mRNA allowed us to modulate the stability of the codon-anticodon interaction in the decoding site of bacterial and eukaryotic ribosomes, allowing an in-depth analysis of codon recognition. We found the hydrogen bond between the N1 of purines and the N3 of pyrimidines to be sufficient for decoding of the first two codon nucleotides, whereas adequate stacking between the RNA bases is critical at the wobble position. Inosine, found in eukaryotic mRNAs, is an important example of destabilization of the codon-anticodon interaction. Whereas single inosines are efficiently translated, multiple inosines, e.g., in the serotonin receptor 5-HT2C mRNA, inhibit translation. Thus, our results indicate that despite the robustness of the decoding process, its tolerance toward the weakening of codon-anticodon interactions is limited.

Atomic mutagenesis of stop codon nucleotides reveals the chemical prerequisites for release factor-mediated peptide release

Termination of protein synthesis is triggered by the recognition of a stop codon at the ribosomal A site and is mediated by class I release factors (RFs). Whereas in bacteria, RF1 and RF2 promote termination at UAA/UAG and UAA/UGA stop codons, respectively, eukaryotes only depend on one RF (eRF1) to initiate peptide release at all three stop codons. Based on several structural as well as biochemical studies, interactions between mRNA, tRNA, and rRNA have been proposed to be required for stop codon recognition. In this study, the influence of these interactions was investigated by using chemically modified stop codons. Single functional groups within stop codon nucleotides were substituted to weaken or completely eliminate specific interactions between the respective mRNA and RFs. Our findings provide detailed insight into the recognition mode of bacterial and eukaryotic RFs, thereby revealing the chemical groups of nucleotides that define the identity of stop codons and provide the means to discriminate against noncognate stop codons or UGG sense codons.

Metal binding functions of metallothioneins in the slugArion vulgarisdiffer from metal-specific isoforms of terrestrial snails

Arion vulgarisis a European slug with a huge potential for accumulating and detoxifying heavy metals.

Ergothioneine Biosynthesis and Functionality in the Opportunistic Fungal Pathogen, Aspergillus fumigatus

Ergothioneine (EGT; 2-mercaptohistidine trimethylbetaine) is a trimethylated and sulphurised histidine derivative which exhibits antioxidant properties. Here we report that deletion of Aspergillus fumigatus egtA (AFUA_2G15650), which encodes a trimodular enzyme, abrogated EGT biosynthesis in this opportunistic pathogen. EGT biosynthetic deficiency in A. fumigatus significantly reduced resistance to elevated H₂O₂ and menadione, respectively, impaired gliotoxin production and resulted in attenuated conidiation. Quantitative proteomic analysis revealed substantial proteomic remodelling in ΔegtA compared to wild-type under both basal and ROS conditions, whereby the abundance of 290 proteins was altered. Specifically, the reciprocal differential abundance of cystathionine γ-synthase and β-lyase, respectively, influenced cystathionine availability to effect EGT biosynthesis. A combined deficiency in EGT biosynthesis and the oxidative stress response regulator Yap1, which led to extreme oxidative stress susceptibility, decreased resistance to heavy metals and production of the extracellular siderophore triacetylfusarinine C and increased accumulation of the intracellular siderophore ferricrocin. EGT dissipated H₂O₂ in vitro, and elevated intracellular GSH levels accompanied abrogation of EGT biosynthesis. EGT deficiency only decreased resistance to high H₂O₂ levels which suggests functionality as an auxiliary antioxidant, required for growth at elevated oxidative stress conditions. Combined, these data reveal new interactions between cellular redox homeostasis, secondary metabolism and metal ion homeostasis.

