N-ethylmaleimide sensitive factor (NSF) structure and function

Spectroscopic Methods for Detecting Conformational Changes During Sec18-Lipid Interactions

Vacuole fusion is driven by SNARE proteins that require activation-or priming-by the AAA+ protein Sec18 (NSF) before they can bring membranes together and trigger the merger of two bilayers into a continuous membrane. Sec18 resides on vacuoles prior to engaging inactive cis-SNARE complexes through its interaction with the regulatory lipid phosphatidic acid (PA). Binding PA causes Sec18 to undergo large conformational changes that keeps it bound to the membrane, thus precluding its interactions with SNAREs. Such conformational changes can be measured by various biochemical and biophysical assays. The conversion of PA to diacylglycerol by the PA phosphatase Pah1 releases Sec18 from the membrane-bound pool and promotes its transfer to SNARE complexes allowing priming to occur. Here we describe four spectroscopy-based methods to distinguish conformational changes from alterations in secondary structure during PA binding. These methods only require purified protein and short chain soluble lipids, making the methods rapid and affordable ways to screen the effects of specific protein-lipid interactions. The assays described in this chapter include 1-anilino-8-naphthalenesulfonate (ANS) spectroscopy and intrinsic tryptophan fluorescence to detect exposure of hydrophobic regions; differential scanning fluorometry to measure changes in protein stability across a temperature gradient; and circular dichroism to examine changes in secondary structure.

The role of synaptic protein NSF in the development and progression of neurological diseases

This document provides a comprehensive examination of the pivotal function of the N-ethylmaleimide-sensitive factor (NSF) protein in synaptic function. The NSF protein directly participates in critical biological processes, including the cyclic movement of synaptic vesicles (SVs) between exocytosis and endocytosis, the release and transmission of neurotransmitters, and the development of synaptic plasticity through interactions with various proteins, such as SNARE proteins and neurotransmitter receptors. This review also described the multiple functions of NSF in intracellular membrane fusion events and its close associations with several neurological disorders, such as Parkinson's disease, Alzheimer's disease, and epilepsy. Subsequent studies should concentrate on determining high-resolution structures of NSF in different domains, identifying its specific alterations in various diseases, and screening small molecule regulators of NSF from multiple perspectives. These research endeavors aim to reveal new therapeutic targets associated with the biological functions of NSF and disease mechanisms.

Protection of the Vascular System by Polyethylene Glycol Reduces Secondary Injury Following Spinal Cord Injury in Rats

BACKGROUND

Polyethylene glycol (PEG) is a hydrophilic polymer, which has been known to have a neuroprotective effect by sealing the ruptured cell membrane, but PEG effects on the vascular systems and its underlying mechanisms remain unclear. Here, we showed the neuroprotective effect of PEG by preventing damage to the vascular system.

METHODS

A spinal contusion was made at the T11 segment in male Sprague-Dawley rats. PEG was injected into the subdural space immediately after SCI. Vascular permeability was assessed for 24 h after SCI using intraperitoneally injected Evans blue dye. Junctional complexes were stained with CD31 and ZO-1. Infarct size was analyzed using triphenyltetrazolium chloride, and blood vessels were counted in the epicenter. Behavioral tests for motor and sensory function were performed for 6 weeks. And then the tissue-sparing area was assessed.

RESULTS

Immediately applied PEG significantly reduced the vascular permeability at 6, 12, and 24 h after SCI when it compared to saline, and infarct size was also reduced at 0, 6, and 24 h after SCI. In addition, a great number of blood vessels were observed in PEG group at 6 and 24 h after SCI compared to those of the saline group. The PEG group also showed a significant improvement in motor function. And tissue-sparing areas in the PEG were greater than those of the saline group.

CONCLUSION

The present results provide preclinical evidence for the neuroprotective effects of PEG as a promising therapeutic agent for reducing secondary injury following SCI through vascular protection.

Expression Analysis of Genes Involved in Transport Processes in Mice with MPTP-Induced Model of Parkinson’s Disease

Processes of intracellular and extracellular transport play one of the most important roles in the functioning of cells. Changes to transport mechanisms in a neuron can lead to the disruption of many cellular processes and even to cell death. It was shown that disruption of the processes of vesicular, axonal, and synaptic transport can lead to a number of diseases of the central nervous system, including Parkinson’s disease (PD). Here, we studied changes in the expression of genes whose protein products are involved in the transport processes (Snca, Drd2, Rab5a, Anxa2, and Nsf) in the brain tissues and peripheral blood of mice with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced models of PD. We detected changes in the expressions of Drd2, Anxa2, and Nsf at the earliest modeling stages. Additionally, we have identified conspicuous changes in the expression level of Anxa2 in the striatum and substantia nigra of mice with MPTP-induced models of PD in its early stages. These data clearly suggest the involvement of protein products in these genes in the earliest stages of the pathogenesis of PD.

SNAREs-SAP: SNARE Proteins Identification With PSSM Profiles

Soluble N-ethylmaleimide sensitive factor activating protein receptor (SNARE) proteins are a large family of transmembrane proteins located in organelles and vesicles. The important roles of SNARE proteins include initiating the vesicle fusion process and activating and fusing proteins as they undergo exocytosis activity, and SNARE proteins are also vital for the transport regulation of membrane proteins and non-regulatory vesicles. Therefore, there is great significance in establishing a method to efficiently identify SNARE proteins. However, the identification accuracy of the existing methods such as SNARE CNN is not satisfied. In our study, we developed a method based on a support vector machine (SVM) that can effectively recognize SNARE proteins. We used the position-specific scoring matrix (PSSM) method to extract features of SNARE protein sequences, used the support vector machine recursive elimination correlation bias reduction (SVM-RFE-CBR) algorithm to rank the importance of features, and then screened out the optimal subset of feature data based on the sorted results. We input the feature data into the model when building the model, used 10-fold crossing validation for training, and tested model performance by using an independent dataset. In independent tests, the ability of our method to identify SNARE proteins achieved a sensitivity of 68%, specificity of 94%, accuracy of 92%, area under the curve (AUC) of 84%, and Matthew’s correlation coefficient (MCC) of 0.48. The results of the experiment show that the common evaluation indicators of our method are excellent, indicating that our method performs better than other existing classification methods in identifying SNARE proteins.

LRRK2 G2019S kinase activity triggers neurotoxic NSF aggregation

Parkinson's disease is characterized by the progressive degeneration of dopaminergic neurons within the substantia nigra pars compacta and the presence of protein aggregates in surviving neurons. The LRRK2 G2019S mutation is one of the major determinants of familial Parkinson's disease cases and leads to late-onset Parkinson's disease with pleomorphic pathology, including α-synuclein accumulation and deposition of protein inclusions. We demonstrated that LRRK2 phosphorylates N-ethylmaleimide sensitive factor (NSF). We observed aggregates containing NSF in basal ganglia specimens from patients with Parkinson's disease carrying the G2019S variant, and in cellular and animal models expressing the LRRK2 G2019S variant. We found that LRRK2 G2019S kinase activity induces the accumulation of NSF in toxic aggregates. Of note, the induction of autophagy cleared NSF aggregation and rescued motor and cognitive impairment observed in aged hG2019S bacterial artificial chromosome (BAC) mice. We suggest that LRRK2 G2019S pathological phosphorylation impacts on NSF biochemical properties, thus causing the formation of cytotoxic protein inclusions.

