Reduction in Aß-induced cell death in the hippocampus of 17ß-estradiol-treated female rats is associated with an increase in IGF-I signaling and somatostatinergic tone.

Several studies indicate that 17ß-estradiol (E2) protects against amyloid ß-peptide (Aß)-induced cell death and activates factors associated with learning and memory, a function involving the hippocampal somatostatinergic system. As alterations in somatostatin have been demonstrated in Alzheimer's disease, we examined whether E2 prevents changes in the hippocampal somatostatinergic system induced by Aß25-35 and cell death, as well as the possible involvement of leptin and insulin-like growth factor (IGF)-I signaling. We also measured the levels of Aß proteases neprilysin and insulin-degrading-enzyme. Co-administration of E2 with Aß25-35 reduced both its levels and cell death, in addition to preventing the Aß-induced depletion of some somatostatinergic parameters. Activation of leptin and IGF-I pathways increased after E2 co-administration, and this correlated with changes in the somatostatinergic system. Changes in some components of this system were inversely related with Aß levels and cell death. Moreover, neprilysin levels were increased only in Aß plus E2-treated rats and E2 prevented the Aß-induced insulin-degrading-enzyme reduction. Our results suggest that the E2-induced reduction in cell death is related to lower Aß levels, probably because of IGF-I and somatostatin modulation of Aß proteases. We asked how 17ß-estradiol (E2) protects against ß-amyloid (Aß)-induced cell death. E2 co-administration prevents Aß-produced depletion of hippocampal somatostatin (SRIF) by an IGF-I-mediated mechanism, being related this protective effect with an increase in Aß proteases. Our results suggest that the E2-induced reduction in cell death is related to lower Aß levels, probably because of SRIF modulation of Aß proteases. CREB, cAMP response element-binding protein; IGF-I, insulin-like growth factor-I; STAT3, signal transducer and activator of transcription-3.

Non-canonical residues of the marginally stable monomeric ubiquitin conjugase from goldfish are involved in binding to the C terminus of Ring 1B.

E2 ubiquitin conjugases are ~20kDa enzymes involved in ubiquitination processes in eukaryotes. The E2s are responsible for the transference of ubiquitin (Ub) to E3 enzymes, which finally transfer Ub to diverse target proteins, labelling them for degradation, localization and regulation. Although their functions are relatively well-characterized, their conformational stabilities are poorly known. In this work, we have used, as a model for our biophysical and binding studies, the E2-C from Carassius auratus (goldfish), a homologue of the human ubiquitin conjugase UbcH10. E2-C(ca) was a monomeric protein with an elongated shape; moreover, the protein was only marginally stable within a narrow pH range (from 6.0 to 8.0). We also explored the binding of E2-C(ca) towards non-canonical E3 ligases. Binding of E2-C(ca) to the C terminus of murine Ring 1B (C-Ring1B), which does not contain the RING finger of the whole Ring1B, occurred with an affinity of ~400nM, as shown by fluorescence and ITC. Furthermore, binding of E2-C(ca) to C-Ring1B did not occur at its canonical E2-loops, since residues M43 and F53, far away from those loops, were involved in binding. Thus, the C-Ring1B-interacting region of E2-C(ca) comprises the first ß-strand and nearby residues.

Mutation of Ser-50 and Cys-66 in Snapin modulates protein structure and stability.

Snapin is a 15 kDa protein present in neuronal and non-neuronal cells that has been implicated in the regulation of exocytosis and endocytosis. Protein kinase A (PKA) phosphorylates Snapin at Ser-50, modulating its function. Likewise, mutation of Cys-66, which mediates protein dimerization, impairs its cellular activity. Here, we have investigated the impact of mutating these two positions on protein oligomerization, structure, and thermal stability, along with the interaction with SNARE proteins. We found that recombinant purified Snapin in solution appears mainly as dimers in equilibrium with tetramers. The protein exhibits modest secondary structure elements and notable thermal stability. Mutation of Cys-66 to Ser abolished subunit dimerization, but not higher-order oligomers. This mutant augmented the presence of α-helical structure and slightly increased the protein thermal stability. Similarly, the S50A mutant, mimicking the unphosphorylated protein, also exhibited a higher helical secondary structure content than the wild type, along with greater thermal stability. In contrast, replacement of Ser-50 with Asp (S50D), emulating the protein-phosphorylated state, produced a loss of α-helical structure, concomitant with a decrease in protein thermal stability. In vitro, the wild type and mutants weakly interacted with SNAP-25 and the reconstituted SNARE complex, although S50D exhibited the strongest binding to the SNARE complex, consistent with the observed higher cellular activity of PKA-phosphorylated Snapin. Our observations suggest that the stronger binding of S50D to SNAREs might be due to a destabilization of tetrameric assemblies of Snapin that favor the interaction of protein dimers with the SNARE proteins. Therefore, phosphorylation of Ser-50 has an important impact on the protein structure and stability that appears to underlie its functional modulation.