Profiling of adhesive-related genes in the freshwater cnidarian Hydra magnipapillata by transcriptomics and proteomics

The differentiated ectodermal basal disc cells of the freshwater cnidarian Hydra secrete proteinaceous glue to temporarily attach themselves to underwater surfaces. Using transcriptome sequencing and a basal disc-specific RNA-seq combined with in situ hybridisation a highly specific set of candidate adhesive genes was identified. A de novo transcriptome assembly of 55,849 transcripts (>200 bp) was generated using paired-end and single reads from Illumina libraries constructed from different polyp conditions. Differential transcriptomics and spatial gene expression analysis by in situ hybridisation allowed the identification of 40 transcripts exclusively expressed in the ectodermal basal disc cells. Comparisons after mass spectrometry analysis of the adhesive secretion showed a total of 21 transcripts to be basal disc specific and eventually secreted through basal disc cells. This is the first study to survey adhesion-related genes in Hydra. The candidate list presented in this study provides a platform for unravelling the molecular mechanism of underwater adhesion of Hydra.

Novel Insights into the PKCβ-dependent Regulation of the Oxidoreductase p66Shc

Dysfunctional mitochondria contribute to the development of many diseases and pathological conditions through the excessive production of reactive oxygen species (ROS), and, where studied, ablation of p66Shc (p66) was beneficial. p66 translocates to the mitochondria and oxidizes cytochrome c to yield H₂O₂, which in turn initiates cell death. PKCβ-mediated phosphorylation of serine 36 in p66 has been implicated as a key regulatory step preceding mitochondrial translocation, ROS production, and cell death, and PKCβ thus may provide a target for therapeutic intervention. We performed a reassessment of PKCβ regulation of the oxidoreductase activity of p66. Although our experiments did not substantiate Ser³⁶ phosphorylation by PKCβ, they instead provided evidence for Ser¹³⁹ and Ser²¹³ as PKCβ phosphorylation sites regulating the pro-oxidant and pro-apoptotic function of p66. Mutation of another predicted PKCβ phosphorylation site also located in the phosphotyrosine binding domain, threonine 206, had no phenotype. Intriguingly, p66 with Thr²⁰⁶ and Ser²¹³ mutated to glutamic acid showed a gain-of-function phenotype with significantly increased ROS production and cell death induction. Taken together, these data argue for a complex mechanism of PKCβ-dependent regulation of p66 activation involving Ser¹³⁹ and a motif surrounding Ser²¹³.

Caspases uncouple p27(Kip1) from cell cycle regulated degradation and abolish its ability to stimulate cell migration and invasion

In addition to their role in programmed cell death, caspases exert non-lethal functions in diverse developmental processes including cell differentiation or tissue remodeling. Terminal cell cycle exit and differentiation can be promoted by increased level of the CDK inhibitor p27^Kip1. Activated caspases cause proteolytic processing of p27, and we identified a novel caspase cleavage site in human p27 that removes a C-terminal fragment of 22 amino acids from the CDK inhibitor, including a phosphodegron. Thereby, caspases protect the inhibitor from SCF-Skp2-mediated degradation in S, G2 and M phases of the cell cycle. As a consequence, p27 becomes stabilized and remains an efficient nuclear inhibitor of cell cycle progression. Besides controlling cyclin/CDK kinase activity, p27 also regulates cytoskeletal dynamics, cell motility and cell invasion. Following processing by caspases, p27 fails to bind to RhoA and to inhibit its activation, and thereby abolishes the ability of p27 to stimulate cell migration and invasion. We propose that the stabilization of the CDK inhibitor and elimination of RhoA-induced cytoskeletal remodeling upon caspase processing could contribute to cell cycle exit and cytoskeletal remodeling during non-lethal caspase controlled differentiation processes.