RNA-binding protein FXR1 is presented in rat brain in amyloid form

Amyloids are β-sheets-rich protein fibrils that cause neurodegenerative and other incurable human diseases affecting millions of people worldwide. However, a number of proteins is functional in the amyloid state in various organisms from bacteria to humans. Using an original proteomic approach, we identified a set of proteins forming amyloid-like aggregates in the brain of young healthy rats. One of them is the FXR1 protein, which is known to regulate memory and emotions. We showed that FXR1 clearly colocalizes in cortical neurons with amyloid-specific dyes Congo-Red, Thioflavines S and T. FXR1 extracted from brain by immunoprecipitation shows yellow-green birefringence after staining with Congo red. This protein forms in brain detergent-resistant amyloid oligomers and insoluble aggregates. RNA molecules that are colocalized with FXR1 in cortical neurons are insensitive to treatment with RNase A. All these data suggest that FXR1 functions in rat brain in amyloid form. The N-terminal amyloid-forming fragment of FXR1 is highly conserved across mammals. We assume that the FXR1 protein may be presented in amyloid form in brain of different species of mammals, including humans.

A small-molecule competitive inhibitor of phosphatidic acid binding by the AAA+ protein NSF/Sec18 blocks the SNARE-priming stage of vacuole fusion

The homeostasis of most organelles requires membrane fusion mediated by soluble N -ethylmaleimide-sensitive factor (NSF) attachment protein receptors (SNAREs). SNAREs undergo cycles of activation and deactivation as membranes move through the fusion cycle. At the top of the cycle, inactive cis-SNARE complexes on a single membrane are activated, or primed, by the hexameric ATPase associated with the diverse cellular activities (AAA+) protein, N-ethylmaleimide-sensitive factor (NSF/Sec18), and its co-chaperone α-SNAP/Sec17. Sec18-mediated ATP hydrolysis drives the mechanical disassembly of SNAREs into individual coils, permitting a new cycle of fusion. Previously, we found that Sec18 monomers are sequestered away from SNAREs by binding phosphatidic acid (PA). Sec18 is released from the membrane when PA is hydrolyzed to diacylglycerol by the PA phosphatase Pah1. Although PA can inhibit SNARE priming, it binds other proteins and thus cannot be used as a specific tool to further probe Sec18 activity. Here, we report the discovery of a small-molecule compound, we call IPA (inhibitor of priming activity), that binds Sec18 with high affinity and blocks SNARE activation. We observed that IPA blocks SNARE priming and competes for PA binding to Sec18. Molecular dynamics simulations revealed that IPA induces a more rigid NSF/Sec18 conformation, which potentially disables the flexibility required for Sec18 to bind to PA or to activate SNAREs. We also show that IPA more potently and specifically inhibits NSF/Sec18 activity than does N-ethylmaleimide, requiring the administration of only low micromolar concentrations of IPA, demonstrating that this compound could help to further elucidate SNARE-priming dynamics.

Initial findings of striatum tripartite model in OCD brain samples based on transcriptome analysis

Obsessive-compulsive disorder (OCD) is a psychiatric disorder characterized by obsessions and/or compulsions. Different striatal subregions belonging to the cortico-striato-thalamic circuitry (CSTC) play an important role in the pathophysiology of OCD. The transcriptomes of 3 separate striatal areas (putamen (PT), caudate nucleus (CN) and accumbens nucleus (NAC)) from postmortem brain tissue were compared between 6 OCD and 8 control cases. In addition to network connectivity deregulation, different biological processes are specific to each striatum region according to the tripartite model of the striatum and contribute in various ways to OCD pathophysiology. Specifically, regulation of neurotransmitter levels and presynaptic processes involved in chemical synaptic transmission were shared between NAC and PT. The Gene Ontology terms cellular response to chemical stimulus, response to external stimulus, response to organic substance, regulation of synaptic plasticity, and modulation of synaptic transmission were shared between CN and PT. Most genes harboring common and/or rare variants previously associated with OCD that were differentially expressed or part of a least preserved coexpression module in our study also suggest striatum subregion specificity. At the transcriptional level, our study supports differences in the 3 circuit CSTC model associated with OCD.

An atypical N-ethylmaleimide sensitive factor enables the viability of nematode-resistant Rhg1 soybeans

N-ethylmaleimide sensitive factor (NSF) and α-soluble NSF attachment protein (α-SNAP) are essential eukaryotic housekeeping proteins that cooperatively function to sustain vesicular trafficking. The "resistance to Heterodera glycines 1" (Rhg1) locus of soybean (Glycine max) confers resistance to soybean cyst nematode, a highly damaging soybean pest. Rhg1 loci encode repeat copies of atypical α-SNAP proteins that are defective in promoting NSF function and are cytotoxic in certain contexts. Here, we discovered an unusual NSF allele (Rhg1-associated NSF on chromosome 07; NSFRAN07 ) in Rhg1+ germplasm. NSFRAN07 protein modeling to mammalian NSF/α-SNAP complex structures indicated that at least three of the five NSFRAN07 polymorphisms reside adjacent to the α-SNAP binding interface. NSFRAN07 exhibited stronger in vitro binding with Rhg1 resistance-type α-SNAPs. NSFRAN07 coexpression in planta was more protective against Rhg1 α-SNAP cytotoxicity, relative to WT NSFCh07 Investigation of a previously reported segregation distortion between chromosome 18 Rhg1 and a chromosome 07 interval now known to contain the Glyma.07G195900 NSF gene revealed 100% coinheritance of the NSFRAN07 allele with disease resistance Rhg1 alleles, across 855 soybean accessions and in all examined Rhg1+ progeny from biparental crosses. Additionally, we show that some Rhg1-mediated resistance is associated with depletion of WT α-SNAP abundance via selective loss of WT α-SNAP loci. Hence atypical coevolution of the soybean SNARE-recycling machinery has balanced the acquisition of an otherwise disruptive housekeeping protein, enabling a valuable disease resistance trait. Our findings further indicate that successful engineering of Rhg1-related resistance in plants will require a compatible NSF partner for the resistance-conferring α-SNAP.

Inseparable tandem: evolution chooses ATP and Ca2+ to control life, death and cellular signalling

From the very dawn of biological evolution, ATP was selected as a multipurpose energy-storing molecule. Metabolism of ATP required intracellular free Ca(2+) to be set at exceedingly low concentrations, which in turn provided the background for the role of Ca(2+) as a universal signalling molecule. The early-eukaryote life forms also evolved functional compartmentalization and vesicle trafficking, which used Ca(2+) as a universal signalling ion; similarly, Ca(2+) is needed for regulation of ciliary and flagellar beat, amoeboid movement, intracellular transport, as well as of numerous metabolic processes. Thus, during evolution, exploitation of atmospheric oxygen and increasingly efficient ATP production via oxidative phosphorylation by bacterial endosymbionts were a first step for the emergence of complex eukaryotic cells. Simultaneously, Ca(2+) started to be exploited for short-range signalling, despite restrictions by the preset phosphate-based energy metabolism, when both phosphates and Ca(2+) interfere with each other because of the low solubility of calcium phosphates. The need to keep cytosolic Ca(2+) low forced cells to restrict Ca(2+) signals in space and time and to develop energetically favourable Ca(2+) signalling and Ca(2+) microdomains. These steps in tandem dominated further evolution. The ATP molecule (often released by Ca(2+)-regulated exocytosis) rapidly grew to be the universal chemical messenger for intercellular communication; ATP effects are mediated by an extended family of purinoceptors often linked to Ca(2+) signalling. Similar to atmospheric oxygen, Ca(2+) must have been reverted from a deleterious agent to a most useful (intra- and extracellular) signalling molecule. Invention of intracellular trafficking further increased the role for Ca(2+) homeostasis that became critical for regulation of cell survival and cell death. Several mutually interdependent effects of Ca(2+) and ATP have been exploited in evolution, thus turning an originally unholy alliance into a fascinating success story.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'.

