Proteins functioning in synaptic transmission at the sensory to motor synapse of Aplysia

What the Gut Can Teach Us About Migraine

During gestation, cells of the brain and gut develop almost simultaneously into the central nervous system (CNS) and enteric nervous system (ENS), respectively. They remain connected via the vagal nerve lifelong. While it is well known that the brain sends signal to the gut, communication is in fact bidirectional. Just as the brain can modulate gut functioning, the gut, and likely what we ingest, can in fact influence our brain functioning. We will first review both gastrointestinal (GI) function and migraine pathophysiology and then discuss evidence linking the migraine brain to various GI disorders. Lastly, we discuss the effects of gut microbiota on brain functioning and speculate how the gut and particularly diet may affect migraine.

Sterol liganding of OSBP-related proteins (ORPs) regulates the subcellular distribution of ORP-VAPA complexes and their impacts on organelle structure

Oxysterol-binding protein (OSBP) and its homologues (ORPs) are lipid-binding/transfer proteins with affinity for oxysterols, cholesterol and glycerophospholipids. In addition to a ligand-binding domain, a majority of the ORPs carry a pleckstrin homology domain that targets organelle membranes via phosphoinositides, and a motif targeting the endoplasmic reticulum (ER) via VAMP-associated proteins (VAPs). We employed here Bimolecular Fluorescence Complementation (BiFC) to systematically assess the effects of sterol manipulation of HuH7 cells on complexes of established sterol-binding ORPs with their ER receptor, VAMP-associated protein A (VAPA). Depletion of cellular cholesterol with lipoprotein-deficient medium and Mevastatin caused concentration of OSBP-VAPA complexes and Golgi complex markers at a juxtanuclear position, an effect reversed by low-density lipoprotein treatment. A similar redistribution of OSBP-VAPA but not of sterol-binding deficient mutant OSBP(ΔELSK)-VAPA, occurred upon treatment with the high-affinity ligand, 25-hydroxycholesterol (25OHC), which reduced total and free cholesterol. ORP2-VAPA complexes, which localize in untreated cells at blob-like ER structures with associated lipid droplets, were redistributed upon treatment with the ORP2 ligand 22(R)OHC to a diffuse cytoplasmic/ER pattern and the plasma membrane. Analogously, distribution of ORP4L-VAPA complexes between the plasma membrane and vimentin intermediate filament associated compartments was modified by statin or 25OHC treatment. The treatments resulted in loss of vimentin co-localization, and sterol-binding deficient ORP4L(ΔELSR)-VAPA localized predominantly to the plasma membrane. In conclusion, treatment with statin or oxysterol ligands modify the subcellular targeting of ORP-VAPA complexes, consistent with the notion that this machinery controls lipid homeostasis and signaling at organelle interfaces.

Ligand-dependent localization and function of ORP-VAP complexes at membrane contact sites

Oxysterol-binding protein/OSBP-related proteins (ORPs) constitute a conserved family of sterol/phospholipid-binding proteins with lipid transporter or sensor functions. We investigated the spatial occurrence and regulation of the interactions of human OSBP/ORPs or the S. cerevisiae orthologs, the Osh (OSBP homolog) proteins, with their endoplasmic reticulum (ER) anchors, the VAMP-associated proteins (VAPs), by employing bimolecular fluorescence complementation and pull-down set-ups. The ORP-VAP interactions localize frequently at distinct subcellular sites, shown in several cases to represent membrane contact sites (MCSs). Using established ORP ligand-binding domain mutants and pull-down assays with recombinant proteins, we show that ORP liganding regulates the ORP-VAP association, alters the subcellular targeting of ORP-VAP complexes, or modifies organelle morphology. There is distinct protein specificity in the effects of the mutants on subcellular targeting of ORP-VAP complexes. We provide evidence that complexes of human ORP2 and VAPs at ER-lipid droplet interfaces regulate the hydrolysis of triglycerides and lipid droplet turnover. The data suggest evolutionarily conserved, complex ligand-dependent functions of ORP-VAP complexes at MCSs, with implications for cellular lipid homeostasis and signaling.