A novel role for the histone acetyltransferase Hat1 in the CENP-A/CID assembly pathway in Drosophila melanogaster

The incorporation of CENP-A into centromeric chromatin is an essential prerequisite for kinetochore formation. Yet, the molecular mechanisms governing this process are surprisingly divergent in different organisms. While CENP-A loading mechanisms have been studied in some detail in mammals, there are still large gaps to our understanding of CENP-A/Cid loading pathways in Drosophila. Here, we report on the characterization and delineation of at least three different CENP-A preloading complexes in Drosophila. Two complexes contain the CENP-A chaperones CAL1, FACT and/or Caf1/Rbap48. Notably, we identified a novel complex consisting of the histone acetyltransferase Hat1, Caf1 and CENP-A/H4. We show that Hat1 is required for proper CENP-A loading into chromatin, since knock-down in S2 cells leads to reduced incorporation of newly synthesized CENP-A. In addition, we demonstrate that CENP-A/Cid interacts with the HAT1 complex via an N-terminal region, which is acetylated in cytoplasmic but not in nuclear CENP-A. Since Hat1 is not responsible for acetylation of CENP-A/Cid, these results suggest a histone acetyltransferase activity-independent escort function for Hat1. Thus, our results point toward intriguing analogies between the complex processing pathways of newly synthesized CENP-A and canonical histones.

Phospholipid Binding Protein C Inhibitor (PCI) Is Present on Microparticles Generated In Vitro and In Vivo

Protein C inhibitor is a secreted, non-specific serine protease inhibitor with broad protease reactivity. It binds glycosaminoglycans and anionic phospholipids, which can modulate its activity. Anionic phospholipids, such as phosphatidylserine are normally localized to the inner leaflet of the plasma membrane, but are exposed on activated and apoptotic cells and on plasma membrane-derived microparticles. In this report we show by flow cytometry that microparticles derived from cultured cells and activated platelets incorporated protein C inhibitor during membrane blebbing. Moreover, protein C inhibitor is present in/on microparticles circulating in normal human plasma as judged from Western blots, ELISAs, flow cytometry, and mass spectrometry. These plasma microparticles are mainly derived from megakaryocytes. They seem to be saturated with protein C inhibitor, since they do not bind added fluorescence-labeled protein C inhibitor. Heparin partially removed microparticle-bound protein C inhibitor, supporting our assumption that protein C inhibitor is bound via phospholipids. To assess the biological role of microparticle-bound protein C inhibitor we performed protease inhibition assays and co-precipitated putative binding partners on microparticles with anti-protein C inhibitor IgG. As judged from amidolytic assays microparticle-bound protein C inhibitor did not inhibit activated protein C or thrombin, nor did microparticles modulate the activity of exogenous protein C inhibitor. Among the proteins co-precipitating with protein C inhibitor, complement factors, especially complement factor 3, were most striking. Taken together, our data do not support a major role of microparticle-associated protein C inhibitor in coagulation, but rather suggest an interaction with proteins of the complement system present on these phospholipid vesicles.

Nucleotide modifications within bacterial messenger RNAs regulate their translation and are able to rewire the genetic code

Nucleotide modifications within RNA transcripts are found in every organism in all three domains of life. 6-methyladeonsine (m⁶A), 5-methylcytosine (m⁵C) and pseudouridine (Ψ) are highly abundant nucleotide modifications in coding sequences of eukaryal mRNAs, while m⁵C and m⁶A modifications have also been discovered in archaeal and bacterial mRNAs. Employing in vitro translation assays, we systematically investigated the influence of nucleotide modifications on translation. We introduced m⁵C, m⁶A, Ψ or 2′-O-methylated nucleotides at each of the three positions within a codon of the bacterial ErmCL mRNA and analyzed their influence on translation. Depending on the respective nucleotide modification, as well as its position within a codon, protein synthesis remained either unaffected or was prematurely terminated at the modification site, resulting in reduced amounts of the full-length peptide. In the latter case, toeprint analysis of ribosomal complexes was consistent with stalling of translation at the modified codon. When multiple nucleotide modifications were introduced within one codon, an additive inhibitory effect on translation was observed. We also identified the m⁵C modification to alter the amino acid identity of the corresponding codon, when positioned at the second codon position. Our results suggest a novel mode of gene regulation by nucleotide modifications in bacterial mRNAs.