Stability and binding of the phosphorylated species of the N-terminal domain of enzyme I and the histidine phosphocarrier protein from the Streptomyces coelicolor phosphoenolpyruvate:sugar phosphotransferase system.

The phosphotransferase system (PTS) is involved in the use of carbon sources in bacteria. It is formed by two general proteins: enzyme I (EI) and the histidine phosphocarrier (HPr), and various sugar-specific permeases. EI is formed by two domains, with the N-terminal domain (EIN) being responsible for the binding to HPr. In low-G+C Gram-positive bacteria, HPr becomes phosphorylated not only by phosphoenolpyruvate (PEP) at the active-site histidine, but also by ATP at a serine. In this work, we have characterized: (i) the stability and binding affinities between the active-site-histidine phosphorylated species of HPr and the EIN from Streptomyces coelicolor; and (ii) the stability and binding affinities of the species involving the phosphorylation at the regulatory serine of HPr(sc). Our results show that the phosphorylated active-site species of both proteins are less stable than the unphosphorylated counterparts. Conversely, the Hpr-S47D, which mimics phosphorylation at the regulatory serine, is more stable than wild-type HPr(sc) due to helical N-capping effects, as suggested by the modeled structure of the protein. Binding among the phosphorylated and unphosphorylated species is always entropically driven, but the affinity and the enthalpy vary widely.

The basic helix-loop-helix region of human neurogenin 1 is a monomeric natively unfolded protein which forms a "fuzzy" complex upon DNA binding.

Neuronal specification is regulated by the activity of transcription factors containing the basic helix-loop-helix motif (bHLH); these regulating proteins include, among others, the neurogenin (Ngn) family, related to the atonal family of genes. Neurogenin 1 (NGN1) is a 237-residue protein that contains a bHLH domain and is involved in neuronal differentiation. In this work, we synthesized the bHLH region of NGN1 (bHLHN) comprising residues 90-150 of the full-length NGN1. The domain is a monomeric natively unfolded protein with a pH-dependent premolten globule conformation, as shown by several spectroscopic techniques (namely, NMR, fluorescence, FTIR, and circular dichroism). The unfolded character of the domain also explains, first, the impossibility of its overexpression in several Escherichia coli strains and, second, its insolubility in aqueous buffers. To the best of our knowledge, this is the first extensive study of the conformational preferences of a bHLH domain under different solution conditions. Upon binding to two DNA E-boxes, the protein forms "fuzzy" complexes (that is, the complexes were not fully folded). The affinities of bHLHN for both DNA boxes were smaller than those of other bHLH domains, which might explain why the protein-DNA complexes were not fully folded.

The N-terminal tripeptide of insulin-like growth factor-I protects against beta-amyloid-induced somatostatin depletion by calcium and glycogen synthase kinase 3 beta modulation.