OSBP-related protein 3 (ORP3) coupling with VAMP-associated protein A regulates R-Ras activity

ORP3 is an R-Ras interacting oxysterol-binding protein homolog that regulates cell adhesion and is overexpressed in several cancers. We investigated here a novel function of ORP3 dependent on its targeting to both the endoplasmic reticulum (ER) and the plasma membrane (PM). Using biochemical and cell imaging techniques we demonstrate the mechanistic requirements for the subcellular targeting and function of ORP3 in control of R-Ras activity. We show that hyperphosphorylated ORP3 (ORP3-P) selectively interacts with the ER membrane protein VAPA, and ORP3-VAPA complexes are targeted to PM sites via the ORP3 pleckstrin homology (PH) domain. A novel FFAT (two phenylalanines in an acidic tract)-like motif was identified in ORP3; only disruption of both the FFAT-like and canonical FFAT motif abolished the phorbol-12-myristate-13-acetate (PMA) stimulated interaction of ORP3-P with VAPA. Co-expression of ORP3 and VAPA induced R-Ras activation, dependent on the interactions of ORP3 with VAPA and the PM. Consistently, downstream AktS473 phosphorylation and β1-integrin activity were enhanced by ORP3-VAPA. To conclude, phosphorylation of ORP3 controls its association with VAPA. Furthermore, we present evidence that ORP3-VAPA complexes stimulate R-Ras signaling.

A first partial Aplysia californica proteome

Aplysia proteins have not been studied systematically and it was therefore the aim of the study to carry out protein profiling in ganglia from Aplysia californica (AC). AC ganglia were extirpated, proteins extracted and run on 2DE with subsequent in-gel digestion, followed by identification of proteins by nano-LC-ESI-MS/MS on an ion trap. Proteins were identified based upon a public Aplysia EST database. Out of 408 picked spots, 276 spots were identified corresponding to 172 ESTs and 118 individual proteins. The range of sequence coverage was between 14 and 80% and the average amount of peptides used for the identification of proteins was 9 (from 3 to 24). Mean score for protein identification was 516. Comparison of protein levels between cerebral, pleural, pedal and abdominal ganglia revealed a series of significant differences including: signaling, metabolism, cytoskeleton and structural, redox, chaperone, replication/transcription and electron/proton transport proteins. The generation of a protein map complements transcriptional studies carried out in AC ganglia. The findings provide the basis for investigation into post-translational modifications, splice variants and assist in the generation of antibodies against AC proteins. Moreover, differences in protein expression between ganglia may be valuable for the design of future studies in neurobiology of AC.

The relationship between intestinal microbiota and the central nervous system in normal gastrointestinal function and disease

Although many people are aware of the communication that occurs between the gastrointestinal (GI) tract and the central nervous system, fewer know about the ability of the central nervous system to influence the microbiota or of the microbiota's influence on the brain and behavior. Within the GI tract, the microbiota have a mutually beneficial relationship with their host that maintains normal mucosal immune function, epithelial barrier integrity, motility, and nutrient absorption. Disruption of this relationship alters GI function and disease susceptibility. Animal studies suggest that perturbations of behavior, such as stress, can change the composition of the microbiota; these changes are associated with increased vulnerability to inflammatory stimuli in the GI tract. The mechanisms that underlie these alterations are likely to involve stress-induced changes in GI physiology that alter the habitat of enteric bacteria. Furthermore, experimental perturbation of the microbiota can alter behavior, and the behavior of germ-free mice differs from that of colonized mice. Gaining a better understanding of the relationship between behavior and the microbiota could provide insight into the pathogenesis of functional and inflammatory bowel disorders.

MSP domain protein-1 from Ascaris suum and its possible role in the regulation of major sperm protein-based crawling motility

Nematode sperm utilize a crawling motility based on a nematode sperm-specific cytoskeletal protein called the major sperm protein (MSP). Although MSP has no similarity to actin in sequence or structure, the motility mediated by these two proteins is nearly indistinguishable at a phenotypic level. As with the traditional actin cytoskeleton, the central component of MSP-based motility (MSP) interacts with accessory proteins that regulate polymerization and depolymerization and play a key role in cell motility. A bioinformatics approach has led to the identification of proteins with enhanced expression in the Ascaris suum male germ line, including five new proteins each containing an MSP domain. One of these MSP domain proteins (As-MDP-1) contains an MSP domain in the C-terminus and a N-terminal extension rich in prolines and alanines. The 15.6 kDa As-MDP-1 was shown to be >90% identical at the amino acid level to members of a small family of Ascaris proteins that have been shown to bind to the MSP cytoskeleton and to negatively regulate MSP fiber growth. Further, it was demonstrated that As-MDP-1 is the smallest member of the MFP1 triplet of negative regulators of MSP cytoskeleton formation. Antibodies were used to detect the presence of As-MDP-1 along the entire length of the MSP fibers suggesting that As-MDP-1 binds directly to the higher order forms of MSP. This protein has orthologues in other nematode species, is present in Ascaris in at least six allelic forms, and is likely to form multimers.