The coordinated action of the MVB pathway and autophagy ensures cell survival during starvation

The degradation and recycling of cellular components is essential for cell growth and survival. Here we show how selective and non-selective lysosomal protein degradation pathways cooperate to ensure cell survival upon nutrient limitation. A quantitative analysis of starvation-induced proteome remodeling in yeast reveals comprehensive changes already in the first three hours. In this period, many different integral plasma membrane proteins undergo endocytosis and degradation in vacuoles via the multivesicular body (MVB) pathway. Their degradation becomes essential to maintain critical amino acids levels that uphold protein synthesis early during starvation. This promotes cellular adaptation, including the de novo synthesis of vacuolar hydrolases to boost the vacuolar catabolic activity. This order of events primes vacuoles for the efficient degradation of bulk cytoplasm via autophagy. Hence, a catabolic cascade including the coordinated action of the MVB pathway and autophagy is essential to enter quiescence to survive extended periods of nutrient limitation.

DOI:http://dx.doi.org/10.7554/eLife.07736.001

Yeast and other organisms have evolved to survive extended periods of starvation by digesting their own proteins and other cell materials and thereby recycle them into new proteins and structures. One way in which these cell materials can be destroyed is by a process called autophagy. A membrane forms around the cell material to isolate it from the rest of the cell. In yeast, the resulting structure fuses with a cell compartment called the vacuole, which contains enzymes that break down the cargo into smaller molecules that can be re-used by the cell.

When cells experience starvation, autophagy is not very selective in what it destroys and so it is tightly controlled to avoid damaging important structures in healthy cells. Alongside autophagy, specific proteins in the membrane surrounding a yeast cell can be targeted for destruction by another process called the MVB pathway. Certain membrane proteins are tagged with a small protein called ubiquitin, which leads them to being selectively incorporated into cell compartments called MVBs that then go on to fuse with the vacuole. However, it is not clear how the MVB pathway and autophagy may cooperate to enable the cell to survive periods of starvation.

Here, Müller et al. monitored the changes in the proteins present in yeast cells during a period of starvation. The experiments show that many different membrane proteins in the yeast cells were destroyed via the MVB pathway within three hours of the removal of their food source. This was essential to allow the cells to carry on producing new proteins at this early stage in starvation. These new proteins included the enzymes found in vacuoles, which increased the ability of the cells to break down the proteins and other cell materials that were transported there via autophagy.

These findings show how the MVB pathway and autophagy are co-ordinated to allow cells to survive periods of starvation. The next challenge is to work out how the MVB pathway is regulated at the molecular level in response to fluctuations in nutrient availability.

DOI:http://dx.doi.org/10.7554/eLife.07736.002

Linker histone partial phosphorylation: effects on secondary structure and chromatin condensation

Linker histones are involved in chromatin higher-order structure and gene regulation. We have successfully achieved partial phosphorylation of linker histones in chicken erythrocyte soluble chromatin with CDK2, as indicated by HPCE, MALDI-TOF and Tandem MS. We have studied the effects of linker histone partial phosphorylation on secondary structure and chromatin condensation. Infrared spectroscopy analysis showed a gradual increase of β-structure in the phosphorylated samples, concomitant to a decrease in α-helix/turns, with increasing linker histone phosphorylation. This conformational change could act as the first step in the phosphorylation-induced effects on chromatin condensation. A decrease of the sedimentation rate through sucrose gradients of the phosphorylated samples was observed, indicating a global relaxation of the 30-nm fiber following linker histone phosphorylation. Analysis of specific genes, combining nuclease digestion and qPCR, showed that phosphorylated samples were more accessible than unphosphorylated samples, suggesting local chromatin relaxation. Chromatin aggregation was induced by MgCl₂ and analyzed by dynamic light scattering (DLS). Phosphorylated chromatin had lower percentages in volume of aggregated molecules and the aggregates had smaller hydrodynamic diameter than unphosphorylated chromatin, indicating that linker histone phosphorylation impaired chromatin aggregation. These findings provide new insights into the effects of linker histone phosphorylation in chromatin condensation.