The protective effects of insulin-like growth factor I on the somatostatin (SRIF) system in the temporal cortex after beta-amyloid (Abeta) injury may be mediated through its N-terminal tripeptide glycine-proline-glutamate (GPE). GPE is cleaved to cyclo[Pro-Gly] (cPG), a metabolite suggested to mediate in neuroprotective actions. We evaluated the effects of GPE and cPG in the temporal cortex of Abeta25-35-treated rats on SRIF and SRIF receptor protein and mRNA levels, adenylyl cyclase activity, cell death, Abeta25-35 accumulation, cytosolic calcium levels ([Ca(2+)](c)) and the intracellular signaling mechanisms involved. GPE and cPG did not change Abeta25-35 levels, but GPE partially restored SRIF and SRIF receptor 2 protein content and mRNA levels and protected against cell death after Abeta25-35 insult, which was coincident with Akt activation and glycogen synthase kinase 3beta inhibition. In addition, GPE displaced glutamate from NMDA receptors and blocked the glutamate induced rise in cytosolic calcium in isolated rat neurons and moderately increased Ca(2+) influx per se. Our findings suggest that GPE, but not its metabolite, mimics insulin-like growth factor I effects on the SRIF system through a mechanism independent of Abeta clearance that involves modulation of calcium and glycogen synthase kinase 3beta signaling.

Inflammatory response in Parkinsonism.

Inflammatory responses have been proposed as important factors in dopaminergic neuro-degeneration in Parkinsonism. Increasing evidence suggests that the alteration of the glial microenvironment induced by neuronal degeneration could be deleterious to the remaining neurons. The activation of microglia/macrophages and reactive astrocytes may have a negative effect on the surrounding parenchyma, perpetuating the neurodegenerative process. However, this alteration may also go beyond the brain parenchyma and stimulate other inflammatory changes in other systems, inducing the release of proinflammatory cytokines and probably Acute Phase Proteins (APP) and Glucocorticoids (GC). In this work we review the latest advances in the field to provide a picture of the state of the art of studies of inflammatory responses and Parkinsonism, hopefully opening up new therapeutic perspectives for patients with Parkinson's disease.

Improvement in inflammation is associated with the protective effect of Gly-Pro-Glu and cycloprolylglycine against Aß-induced depletion of the hippocampal somatostatinergic system.

Glycine-proline-glutamate (GPE) is a cleaved tripeptide of IGF-I that can be processed to cycloprolylglycine (cPG) in the brain. IGF-I protects the hippocampal somatostatinergic system from ß-amyloid (Aß) insult and although neither IGF-I-derived peptides bind to IGF-I receptors, they exert protective actions in several neurological disorders. As their effects on the hippocampal somatostatinergic system remain unknown, the objective of this study was to evaluate if cPG and/or GPE prevent the deleterious effects of Aß25-35 infusion on this system and whether changes in intracellular-related signaling and interleukin (IL) content are involved in their protective effect. We also determined the effect of cPG or GPE co-administration with Aß25-35 on IL secretion in glial cultures and the influence of these ILs on signaling activation and somatostatin synthesis in neuronal cultures. cPG or GPE co-administration reduced Aß-induced cell death and pro-inflammatory ILs, increased IL-4 and partially avoided the reduction of components of the somatostatinergic system affected by Aß25-35. GPE increased activation of Akt and CREB and reduced GSK3ß activation and astrogliosis, whereas cPG increased phosphorylation of extracellular signal-regulated kinases. Both peptides converged in the activation of mTOR and S6 kinase. Co-administration of these peptides with Aß25-35 to glial cultures increased IL-4 and reduced IL-1ß; this release of IL-4 could be responsible for activation of Akt and increased somatostatin in neuronal cultures. Our findings suggest that cPG and GPE exert protective effects against Aß on the somatostatinergic system by a reduction of the inflammatory environment that may activate different pro-survival pathways in these neurons.

The Protective Effects of IGF-I against ß-Amyloid-related Downregulation of Hippocampal Somatostatinergic System Involve Activation of Akt and Protein Kinase A.

Somatostatin (SRIF), a neuropeptide highly distributed in the hippocampus and involved in learning and memory, is markedly reduced in the brain of Alzheimer's disease patients. The effects of insulin-like growth factor-I (IGF-I) against ß amyloid (Aß)-induced neuronal death and associated cognitive disorders have been extensively reported in experimental models of this disease. Here, we examined the effect of IGF-I on the hippocampal somatostatinergic system in Aß-treated rats and the molecular mechanisms associated with changes in this peptidergic system. Intracerebroventricular Aß25-35 administration during 14 days (300 pmol/day) to male rats increased Aß25-35 levels and cell death and markedly reduced SRIF and SRIF receptor 2 levels in the hippocampus. These deleterious effects were associated with reduced Akt and cAMP response element-binding protein (CREB) phosphorylation and activation of c-Jun N-terminal kinase (JNK). Subcutaneous IGF-I co-administration (50 µg/kg/day) reduced hippocampal Aß25-35 levels, cell death and JNK activation. In addition, IGF-I prevented the reduction in the components of the somatostatinergic system affected by Aß infusion. Its co-administration also augmented protein kinase A (PKA) activity, as well as Akt and CREB phosphorylation. These results suggest that IGF-I co-administration may have protective effects on the hippocampal somatostatinergic system against Aß insult through up-regulation of PKA activity and Akt and CREB phosphorylation.