Linking kindling to increased glutamate release in the dentate gyrus of the hippocampus through the STXBP5/tomosyn-1 gene

INTRODUCTION

In kindling, repeated electrical stimulation of certain brain areas causes progressive and permanent intensification of epileptiform activity resulting in generalized seizures. We focused on the role(s) of glutamate and a negative regulator of glutamate release, STXBP5/tomosyn-1, in kindling.

METHODS

Stimulating electrodes were implanted in the amygdala and progression to two successive Racine stage 5 seizures was measured in wild-type and STXBP5/tomosyn-1-/- (Tom-/-) animals. Glutamate release measurements were performed in distinct brain regions using a glutamate-selective microelectrode array (MEA).

RESULTS

Naïve Tom-/- mice had significant increases in KCl-evoked glutamate release compared to naïve wild type as measured by MEA of presynaptic release in the hippocampal dentate gyrus (DG). Kindling progression was considerably accelerated in Tom-/- mice, requiring fewer stimuli to reach a fully kindled state. Following full kindling, MEA measurements of both kindled Tom+/+ and Tom-/- mice showed significant increases in KCl-evoked and spontaneous glutamate release in the DG, indicating a correlation with the fully kindled state independent of genotype. Resting glutamate levels in all hippocampal subregions were significantly lower in the kindled Tom-/- mice, suggesting possible changes in basal control of glutamate circuitry in the kindled Tom-/- mice.

CONCLUSIONS

Our studies demonstrate that increased glutamate release in the hippocampal DG correlates with acceleration of the kindling process. Although STXBP5/tomosyn-1 loss increased evoked glutamate release in naïve animals contributing to their prokindling phenotype, the kindling process can override any attenuating effect of STXBP5/tomosyn-1. Loss of this "braking" effect of STXBP5/tomosyn-1 on kindling progression may set in motion an alternative but ultimately equally ineffective compensatory response, detected here as reduced basal glutamate release.

A vesicle trafficking protein αSNAP regulates Paneth cell differentiation in vivo

A soluble N-ethylmaleimide-sensitive factor-attachment protein alpha (αSNAP) is a multifunctional scaffolding protein that regulates intracellular vesicle trafficking and signaling. In cultured intestinal epithelial cells, αSNAP has been shown to be essential for cell survival, motility, and adhesion; however, its physiologic functions in the intestinal mucosa remain unknown. In the present study, we used a mouse with a spontaneous hydrocephalus with hop gait (hyh) mutation of αSNAP to examine the roles of this trafficking protein in regulating intestinal epithelial homeostasis in vivo. Homozygous hyh mice demonstrated decreased expression of αSNAP protein in the intestinal epithelium, but did not display gross abnormalities of epithelial architecture in the colon and ileum. Such αSNAP depletion attenuated differentiation of small intestinal epithelial enteroids ex vivo. Furthermore, αSNAP-deficient mutant animals displayed reduced formation of lysozyme granules in small intestinal crypts and decreased expression of lysozyme and defensins in the intestinal mucosa, which is indicative of defects in Paneth cell differentiation. By contrast, development of Goblet cells, enteroendocrine cells, and assembly of enterocyte apical junctions was not altered in hyh mutant mice. Our data revealed a novel role of αSNAP in the intestinal Paneth cell differentiation in vivo.

Probing the structural dynamics of the SNARE recycling machine based on coarse-grained modeling

Membrane fusion in eukaryotes is driven by the formation of a four-helix bundle by three SNARE proteins. To recycle the SNARE proteins, they must be disassembled by the ATPase NSF and four SNAP proteins which together form a 20S supercomplex. Recently, the first high-resolution structures of the NSF (in both ATP and ADP state) and 20S (in four distinct states termed I, II, IIIa, and IIIb) were solved by cryo-electron microscopy (cryo-EM), which have paved the way for structure-driven studies of the SNARE recycling mechanism. To probe the structural dynamics of SNARE disassembly at amino-acid level of details, a systematic coarse-grained modeling based on an elastic network model and related analyses were performed. Our normal mode analysis of NSF, SNARE, and 20S predicted key modes of collective motions that partially account for the observed structural changes, and illuminated how the SNARE complex can be effectively destabilized by untwisting and bending motions of the SNARE complex driven by the amino-terminal domains of NSF in state II. Our flexibility analysis identified regions with high/low flexibility that coincide with key functional sites (such as the NSF-SNAPs-SNARE binding sites). A subset of hotspot residues that control the above collective motions, which will make promising targets for future mutagenesis studies were also identified. Finally, the conformational changes in 20S as induced by the transition of NSF from ATP to ADP state were modeled, and a concerted untwisting motion of SNARE/SNAPs and a sideway flip of two amino-terminal domains were observed. In sum, the findings have offered new structural and dynamic details relevant to the SNARE disassembly mechanism, and will guide future functional studies of the SNARE recycling machinery. Proteins 2016; 84:1055-1066. © 2016 Wiley Periodicals, Inc.

Recent Advances in Deciphering the Structure and Molecular Mechanism of the AAA+ ATPase N-Ethylmaleimide-Sensitive Factor (NSF)

N-ethylmaleimide-sensitive factor (NSF), first discovered in 1988, is a key factor for eukaryotic trafficking, including protein and hormone secretion and neurotransmitter release. It is a member of the AAA+ family (ATPases associated with diverse cellular activities). NSF disassembles soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes in conjunction with soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP). Structural studies of NSF and its complex with SNAREs and SNAPs (known as 20S supercomplex) started about 20years ago. Crystal structures of individual N and D2 domains of NSF and low-resolution electron microscopy structures of full-length NSF and 20S supercomplex have been reported over the years. Nevertheless, the molecular architecture of the 20S supercomplex and the molecular mechanism of NSF-mediated SNARE complex disassembly remained unclear until recently. Here we review recent atomic-resolution or near-atomic resolution structures of NSF and of the 20S supercomplex, as well as recent insights into the molecular mechanism and energy requirements of NSF. We also compare NSF with other known AAA+ family members.

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

In ciliates, unicellular representatives of the bikont branch of evolution, inter- and intracellular signalling pathways have been analysed mainly in Paramecium tetraurelia, Paramecium multimicronucleatum and Tetrahymena thermophila and in part also in Euplotes raikovi. Electrophysiology of ciliary activity in Paramecium spp. is a most successful example. Established signalling mechanisms include plasmalemmal ion channels, recently established intracellular Ca²⁺ -release channels, as well as signalling by cyclic nucleotides and Ca²⁺ . Ca²⁺ -binding proteins (calmodulin, centrin) and Ca²⁺ -activated enzymes (kinases, phosphatases) are involved. Many organelles are endowed with specific molecules cooperating in signalling for intracellular transport and targeted delivery. Among them are recently specified soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), monomeric GTPases, H⁺ -ATPase/pump, actin, etc. Little specification is available for some key signal transducers including mechanosensitive Ca²⁺ -channels, exocyst complexes and Ca²⁺ -sensor proteins for vesicle-vesicle/membrane interactions. The existence of heterotrimeric G-proteins and of G-protein-coupled receptors is still under considerable debate. Serine/threonine kinases dominate by far over tyrosine kinases (some predicted by phosphoproteomic analyses). Besides short-range signalling, long-range signalling also exists, e.g. as firmly installed microtubular transport rails within epigenetically determined patterns, thus facilitating targeted vesicle delivery. By envisaging widely different phenomena of signalling and subcellular dynamics, it will be shown (i) that important pathways of signalling and cellular dynamics are established already in ciliates, (ii) that some mechanisms diverge from higher eukaryotes and (iii) that considerable uncertainties still exist about some essential aspects of signalling.