Sequence conservation of linker histones between chicken and mammalian species

The percent identity matrices of two sequence multiple alignments between linker histones from chicken and mammalian species are described. Linker histone protein sequences for chicken, mouse, rat and humans, available on public databases were used. This information is related to the research article entitled "Identification of novel post-translational modifications in linker histones from chicken erythrocytes"published in the Journal of Proteomics [1].

Identification of novel post-translational modifications in linker histones from chicken erythrocytes

Chicken erythrocyte nuclei were digested with micrococcal nuclease and fractionated by centrifugation in low-salt buffer into soluble and insoluble fractions. Post-translational modifications of the purified linker histones of both fractions were analyzed by LC-ESI-MS/MS. All six histone H1 subtypes (H1.01, H1.02, H1.03, H1.10, H1.1L and H1.1R) and histone H5 were identified. Mass spectrometry analysis enabled the identification of a wide range of PTMs, including N(α)-terminal acetylation, acetylation, formylation, phosphorylation and oxidation. A total of nine new modifications in chicken linker histones were mapped, most of them located in the N-terminal and globular domains. Relative quantification of the modified peptides showed that linker histone PTMs were differentially distributed among both chromatin fractions, suggesting their relevance in the regulation of chromatin structure. The analysis of our results combined with previously reported data for chicken and some mammalian species showed that most of the modified positions were conserved throughout evolution, highlighting their importance in specific linker histone functions and epigenetics.

BIOLOGICAL SIGNIFICANCE

Post-translational modifications of linker histones could have a role in the regulation of gene expression through the modulation of chromatin higher-order structure and chromatin remodeling. Finding new PTMs in linker histones is the first step to elucidate their role in the histone code. In this manuscript we report nine new post-translational modifications of the linker histones from chicken erythrocytes, one in H5 and eight in the H1 subtypes. Chromatin fractionated by centrifugation in low-salt buffer resulted in two fractions with different contents and compositions of linker histones and enriched in specific core histone PTMs. Of particular interest is the fact that linker histone PTMs were differentially distributed in both chromatin fractions, suggesting specific functions. Future studies are needed to establish the interplay between PTMs of linker and core histones in order to fully understand chromatin regulation. A protein sequence alignment summarizing the PTMs found to date in chicken, mouse, rat and humans showed that, while many of the modified positions were conserved between these species, the type of modification often varied depending on the species or the cellular type. This finding suggests an important role for the PTMs in the regulation of linker histone functions.

Novel antibodies directed against the human erythropoietin receptor: creating a basis for clinical implementation

Recombinant human erythropoietin (rHuEPO) is an effective treatment for anaemia but concerns that it causes disease progression in cancer patients by activation of EPO receptors (EPOR) in tumour tissue have been controversial and have restricted its clinical use. Initial clinical studies were flawed because they used polyclonal antibodies, later shown to lack specificity for EPOR. Moreover, multiple isoforms of EPOR caused by differential splicing have been reported in cancer cell lines at the mRNA level but investigations of these variants and their potential impact on tumour progression, have been hampered by lack of suitable antibodies. The EpoCan consortium seeks to promote improved pathological testing of EPOR, leading to safer clinical use of rHuEPO, by producing well characterized EPOR antibodies. Using novel genetic and traditional peptide immunization protocols, we have produced mouse and rat monoclonal antibodies, and show that several of these specifically recognize EPOR by Western blot, immunoprecipitation, immunofluorescence, flow cytometry and immunohistochemistry in cell lines and clinical material. Widespread availability of these antibodies should enable the research community to gain a better understanding of the role of EPOR in cancer, and eventually to distinguish patients who can be treated safely by rHuEPO from those at increased risk from treatment.