MSP domain proteins show enhanced expression in male germ line cells

Nematode sperm utilize a crawling motility based on polymerization--depolymerization of a nematode-specific cytoskeletal molecule-major sperm protein (MSP). While several proteins that interact with and regulate MSP filament formation have been identified using in vitro approaches, it is likely that additional molecules participate in vivo in the regulation of MSP cytoskeletal dynamics. By comparing EST data generated from an Ascaris suum testis germinal zone cDNA library with EST data from other tissue- and stage-specific A. suum cDNA libraries and with expression profile data from Caenorhabditis elegans, 42 genes were selected with exclusive or enhanced expression in male germ line cells. In addition to 11 protein kinases and seven protein phosphatases, 10 genes encoding proteins with protein-protein interaction domains were identified. These potential cytoskeletal modifiers included five novel MSP-domain proteins (As-MDPs). All five As-mdps were highly expressed in male germ line cells, but only As-mdp-2, 3 and 5 were transcribed exclusively in the testis. The prediction that As-MDP-1, 2 and 3 were cytosolic components and that As-MDP-4 and 5 were associated with the sperm cell membrane proteins was supported by the results of immunoblotting experiments. The 23 members of the MDP family of proteins from C. elegans were predicted to be transcribed in the testis. The findings provide additional candidates to the growing list of molecules that regulate MSP cytoskeletal dynamics.

Identification and distribution of a two-pore domain potassium channel in the CNS of Aplysia californica

A cDNA encoding a potassium channel of the two-pore domain family (K2p) of leak channels was cloned from the CNS of the marine opisthobranch Aplysia californica. This is the first sequence of the K2p family identified in molluscs and has been named AcK2p1. The deduced amino acid sequence is homologous to channels of the mammalian two-pore domain halothane inhibited (THIK) subfamily, bearing 46% identity to THIK-1 (KCNK 13) and 48% to THIK-2 (KCNK12). We used in-situ hybridization to analyze the distribution of this class of channels in the CNS. AcK2p1 is specifically expressed in many central neurons of all major ganglia including the largest identified neurons MCC, R2 and LP1. The highest expression of AcK2p1 was detected in an asymmetrical and distinct cluster of up to 30 cells located at the dorsal-medial region of the right pleural ganglion. The neuron-specific distribution seen in the molluscan CNS is consistent with data from mammals that indicate THIK is only expressed in restricted neuronal populations, suggesting its involvement in both the maintenance of neuronal phenotype and in the specific functional role of these neurons in their respective networks.

Differential regulation of endoplasmic reticulum structure through VAP-Nir protein interaction

The endoplasmic reticulum (ER) exhibits a characteristic tubular structure that is dynamically rearranged in response to specific physiological demands. However, the mechanisms by which the ER maintains its characteristic structure are largely unknown. Here we show that the integral ER-membrane protein VAP-B causes a striking rearrangement of the ER through interaction with the Nir2 and Nir3 proteins. We provide evidence that Nir (Nir1, Nir2, and Nir3)-VAP-B interactions are mediated through the conserved FFAT (two phenylalanines (FF) in acidic tract) motif present in Nir proteins. However, each interaction affects the structural integrity of the ER differently. Whereas the Nir2-VAP-B interaction induces the formation of stacked ER membrane arrays, the Nir3-VAP-B interaction leads to a gross remodeling of the ER and the bundling of thick microtubules along the altered ER membranes. In contrast, the Nir1-VAP-B interaction has no apparent effect on ER structure. We also show that the Nir2-VAP-B interaction attenuates protein export from the ER. These results demonstrate new mechanisms for the regulation of ER structure, all of which are mediated through interaction with an identical integral ER-membrane protein.