Quantitative expression proteomics and phosphoproteomics profile of brain from PINK1 knockout mice: insights into mechanisms of familial Parkinson's disease

Parkinson's disease (PD) is an age-related, neurodegenerative motor disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta and presence of α-synuclein-containing protein aggregates. Mutations in the mitochondrial Ser/Thr kinase PTEN-induced kinase 1 (PINK1) are associated with an autosomal recessive familial form of early-onset PD. Recent studies have suggested that PINK1 plays important neuroprotective roles against mitochondrial dysfunction by phosphorylating and recruiting Parkin, a cytosolic E3 ubiquitin ligase, to facilitate elimination of damaged mitochondria via autophagy-lysosomal pathways. Loss of PINK1 in cells and animals leads to various mitochondrial impairments and oxidative stress, culminating in dopaminergic neuronal death in humans. Using a 2-D polyacrylamide gel electrophoresis proteomics approach, the differences in expressed brain proteome and phosphoproteome between 6-month-old PINK1-deficient mice and wild-type mice were identified. The observed changes in the brain proteome and phosphoproteome of mice lacking PINK1 suggest that defects in signaling networks, energy metabolism, cellular proteostasis, and neuronal structure and plasticity are involved in the pathogenesis of familial PD. Mutations in PINK1 are associated with an early-onset form of Parkinson's disease (PD). This study examines changes in the proteome and phosphoproteome of the PINK1 knockout mouse brain. Alterations were noted in several key proteins associated with: increased oxidative stress, aberrant cellular signaling, altered neuronal structure, decreased synaptic plasticity, reduced neurotransmission, diminished proteostasis networks, and altered metabolism. 14-3-3ε, 14-3-3 protein epsilon; 3-PGDH, phosphoglycerate dehydrogenase; ALDOA, aldolase A; APT1, acyl-protein thioesterase 1; CaM, calmodulin; CBR3, carbonyl reductase [NADPH] 3; ENO2, gamma-enolase; HPRT, hypoxanthine-guanine phosphoribosyltransferase; HSP70, heat-shock-related 70 kDa protein 2; IDHc, cytoplasmic isocitrate dehydrogenase [NADP+]; MAPK1, mitogen-activated protein kinase 1; MEK1, MAP kinase kinase 1; MDHc, cytoplasmic malate dehydrogenase; NFM, neurofilament medium polypeptide; NSF, N-ethylmaleimide-sensitive fusion protein; PHB, prohibitin; PINK1, PTEN-induced putative kinase 1; PPIaseA, peptidyl-prolyl cis-trans isomerase A; PSA2, proteasome subunit alpha type-2; TK, transketolase; VDAC-2, voltage-dependent anion-selective channel protein 2.

Mechanistic insights into the recycling machine of the SNARE complex

Evolutionarily conserved SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptors) proteins form a complex that drives membrane fusion in eukaryotes. The ATPase NSF (N-ethylmaleimide sensitive factor), together with SNAPs (soluble NSF attachment protein), disassembles the SNARE complex into its protein components, making individual SNAREs available for subsequent rounds of fusion. Here we report structures of ATP- and ADP-bound NSF, and the NSF/SNAP/SNARE (20S) supercomplex determined by single-particle electron cryomicroscopy at near-atomic to sub-nanometre resolution without imposing symmetry. Large, potentially force-generating, conformational differences exist between ATP- and ADP-bound NSF. The 20S supercomplex exhibits broken symmetry, transitioning from six-fold symmetry of the NSF ATPase domains to pseudo four-fold symmetry of the SNARE complex. SNAPs interact with the SNARE complex with an opposite structural twist, suggesting an unwinding mechanism. The interfaces between NSF, SNAPs, and SNAREs exhibit characteristic electrostatic patterns, suggesting how one NSF/SNAP species can act on many different SNARE complexes.

A neuroprotective function of NSF1 sustains autophagy and lysosomal trafficking in Drosophila

A common feature of many neurodegenerative diseases is the accumulation of toxic proteins that disrupt vital cellular functions. Degradative pathways such as autophagy play an important protective role in breaking down misfolded and long-lived proteins. Neurons are particularly vulnerable to defects in these pathways, but many of the details regarding the link between autophagy and neurodegeneration remain unclear. We previously found that temperature-sensitive paralytic mutants in Drosophila are enriched for those exhibiting age-dependent neurodegeneration. Here we show that one of these mutants, comatose (comt), in addition to locomotor defects, displays shortened lifespan and progressive neurodegeneration, including loss of dopaminerigic (DA) neurons. comt encodes N-ethyl-maleimide sensitive fusion protein (NSF1), which has a well-documented role in synaptic transmission. However, the neurodegenerative phenotypes we observe in comt mutants do not appear to depend on defects in synaptic transmission, but rather from their inability to sustain autophagy under stress, due at least in part to a defect in trafficking of lysosomal proteases such as cathepsin-L. Conversely, overexpression of NSF1 rescues α-synuclein-induced toxicity of DA neurons in a model of Parkinson's disease. Our results demonstrate a neuroprotective role for NSF1 that involves mediation of fusion events crucial for degradative pathways such as autophagy, providing greater understanding of cellular dysfunctions common to several neurodegenerative diseases.

N-ethylmaleimide-sensitive factor attachment protein α (αSNAP) regulates matrix adhesion and integrin processing in human epithelial cells

Integrin-based adhesion to the extracellular matrix (ECM) plays critical roles in controlling differentiation, survival, and motility of epithelial cells. Cells attach to the ECM via dynamic structures called focal adhesions (FA). FA undergo constant remodeling mediated by vesicle trafficking and fusion. A soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein α (αSNAP) is an essential mediator of membrane fusion; however, its roles in regulating ECM adhesion and cell motility remain unexplored. In this study, we found that siRNA-mediated knockdown of αSNAP induced detachment of intestinal epithelial cells, whereas overexpression of αSNAP increased ECM adhesion and inhibited cell invasion. Loss of αSNAP impaired Golgi-dependent glycosylation and trafficking of β1 integrin and decreased phosphorylation of focal adhesion kinase (FAK) and paxillin resulting in FA disassembly. These effects of αSNAP depletion on ECM adhesion were independent of apoptosis and NSF. In agreement with our previous reports that Golgi fragmentation mediates cellular effects of αSNAP knockdown, we found that either pharmacologic or genetic disruption of the Golgi recapitulated all the effects of αSNAP depletion on ECM adhesion. Furthermore, our data implicates β1 integrin, FAK, and paxillin in mediating the observed pro-adhesive effects of αSNAP. These results reveal novel roles for αSNAP in regulating ECM adhesion and motility of epithelial cells.

Processive ATP-driven substrate disassembly by the N-ethylmaleimide-sensitive factor (NSF) molecular machine

SNARE proteins promote membrane fusion by forming a four-stranded parallel helical bundle that brings the membranes into close proximity. Post-fusion, the complex is disassembled by an AAA+ ATPase called N-ethylmaleimide-sensitive factor (NSF). We present evidence that NSF uses a processive unwinding mechanism to disassemble SNARE proteins. Using a real-time disassembly assay based on fluorescence dequenching, we correlate NSF-driven disassembly rates with the SNARE-activated ATPase activity of NSF. Neuronal SNAREs activate the ATPase rate of NSF by ∼26-fold. One SNARE complex takes an average of ∼5 s to disassemble in a process that consumes ∼50 ATP. Investigations of substrate requirements show that NSF is capable of disassembling a truncated SNARE substrate consisting of only the core SNARE domain, but not an unrelated four-stranded coiled-coil. NSF can also disassemble an engineered double-length SNARE complex, suggesting a processive unwinding mechanism. We further investigated processivity using single-turnover experiments, which show that SNAREs can be unwound in a single encounter with NSF. We propose a processive helicase-like mechanism for NSF in which ∼1 residue is unwound for every hydrolyzed ATP molecule.