Hydroxamate production as a high affinity iron acquisition mechanism in Paracoccidioides spp

Iron is a micronutrient required by almost all living organisms, including fungi. Although this metal is abundant, its bioavailability is low either in aerobic environments or within mammalian hosts. As a consequence, pathogenic microorganisms evolved high affinity iron acquisition mechanisms which include the production and uptake of siderophores. Here we investigated the utilization of these molecules by species of the Paracoccidioides genus, the causative agents of a systemic mycosis. It was demonstrated that iron starvation induces the expression of Paracoccidioides ortholog genes for siderophore biosynthesis and transport. Reversed-phase HPLC analysis revealed that the fungus produces and secretes coprogen B, which generates dimerumic acid as a breakdown product. Ferricrocin and ferrichrome C were detected in Paracoccidioides as the intracellular produced siderophores. Moreover, the fungus is also able to grow in presence of siderophores as the only iron sources, demonstrating that beyond producing, Paracoccidioides is also able to utilize siderophores for growth, including the xenosiderophore ferrioxamine. Exposure to exogenous ferrioxamine and dimerumic acid increased fungus survival during co-cultivation with macrophages indicating that these molecules play a role during host-pathogen interaction. Furthermore, cross-feeding experiments revealed that Paracoccidioides siderophores promotes growth of Aspergillus nidulans strain unable to produce these iron chelators. Together, these data denote that synthesis and utilization of siderophores is a mechanism used by Paracoccidioides to surpass iron limitation. As iron paucity is found within the host, siderophore production may be related to fungus pathogenicity.

Coordinated binding of Vps4 to ESCRT-III drives membrane neck constriction during MVB vesicle formation

Five endosomal sorting complexes required for transport (ESCRTs) mediate the degradation of ubiquitinated membrane proteins via multivesicular bodies (MVBs) in lysosomes. ESCRT-0, -I, and -II interact with cargo on endosomes. ESCRT-II also initiates the assembly of a ringlike ESCRT-III filament consisting of Vps20, Snf7, Vps24, and Vps2. The AAA-adenosine triphosphatase Vps4 disassembles and recycles the ESCRT-III complex, thereby terminating the ESCRT pathway. A mechanistic role for Vps4 in intraluminal vesicle (ILV) formation has been unclear. By combining yeast genetics, biochemistry, and electron tomography, we find that ESCRT-III assembly on endosomes is required to induce or stabilize the necks of growing MVB ILVs. Yet, ESCRT-III alone is not sufficient to complete ILV biogenesis. Rather, binding of Vps4 to ESCRT-III, coordinated by interactions with Vps2 and Snf7, is coupled to membrane neck constriction during ILV formation. Thus, Vps4 not only recycles ESCRT-III subunits but also cooperates with ESCRT-III to drive distinct membrane-remodeling steps, which lead to efficient membrane scission at the end of ILV biogenesis in vivo.

Identification of voltage-gated K(+) channel beta 2 (Kvβ2) subunit as a novel interaction partner of the pain transducer Transient Receptor Potential Vanilloid 1 channel (TRPV1)

The Transient Receptor Potential Vanilloid 1 (TRPV1, vanilloid receptor 1) ion channel plays a key role in the perception of thermal and inflammatory pain, however, its molecular environment in dorsal root ganglia (DRG) is largely unexplored. Utilizing a panel of sequence-directed antibodies against TRPV1 protein and mouse DRG membranes, the channel complex from mouse DRG was detergent-solubilized, isolated by immunoprecipitation and subsequently analyzed by mass spectrometry. A number of potential TRPV1 interaction partners were identified, among them cytoskeletal proteins, signal transduction molecules, and established ion channel subunits. Based on stringent specificity criteria, the voltage-gated K(+) channel beta 2 subunit (Kvβ2), an accessory subunit of voltage-gated K(+) channels, was identified of being associated with native TRPV1 channels. Reverse co-immunoprecipitation and antibody co-staining experiments confirmed TRPV1/Kvβ2 association. Biotinylation assays in the presence of Kvβ2 demonstrated increased cell surface expression levels of TRPV1, while patch-clamp experiments resulted in a significant increase of TRPV1 sensitivity to capsaicin. Our work shows, for the first time, the association of a Kvβ subunit with TRPV1 channels, and suggests that such interaction may play a role in TRPV1 channel trafficking to the plasma membrane.