Redistribution of syntaxin mRNA in neuronal cell bodies regulates protein expression and transport during synapse formation and long-term synaptic plasticity

Syntaxin has an important role in regulating vesicle docking and fusion essential for neurotransmitter release. Here, we demonstrate that the distribution of syntaxin mRNA in cell bodies of sensory neurons (SNs) of Aplysia maintained in cell culture is affected by synapse formation, synapse stabilization, and long-term facilitation (LTF) produced by 5-HT. The distribution of the mRNA in turn regulates expression and axonal transport of the protein. Syntaxin mRNA and protein accumulated at the axon hillock of SNs during the initial phase of synapse formation. Significant numbers of granules containing syntaxin were detected in the SN axon. When synaptic strength was stable, both mRNA and protein were targeted away from the axon hillock, and the number of syntaxin granules in the SN axon was reduced. Dramatic increases in mRNA and protein accumulation at the axon hillock and number of syntaxin granules in the SN axon were produced when cultures with stable connections were treated with 5-HT that evoked LTF. Anisomycin (protein synthesis inhibitor) or KT5720 (protein kinase A inhibitor) blocked LTF, accumulation of syntaxin mRNA and protein at the axon hillock, and the increase in syntaxin granules in SN axons. The results indicate that without significant effects on overall mRNA expression, both target interaction and 5-HT via activation of protein kinase A pathway regulate expression of syntaxin and its packaging for transport into axons by influencing the distribution of its mRNA in the SN cell body.

Structure of proteins involved in synaptic vesicle fusion in neurons

The fusion of vesicles with target membranes is controlled by a complex network of protein-protein and protein-lipid interactions. Structures of the SNARE complex, synaptotagmin III, nSec1, domains of the NSF chaperone and its adaptor SNAP, and Rab3 and some of its effectors provide the framework for developing molecular models of vesicle fusion and for designing experiments to test these models.

Structural insights into the molecular mechanism of calcium-dependent vesicle-membrane fusion

The fusion of vesicles with target membranes is controlled by a complex network of protein-protein and protein-lipid interactions. Recently determined structures of the SNARE complex, synaptotagmin III, nSec1, domains of the NSF chaperone and its adaptor (SNAP), and Rab3 and some of its effectors provide the framework for developing molecular models of vesicle fusion and for designing experiments to test these models. Ultimately, knowledge of the structures of higher-order complexes and their dynamic behavior will be required to obtain a full understanding of the vesicle fusion protein machinery.

Structural insights into the molecular mechanism of Ca(2+)-dependent exocytosis

The fusion of vesicles with target membranes is controlled by a complex network of protein-protein and protein-lipid interactions. Recent structures of the SNARE complex, synaptotagmin III, nSec1, domains of NSF and its adaptor SNAP, along with Rab3 and some of its effectors, provide the framework for developing molecular models of vesicle fusion and for designing experiments to test these models. Ultimately, this knowledge of the structures of higher-order complexes and their dynamic behavior will allow us to obtain a full understanding of the vesicle fusion protein machinery.

ERG30, a VAP-33-related protein, functions in protein transport mediated by COPI vesicles

Intracellular transport of newly synthesized and mature proteins via vesicles is controlled by a large group of proteins. Here we describe a ubiquitous rat protein-endoplasmic reticulum (ER) and Golgi 30-kD protein (ERG30)-which shares structural characteristics with VAP-33, a 33-kD protein from Aplysia californica which was shown to interact with the synaptic protein VAMP. The transmembrane topology of the 30-kD ERG30 corresponds to a type II integral membrane protein, whose cytoplasmic NH(2) terminus contains a predicted coiled-coil motif. We localized ERG30 to the ER and to pre-Golgi intermediates by biochemical and immunocytochemical methods. Consistent with a role in vesicular transport, anti-ERG30 antibodies specifically inhibit intra-Golgi transport in vitro, leading to significant accumulation of COPI-coated vesicles. It appears that ERG30 functions early in the secretory pathway, probably within the Golgi and between the Golgi and the ER.

Capgras syndrome: a novel probe for understanding the neural representation of the identity and familiarity of persons

Patients with Capgras syndrome regard people whom they know well such as their parents or siblings as imposters. Here we describe a case (DS) of this syndrome who presents several novel features. DS was unusual in that his delusion was modality-specific: he claimed that his parents were imposters when he was looking at them but not when speaking to them on the telephone. Unlike normals, DS's skin conductance responses to photographs of familiar people, including his parents, were not larger in magnitude than his responses to photographs of unfamiliar people. We suggest that in this patient connections from face-processing areas in the temporal lobe to the limbic system have been damaged, a loss which may explain why he calls his parents imposters. In addition, DS was very poor at judging gaze direction. Finally, when presented with a sequence of photographs of the same model's face looking in different directions, DS asserted that they were "different women who looked just like each other'. In the absence of limbic activation, DS creates separate memory "files' of the same person, apparently because he is unable to extract and link the common denominator of successive episodic memories. Thus, far from being a medical curiosity. Capgras syndrome may help us to explore the formation of new memories caught in flagrante delicto.