A critical role for protein degradation in the nucleus accumbens core in cocaine reward memory

The intense associative memories that develop between cocaine-paired contexts and rewarding stimuli contribute to cocaine seeking and relapse. Previous studies have shown impairment in cocaine reward memories by manipulating a labile state induced by memory retrieval, but the mechanisms that underlie the destabilization of cocaine reward memory are unknown. In this study, using a Pavlovian cocaine-induced conditioned place preference (CPP) procedure in rats, we tested the contribution of ubiquitin-proteasome system-dependent protein degradation in destabilization of cocaine reward memory. First, we found that polyubiquitinated protein expression levels and polyubiquitinated N-ethylmaleimide-sensitive fusion (NSF) markedly increased 15 min after retrieval while NSF protein levels decreased 1 h after retrieval in the synaptosomal membrane fraction in the nucleus accumbens (NAc) core. We then found that infusion of the proteasome inhibitor lactacystin into the NAc core prevented the impairment of memory reconsolidation induced by the protein synthesis inhibitor anisomycin and reversed the effects of anisomycin on NSF and glutamate receptor 2 (GluR2) protein levels in the synaptosomal membrane fraction in the NAc core. We also found that lactacystin infusion into the NAc core but not into the shell immediately after extinction training sessions inhibited CPP extinction and reversed the extinction training-induced decrease in NSF and GluR2 in the synaptosomal membrane fraction in the NAc core. Finally, infusions of lactacystin by itself into the NAc core immediately after each training session or before the CPP retrieval test had no effect on the consolidation and retrieval of cocaine reward memory. These findings suggest that ubiquitin-proteasome system-dependent protein degradation is critical for retrieval-induced memory destabilization.

Transcriptomic profiling of human peritumoral neocortex tissues revealed genes possibly involved in tumor-induced epilepsy

The molecular mechanism underlying tumor-induced epileptogenesis is poorly understood. Alterations in the peritumoral microenvironment are believed to play a significant role in inducing epileptogenesis. We hypothesize that the change of gene expression in brain peritumoral tissues may contribute to the increased neuronal excitability and epileptogenesis. To identify the genes possibly involved in tumor-induced epilepsy, a genome-wide gene expression profiling was conducted using Affymetrix HG U133 plus 2.0 arrays and RNAs derived from formalin-fixed paraffin embedded (FFPE) peritumoral cortex tissue slides from 5-seizure vs. 5-non-seizure low grade brain tumor patients. We identified many differentially expressed genes (DEGs). Seven dysregulated genes (i.e., C1QB, CALCRL, CCR1, KAL1, SLC1A2, SSTR1 and TYRO3) were validated by qRT-PCR, which showed a high concordance. Principal Component Analysis (PCA) showed that epilepsy subjects were clustered together tightly (except one sample) and were clearly separated from the non-epilepsy subjects. Molecular functional categorization showed that significant portions of the DEGs functioned as receptor activity, molecular binding including enzyme binding and transcription factor binding. Pathway analysis showed these DEGs were mainly enriched in focal adhesion, ECM-receptor interaction, and cell adhesion molecules pathways. In conclusion, our study showed that dysregulation of gene expression in the peritumoral tissues may be one of the major mechanisms of brain tumor induced-epilepsy. However, due to the small sample size of the present study, further validation study is needed. A deeper characterization on the dysregulated genes involved in brain tumor-induced epilepsy may shed some light on the management of epilepsy due to brain tumors.

A set of SNARE proteins in the contractile vacuole complex of Paramecium regulates cellular calcium tolerance and also contributes to organelle biogenesis

The contractile vacuole complex (CVC) of freshwater protists serves the extrusion of water and ions, including Ca(2+). No vesicle trafficking based on SNAREs has been detected so far in any CVC. SNAREs (soluble NSF [N-ethylmaleimide sensitive factor] attachment protein receptors) are required for membrane-to-membrane interaction, i.e. docking and fusion also in Paramecium. We have identified three v-/R- and three t/Q-SNAREs selectively in the CVC. Posttranscriptional silencing of Syb2, Syb6 or Syx2 slows down the pumping cycle; silencing of the latter two also causes vacuole swelling. Increase in extracellular Ca(2+) after Syb2, Syb6 or Syx2 silencing causes further swelling of the contractile vacuole and deceleration of its pulsation. Silencing of Syx14 or Syx15 entails lethality in the Ca(2+) stress test. Thus, the effects of silencing strictly depend on the type of the silenced SNARE and on the concentration of Ca(2+) in the medium. This shows the importance of organelle-resident SNARE functions (which may encompass the vesicular delivery of other organelle-resident proteins) for Ca(2+) tolerance. A similar principle may be applicable also to the CVC in widely different unicellular organisms. In addition, in Paramecium, silencing particularly of Syx6 causes aberrant positioning of the CVC during de novo biogenesis before cytokinesis.

Nucleotide-dependent control of internal strains in ring-shaped AAA+ motors

The AAA+ (ATPase Associated with various cellular Activities) machinery represents an extremely successful and widely used design plan for biological motors. Recently found crystal structures are beginning to reveal nucleotide-dependent conformational changes in the canonical hexameric rings of the AAA+ motors. However, the physical mechanism by which ATP binding on one subunit allosterically propagates across the entire ring remains to be found. Here we analyze and compare structural organization of three ring-shaped AAA+ motors, ClpX, HslU, and dynein. By constructing multimers using subunits of identical conformations, we find that individual subunits locally possess helical geometries with varying pitch, radius, chirality, and symmetry number. These results suggest that binding of an ATP to a subunit imposes conformational constraint that must be accommodated by more flexible nucleotide-free subunits to relieve mechanical strain on the ring. Local deformation of the ring contour and subsequent propagation of strains may be a general strategy that AAA+ motors adopt to generate force while achieving functional diversity.

Loss of a membrane trafficking protein αSNAP induces non-canonical autophagy in human epithelia

Autophagy is a catabolic process that sequesters intracellular proteins and organelles within membrane vesicles called autophagosomes with their subsequent delivery to lyzosomes for degradation. This process involves multiple fusions of autophagosomal membranes with different vesicular compartments; however, the role of vesicle fusion in autophagosomal biogenesis remains poorly understood. This study addresses the role of a key vesicle fusion regulator, soluble N-ethylmaleimide-sensitive factor attachment protein α (αSNAP), in autophagy. Small interfering RNA-mediated downregulation of αSNAP expression in cultured epithelial cells stimulated the autophagic flux, which was manifested by increased conjugation of microtubule-associated protein light chain 3 (LC3-II) and accumulation of LC3-positive autophagosomes. This enhanced autophagy developed via a non-canonical mechanism that did not require beclin1-p150-dependent nucleation, but involved Atg5 and Atg7-mediated elongation of autophagosomal membranes. Induction of autophagy in αSNAP-depleted cells was accompanied by decreased mTOR signaling but appeared to be independent of αSNAP-binding partners, N-ethylmaleimide-sensitive factor and BNIP1. Loss of αSNAP caused fragmentation of the Golgi and downregulation of the Golgi-specific GTP exchange factors, GBF1, BIG1 and BIG2. Pharmacological disruption of the Golgi and genetic inhibition of GBF1 recreated the effects of αSNAP depletion on the autophagic flux. Our study revealed a novel role for αSNAP as a negative regulator of autophagy that acts by enhancing mTOR signaling and regulating the integrity of the Golgi complex.