Characterization of the Link between Ornithine, Arginine, Polyamine and Siderophore Metabolism in Aspergillus fumigatus

The opportunistic fungal pathogen Aspergillus fumigatus produces siderophores for uptake and storage of iron, which is essential for its virulence. The main precursor of siderophore biosynthesis (SB), ornithine, can be produced from glutamate in the mitochondria or by cytosolic hydrolysis of ornithine-derived arginine. Here, we studied the impact of mitochondrial versus cytosolic ornithine biosynthesis on SB by comparison of the arginine auxotrophic mutants ΔargEF and ΔargB, which lack and possess mitochondrial ornithine production, respectively. Deficiency in argEF (encoding acetylglutamate kinase and acetylglutamyl-phosphate-reductase), but not argB (encoding ornithine transcarbamoyl transferase) decreased (i) the cellular ornithine content, (ii) extra- and intracellular SB, (iii) growth under harsh iron starvation, (iv) resistance to the ornithine decarboxylase inhibitor eflornithine, and (v) virulence in the Galleria mellonella larvae model. These lines of evidence indicate that SB is mainly fueled by mitochondrial rather than cytosolic ornithine production and underline the role of SB in virulence. Ornithine content and SB of ΔargB increased with declining arginine supplementation indicating feedback-inhibition of mitochondrial ornithine biosynthesis by arginine. In contrast to SB, the arginine and polyamine contents were only mildly affected in ΔargEF, indicating prioritization of the latter two ornithine-consuming pathways over SB. These data highlight the metabolic differences between the two arginine auxotrophic mutants ΔargEF and ΔargB and demonstrate that supplementation of an auxotrophic mutant does not restore the wild type metabolism at the molecular level, a fact to be considered when working with auxotrophic mutants. Moreover, cross pathway control-mediating CpcA was found to influence the ornithine pool as well as biosynthesis of siderophores and polyamines.

Stability of the endosomal scaffold protein LAMTOR3 depends on heterodimer assembly and proteasomal degradation

LAMTOR3 (MP1) and LAMTOR2 (p14) form a heterodimer as part of the larger Ragulator complex that is required for MAPK and mTOR1 signaling from late endosomes/lysosomes. Here, we show that loss of LAMTOR2 (p14) results in an unstable cytosolic monomeric pool of LAMTOR3 (MP1). Monomeric cytoplasmic LAMTOR3 is rapidly degraded in a proteasome-dependent but lysosome-independent manner. Mutational analyses indicated that the turnover of the protein is dependent on ubiquitination of several lysine residues. Similarly, other Ragulator subunits, LAMTOR1 (p18), LAMTOR4 (c7orf59), and LAMTOR5 (HBXIP), are degraded as well upon the loss of LAMTOR2. Thus the assembly of the Ragulator complex is monitored by cellular quality control systems, most likely to prevent aberrant signaling at the convergence of mTOR and MAPK caused by a defective Ragulator complex.

N-chlorotaurine, a long-lived oxidant produced by human leukocytes, inactivates Shiga toxin of enterohemorrhagic Escherichia coli

N-chlorotaurine (NCT), the main representative of long-lived oxidants produced by granulocytes and monocytes, is known to exert broad-spectrum microbicidal activity. Here we show that NCT directly inactivates Shiga toxin 2 (Stx2), used as a model toxin secreted by enterohemorrhagic Escherichia coli (EHEC). Bacterial growth and Stx2 production were both inhibited by 2 mM NCT. The cytotoxic effect of Stx2 on Vero cells was removed by ≥5.5 mM NCT. Confocal microscopy and FACS analyses showed that the binding of Stx2 to human kidney glomerular endothelial cells was inhibited, and no NCT-treated Stx2 entered the cytosol. Mass spectrometry displayed oxidation of thio groups and aromatic amino acids of Stx2 by NCT. Therefore, long-lived oxidants may act as powerful tools of innate immunity against soluble virulence factors of pathogens. Moreover, inactivation of virulence factors may contribute to therapeutic success of NCT and novel analogs, which are in development as topical antiinfectives.