A membrane fusion protein αSNAP is a novel regulator of epithelial apical junctions

Tight junctions (TJs) and adherens junctions (AJs) are key determinants of the structure and permeability of epithelial barriers. Although exocytic delivery to the cell surface is crucial for junctional assembly, little is known about the mechanisms controlling TJ and AJ exocytosis. This study was aimed at investigating whether a key mediator of exocytosis, soluble N-ethylmaleimide sensitive factor (NSF) attachment protein alpha (αSNAP), regulates epithelial junctions. αSNAP was enriched at apical junctions in SK-CO15 and T84 colonic epithelial cells and in normal human intestinal mucosa. siRNA-mediated knockdown of αSNAP inhibited AJ/TJ assembly and establishment of the paracellular barrier in SK-CO15 cells, which was accompanied by a significant down-regulation of p120-catenin and E-cadherin expression. A selective depletion of p120 catenin effectively disrupted AJ and TJ structure and compromised the epithelial barrier. However, overexpression of p120 catenin did not rescue the defects of junctional structure and permeability caused by αSNAP knockdown thereby suggesting the involvement of additional mechanisms. Such mechanisms did not depend on NSF functions or induction of cell death, but were associated with disruption of the Golgi complex and down-regulation of a Golgi-associated guanidine nucleotide exchange factor, GBF1. These findings suggest novel roles for αSNAP in promoting the formation of epithelial AJs and TJs by controlling Golgi-dependent expression and trafficking of junctional proteins.

Loss of soluble N-ethylmaleimide-sensitive factor attachment protein α (αSNAP) induces epithelial cell apoptosis via down-regulation of Bcl-2 expression and disruption of the Golgi

Intracellular trafficking represents a key mechanism that regulates cell fate by participating in either prodeath or prosurvival signaling. Soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein α (αSNAP) is a well known component of vesicle trafficking machinery that mediates intermembrane fusion. αSNAP increases cell resistance to cytotoxic stimuli, although mechanisms of its prosurvival function are poorly understood. In this study, we found that either siRNA-mediated knockdown of αSNAP or expression of its dominant negative mutant induced epithelial cell apoptosis. Apoptosis was not caused by activation of the major prodeath regulators Bax and p53 and was independent of a key αSNAP binding partner, NSF. Instead, death of αSNAP-depleted cells was accompanied by down-regulation of the antiapoptotic Bcl-2 protein; it was mimicked by inhibition and attenuated by overexpression of Bcl-2. Knockdown of αSNAP resulted in impairment of Golgi to endoplasmic reticulum (ER) trafficking and fragmentation of the Golgi. Moreover, pharmacological disruption of ER-Golgi transport by brefeldin A and eeyarestatin 1 or siRNA-mediated depletion of an ER/Golgi-associated p97 ATPase recapitulated the effects of αSNAP inhibition by decreasing Bcl-2 level and triggering apoptosis. These results reveal a novel role for αSNAP in promoting epithelial cell survival by unique mechanisms involving regulation of Bcl-2 expression and Golgi biogenesis.

Kindling-induced asymmetric accumulation of hippocampal 7S SNARE complexes correlates with enhanced glutamate release

PURPOSE

To correlate kindling-associated alterations of the neurotransmitter secretory machinery, glutamate release in the trisynaptic hippocampal excitatory pathway, and the behavioral evolution of kindling-induced epileptogenesis.

METHOD

Neurotransmitter release requires the fusion of vesicle and plasma membranes; it is initiated by formation of a stable, ternary complex (7SC) of SNARE [soluble N-ethylmaleimide sensitive factor (NSF) attachment protein receptor] proteins. Quantitative Western blotting was used to monitor levels of 7SC and SNARE regulators [NSF, SV2 (synaptic vesicle protein 2)] in hippocampal synaptosomes from amygdala-kindled animals. Hippocampal synaptic glutamate release was measured in vivo with a unique microelectrode array (MEA) that uses glutamate oxidase to catalyze the breakdown of glutamate into a reporter molecule.

KEY FINDINGS

Ipsilateral hippocampal accumulation of 7SC developed with onset of amygdalar kindling, but became permanent only in animals stimulated to at least Racine stage 3; the ratio peaked and did not increase with more than two consecutive stage 5 seizures. Chronic 7SC asymmetry was seen in entorhinal cortex and the hippocampal formation, particularly in dentate gyrus (DG) and CA1, but not in the other brain areas examined. There was a strong correlation between asymmetric 7SC accumulation and increased total hippocampal SV2. Following a 30-day latent period, amplitudes of spontaneous synaptic glutamate release were enhanced in ipsilateral DG and reduced in ipsilateral CA3 of kindled animals; increased volleys of synaptic glutamate activity were seen in ipsilateral CA1.

SIGNIFICANCE

Amygdalar kindling is associated with chronic changes in the flow of glutamate signaling in the excitatory trisynaptic pathway and with early but permanent changes in the mechanics of vesicular release in ipsilateral hippocampal formation.

Structure and function of the membrane deformation AAA ATPase Vps4

The ATPase Vps4 belongs to the type-I AAA family of proteins. Vps4 functions together with a group of proteins referred to as ESCRTs in membrane deformation and fission events. These cellular functions include vesicle formation at the endosome, cytokinesis and viral budding. The highly dynamic quaternary structure of Vps4 and its interactions with a network of regulators and co-factors has made the analysis of this ATPase challenging. Nevertheless, recent advances in the understanding of the cell biology of Vps4 together with structural information and in vitro studies are guiding mechanistic models of this ATPase.

Requirements for the catalytic cycle of the N-ethylmaleimide-Sensitive Factor (NSF)

The N-ethylmaleimide-Sensitive Factor (NSF) was one of the initial members of the ATPases Associated with various cellular Activities Plus (AAA(+)) family. In this review, we discuss what is known about the mechanism of NSF action and how that relates to the mechanisms of other AAA(+) proteins. Like other family members, NSF binds to a protein complex (i.e., SNAP-SNARE complex) and utilizes ATP hydrolysis to affect the conformations of that complex. SNAP-SNARE complex disassembly is essential for SNARE recycling and sustained membrane trafficking. NSF is a homo-hexamer; each protomer is composed of an N-terminal domain, NSF-N, and two adjacent AAA-domains, NSF-D1 and NSF-D2. Mutagenesis analysis has established specific roles for many of the structural elements of NSF-D1, the catalytic ATPase domain, and NSF-N, the SNAP-SNARE binding domain. Hydrodynamic analysis of NSF, labeled with (Ni(2+)-NTA)(2)-Cy3, detected conformational differences in NSF, in which the ATP-bound conformation appears more compact than the ADP-bound form. This indicates that NSF undergoes significant conformational changes as it progresses through its ATP-hydrolysis cycle. Incorporating these data, we propose a sequential mechanism by which NSF uses NSF-N and NSF-D1 to disassemble SNAP-SNARE complexes. We also illustrate how analytical centrifugation might be used to study other AAA(+) proteins.

Dual anchoring of the GRASP membrane tether promotes trans pairing

GRASP proteins share an N-terminal GRASP domain and mediate homotypic tethering of Golgi cisternae to form extended Golgi ribbons. The golgin GM130 is thought to bind the C-terminal side of the GRASP domain to recruit GRASP65 onto the Golgi whereas stable membrane association appears to also depend on anchoring of the N terminus by myristoylation. Here, we examine the nature of the GM130/GRASP65 interaction and test whether the dual membrane contacts of the GRASP domain have a role in tethering beyond membrane recruitment. GM130 was found to contain a C-terminal PDZ ligand that binds the putative groove of the second PDZ-like domain in GRASP65. To test tethering activity independent of targeting, we took advantage of a tethering assay carried out on the mitochondrial membrane in which the GRASP membrane attachment points were individually or simultaneously substituted with mitochondrially targeted transmembrane sequences. N-terminally anchored constructs tethered only if the C terminus was also anchored; and likewise, C-terminally anchored constructs tethered only if the N terminus was anchored. One explanation for the role of this dual anchoring is that it orients the GRASP domain to prevent cis interactions within the same membrane thereby favoring trans interactions between adjacent membranes. Indeed, singly anchored GRASP constructs, although nonfunctional in tethering, interacted with one another and also bound and inhibited dually anchored constructs. This work thus elucidates the GM130/GRASP65 interaction and supports a novel orientation-based model of membrane tether regulation in which dual membrane contact orients the tethering interaction interface to favor trans over cis interactions.

NSF independent fusion of Salmonella-containing late phagosomes with early endosomes

Initial characterizations of live-Salmonella-containing early (LSEP) and late phagosomes (LSLP) in macrophages show that both phagosomes retain Rab5 and EEA1. In addition, LSEP specifically contain transferrin receptor whereas LSLP possess relatively more rabaptin-5. In contrast to LSLP, late-Salmonella-containing vacuoles in epithelial cells show significantly reduced levels of Rab5 and EEA1. Subsequent results demonstrate that both phagosomes efficiently fuse with early endosomes (EE). In contrast to LSEP, fusion between LSLP and EE is insensitive to ATPgammaS treatment. Furthermore, LSLP fuses with EE in absence of NEM-sensitive fusion factor (NSF) as well as in the presence of NSF:D1EQ mutant demonstrating that LSLP fusion with EE is NSF independent.

Comparative modeling of human NSF reveals a possible binding mode of GABARAP and GATE-16

Vesicular trafficking is an important homeostatic process in eukaryotic cells which critically relies on membrane fusion. One of the essential components of the universal membrane fusion machinery is NSF (N-ethylmaleimide-sensitive factor), a large hexameric ATPase involved in disassembly of SNARE (soluble NSF attachment protein receptor) complexes. To improve our understanding of this sophisticated molecular machine, we have modeled the structure of the NSF hexamer in two alternative assemblies. Our data suggest a mechanistic concept of the operating mode of NSF which helps to explain the functional impact of post-translational modifications and mutations reported previously. Furthermore, we propose a binding site for the ubiquitin-like proteins GABARAP and GATE-16, which is supported by experimental evidence, yielding a complex with favorable surface complementarity.

Dissecting the N-ethylmaleimide-sensitive factor: required elements of the N and D1 domains

N-Ethylmaleimide-sensitive factor (NSF) is a homo-hexameric member of the AAA(+) (ATPases associated with various cellular activities plus) family. It plays an essential role in most intracellular membrane trafficking through its binding to and disassembly of soluble NSF attachment protein (SNAP) receptor (SNARE) complexes. Each NSF protomer contains an N-terminal domain (NSF-N) and two AAA domains, a catalytic NSF-D1 and a structural NSF-D2. This study presents detailed mutagenesis analyses of NSF-N and NSF-D1, dissecting their roles in ATP hydrolysis, SNAP.SNARE binding, and complex disassembly. Our results show that a positively charged surface on NSF-N, bounded by Arg(67) and Lys(105), and the conserved residues in the central pore of NSF-D1 (Tyr(296) and Gly(298)) are involved in SNAP.SNARE binding but not basal ATP hydrolysis. Mutagenesis of Sensor 1 (Thr(373)-Arg(375)), Sensor 2 (Glu(440)-Glu(442)), and Arginine Fingers (Arg(385) and Arg(388)) in NSF-D1 shows that each region plays a discrete role. Sensor 1 is important for basal ATPase activity and nucleotide binding. Sensor 2 plays a role in ATP- and SNAP-dependent SNARE complex binding and disassembly but does so in cis and not through inter-protomer interactions. Arginine Fingers are important for SNAP.SNARE complex-stimulated ATPase activity and complex disassembly. Mutants at these residues have a dominant-negative phenotype in cells, suggesting that Arginine Fingers function in trans via inter-protomer interactions. Taken together, these data establish functional roles for many of the structural elements of the N domain and of the D1 ATP-binding site of NSF.

Platelet alpha-granules: basic biology and clinical correlates

alpha-Granules are essential to normal platelet activity. These unusual secretory granules derive their cargo from both regulated secretory and endocytotic pathways in megakaryocytes. Rare, inheritable defects of alpha-granule formation in mice and man have enabled identification of proteins that mediate cargo trafficking and alpha-granule formation. In platelets, alpha-granules fuse with the plasma membrane upon activation, releasing their cargo and increasing platelet surface area. The mechanisms that control alpha-granule membrane fusion have begun to be elucidated at the molecular level. SNAREs and SNARE accessory proteins that control alpha-granule secretion have been identified. Proteomic studies demonstrate that hundreds of bioactive proteins are released from alpha-granules. This breadth of proteins implies a versatile functionality. While initially known primarily for their participation in thrombosis and hemostasis, the role of alpha-granules in inflammation, atherosclerosis, antimicrobial host defense, wound healing, angiogenesis, and malignancy has become increasingly appreciated as the function of platelets in the pathophysiology of these processes has been defined. This review will consider the formation, release, and physiologic roles of alpha-granules with special emphasis on work performed over the last decade.

Neuroendocrine transcriptional programs adapt dynamically to the supply and demand for neuropeptides as revealed in NSF mutant zebrafish

BACKGROUND

Regulated secretion of specialized neuropeptides in the vertebrate neuroendocrine system is critical for ensuring physiological homeostasis. Expression of these cell-specific peptide markers in the differentiating hypothalamus commences prior to birth, often predating the physiological demand for secreted neuropeptides. The conserved function and spatial expression of hypothalamic peptides in vertebrates prompted us to search for critical neuroendocrine genes in newly hatched zebrafish larvae.

RESULTS

We screened mutant 5 days post-fertilization zebrafish larvae that fail to undergo visually mediated background adaptation for disruption in hypothalamic pomc expression. To our surprise, the ATPase N-ethylmaleimide sensitive factor (nsf) was identified as an essential gene for maintenance of neuroendocrine transcriptional programs during the embryo-to-larva transition. Despite normal hypothalamic development in nsf(st53) mutants, neuropeptidergic cells exhibited a dramatic loss of cell-specific markers by 5 days post-fertilization that is accompanied by elevated intracellular neuropeptide protein. Consistent with the role of NSF in vesicle-membrane fusion events and intracellular trafficking, cytoplasmic endoplasmic reticulum-like membranes accumulate in nsf(-/-) hypothalamic neurons similar to that observed for SEC18 (nsf ortholog) yeast mutants. Our data support a model in which unspent neuropeptide cargo feedbacks to extinguish transcription in neuropeptidergic cells just as they become functionally required. In support of this model we found that gnrh3 transcripts remained unchanged in pre-migratory, non-functional gonadotropin-releasing hormone (GnRH) neurons in nsf(-/-) zebrafish. Furthermore, oxytocin-like (oxtl, intp) transcripts, which are found in osmoreceptive neurons and persist in mutant zebrafish, drop precipitously after mutant zebrafish are acutely challenged with high salt.

CONCLUSION

Our analyses of nsf mutant zebrafish reveal an unexpected role for NSF in hypothalamic development, with mutant 5 days post-fertilization larvae exhibiting a stage-dependent loss of neuroendocrine transcripts and a corresponding accumulation of neuropeptides in the soma. Based on our collective findings, we speculate that neuroendocrine transcriptional programs adapt dynamically to both the supply and demand for neuropeptides to ensure adequate homeostatic responses.

Levetiracetam prevents kindling-induced asymmetric accumulation of hippocampal 7S SNARE complexes

PURPOSE

Understanding the molecular mechanisms underlying epilepsy is crucial to designing novel therapeutic regimens. This report focuses on alterations in the secretory machinery responsible for neurotransmitter (NT) release. Soluble N-ethylmaleimide sensitive factor (NSF) attachment protein receptor (SNARE) complexes mediate the fusion of synaptic vesicle and active zone membranes, thus mediating NT secretion. SNARE regulators control where and when SNARE complexes are formed. Previous studies showed an asymmetric accumulation of 7S SNARE complexes (7SC) in the ipsilateral hippocampus of kindled animals. The present studies probe the persistence of 7SC accumulation and the effect of the anticonvulsant, levetiracetam (LEV), on 7SC and SNARE regulators.

METHOD

Quantitative Western blotting was used to monitor levels of 7SC and SNARE regulators in hippocampal synaptosomes from kindled animals both before and after LEV treatment.

RESULTS

The asymmetric accumulation of 7SC is present 1-year postamygdalar kindling. The synaptic vesicle protein, synaptic vesicle protein 2 (SV2), a primary LEV-binding protein, and the SNARE regulator Tomosyn increase, whereas NSF decreases in association with this accumulation. Treatment with LEV prevented kindling-induced accumulation of SV2, but did not affect the transient increase of Tomosyn or the long-term decrease NSF. LEV treatment retarded the electrical and behavioral concomitants of amygdalar kindling coincident with a decrease in accumulation of 7SC.

CONCLUSIONS

The ipsilateral hippocampal accumulation of SNARE complexes is an altered molecular process associated with kindling that appears permanent. Kindling epileptogenesis alters synaptosomal levels of the SNARE regulators: NSF, SV2, and Tomosyn. Concomitant treatment with LEV reverses the kindling-induced 7SC accumulation and increase of SV2.

Cryo-EM structure of dodecameric Vps4p and its 2:1 complex with Vta1p

The type I AAA (ATPase associated with a variety of cellular activities) ATPase Vps4 and its co-factor Vta1p/LIP5 function in membrane remodeling events that accompany cytokinesis, multivesicular body biogenesis, and retrovirus budding, apparently by driving disassembly and recycling of membrane-associated ESCRT (endosomal sorting complex required for transport)-III complexes. Here, we present electron cryomicroscopy reconstructions of dodecameric yeast Vps4p complexes with and without their microtubule interacting and transport (MIT) N-terminal domains and Vta1p co-factors. The ATPase domains of Vps4p form a bowl-like structure composed of stacked hexameric rings. The two rings adopt dramatically different conformations, with the "upper" ring forming an open assembly that defines the sides of the bowl and the lower ring forming a closed assembly that forms the bottom of the bowl. The N-terminal MIT domains of the upper ring localize on the symmetry axis above the cavity of the bowl, and the binding of six extended Vta1p monomers causes additional density to appear both above and below the bowl. The structures suggest models in which Vps4p MIT and Vta1p domains engage ESCRT-III substrates above the bowl and help transfer them into the bowl to be pumped through the center of the dodecameric assembly.

Proteomic analysis of rat striatal synaptosomes during acrylamide intoxication at a low dose rate

We have hypothesized that acrylamide (ACR) intoxication causes cumulative nerve terminal damage by forming adducts with nucleophilic cysteine sulfhydryl groups on critical presynaptic proteins. To determine the cumulative effects of ACR on the cysteine-containing proteome of nerve terminal, we employed cleavable isotope-coded affinity tagging (ICAT) and liquid chromatography-tandem mass spectrometry. ICAT analysis uses a sulfhydryl-specific tag to identify and quantitate cysteine-containing proteins. Synaptosomes were prepared from striatum of ACR-intoxicated rats (21 mg/kg/day x 7, 14, or 21 days) and their age-matched controls. The synaptosomal proteins of each experimental group were labeled with either light (12C9--control) or heavy (13C9--ACR) ICAT reagent. Results show that ACR intoxication caused a progressive reduction in the ICAT labeling of many nerve terminal proteins. A label-free mass spectrometric approach (multidimensional protein identification) was used to show that the observed reductions in ICAT incorporation were not due to general changes in protein abundance and that ACR formed adducts with cysteine residues on peptides which also exhibited reduced ICAT incorporation. The decrease in labeling was temporally correlated to the development of neurological toxicity and confirmed previous findings that cysteine adducts of ACR accumulate as a function of exposure. The accumulation of adduct is consistent with the cumulative neurotoxicity induced by ACR and suggests that cysteine adduct formation is a necessary neuropathogenic step. Furthermore, our analyses identified specific proteins (e.g., v-ATPase, dopamine transporter, N-ethylmaleimide-sensitive factor) that were progressively and significantly adducted by ACR and might, therefore, be neurotoxicologically relevant targets.

NSF binds calcium to regulate its interaction with AMPA receptor subunit GluR2

N-ethylmaleimide-sensitive fusion protein (NSF) is essential for numerous Ca(2+)-triggered vesicle trafficking events. It functions as a molecular chaperone to regulate trafficking protein complexes such as the soluble NSF attachment protein (SNAP) receptor complex and the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-protein interacting with C-kinase (PICK1) complex. AMPAR trafficking is fundamental to processes of synaptic plasticity, which may underlie learning and memory. Changes in synaptic strength brought about by AMPAR trafficking are triggered by a post-synaptic influx of Ca(2+), which may have numerous molecular targets including PICK1. NSF binds AMPAR subunit glutamate receptor subunit 2 (GluR2) and functions to maintain receptors at the synapse. In this study, it was showed that NSF is a Ca(2+)-binding protein and that GluR2-NSF interactions are inhibited by the presence of 15 mumol/L Ca(2+). NSF Ca(2+)-binding is reciprocally inhibited by the presence of GluR2 C-terminus. Mutant of NSF that binds Ca(2+) with reduced affinity and binds GluR2 with reduced sensitivity to Ca(2+) was identied. In addition, the interaction of betaSNAP with PICK1 is sensitive to Ca(2+). This study demonstrates that the GluR2-NSF-betaSNAP-PICK1 complex is regulated directly by Ca(2+), allowing for the transduction of Ca(2+) signals into concerted alterations in protein-protein interactions to bring about changes in AMPAR trafficking during synaptic plasticity.

Asymmetric accumulation of hippocampal 7S SNARE complexes occurs regardless of kindling paradigm

Modifications of neurotransmission may contribute to the synchronization of neuronal networks that are a hallmark of epileptic seizures. In this study we examine the synaptosomal proteins involved in neurotransmitter release to determine if alterations in their interactions correlate with the chronic epileptic state. Using quantitative western blotting, we measured the levels of 7S SNARE complexes and SNARE effectors in the effected hippocampi from animals that were electrically kindled through stimulation from one of three different foci. All three kindling paradigms, amygdalar, entorhinal, and septal, were associated with an accumulation of 7S SNARE complexes in the ipsilateral hippocampus, measured 1 month after completion of kindling. Of the eight SNARE effectors examined (alpha-SNAP, NSF, SV2A/B, Munc18a/nSec1, Munc13-1, Complexins 1 and 2, and synaptotagmin I), there was a statistically significant bihemispheric increase of hippocampal SV2 and decrease of NSF upon kindling; neither by itself would be expected to account for the asymmetry of SNARE complex distribution. These data suggest that an ipsilateral hippocampal accumulation of SNARE complexes is a permanent alteration of kindling-induced epilepsy, regardless of stimulation pathway. The significance of these findings toward a molecular understanding of epilepsy will be discussed.