Gly-Pro-Glu protects beta-amyloid-induced somatostatin depletion in the rat cortex.

The effect of Gly-Pro-Glu (GPE) on the somatostatinergic system of the temporal cortex in amyloid beta-peptide (Abeta) treated rats was investigated. Intracerebroventricular Abeta25-35 administration for 14 days (300 pmol/day) to ovariectomized rats produced a marked reduction in somatostatin (SRIF) content, SRIF receptor density and reduced the inhibitory effect of SRIF on adenylyl cyclase activity. I.p. injection of three doses (300 microg) of GPE on days 0, 6 and 12 resulted in a partial recovery of the parameters affected by Abeta25-35 administration. These results indicate that GPE may have an in vivo effect protecting the temporal cortical somatostatinergic system from Abeta insult.

The isolated N terminus of Ring1B is a well-folded, monomeric fragment with native-like structure.

The Polycomb group (PcG) proteins assemble into Polycomb repressive complexes (PRCs), PRC1 and PRC2, which act as general transcriptional repressors. PRC1 comprises a variety of biochemical entities endowed with histone H2A monoubiquitylation activity conferred by really interesting new gene (RING) finger E3 ubiquitin ligases Ring1A and Ring1B. All PRC1 complexes contain Ring1 proteins which are essential for Polycomb epigenetic regulation. We have been able to express the isolated N-terminal region of Ring1B, N-Ring1B, comprising the first 221 residues of the 334-residue-long Ring1B. This fragment contains the 41-residue-long RING finger motif, and flanking sequences that form an interacting platform for PcG and non-PcG proteins. We found that the N-Ring1B is a well-folded, monomeric fragment, with native-like structure which unfolds irreversibly. The protein is capable of binding to an ubiquitin-conjugase protein (with an 85% of sequence similarity to the Ring1B physiological partner) with moderate affinity.

Deciphering the binding between Nupr1 and MSL1 and their DNA-repairing activity.

The stress protein Nupr1 is a highly basic, multifunctional, intrinsically disordered protein (IDP). MSL1 is a histone acetyl transferase-associated protein, known to intervene in the dosage compensation complex (DCC). In this work, we show that both Nupr1 and MSL1 proteins were recruited and formed a complex into the nucleus in response to DNA-damage, which was essential for cell survival in reply to cisplatin damage. We studied the interaction of Nupr1 and MSL1, and their binding affinities to DNA by spectroscopic and biophysical methods. The MSL1 bound to Nupr1, with a moderate affinity (2.8 µM) in an entropically-driven process. MSL1 did not bind to non-damaged DNA, but it bound to chemically-damaged-DNA with a moderate affinity (1.2 µM) also in an entropically-driven process. The Nupr1 protein bound to chemically-damaged-DNA with a slightly larger affinity (0.4 µM), but in an enthalpically-driven process. Nupr1 showed different interacting regions in the formed complexes with Nupr1 or DNA; however, they were always disordered ("fuzzy"), as shown by NMR. These results underline a stochastic description of the functionality of the Nupr1 and its other interacting partners.

Biophysical characterization of the isolated C-terminal region of the transient receptor potential vanilloid 1.

Transient receptor potential (TRP) proteins are sensory-related cation channels. TRPV subfamily responds to vanilloids, generating a Ca(2+) current. TRPV1, a thermal-sensitive non-selective ion channel, possesses six transmembrane helices and the intracellular N- and C-terminal domains. The latter contains the PIP(2) and calmodulin binding sites, the TRP domain and a temperature-responding flexible region. Although the function of C-TRPV1 is known, there are no experimental reports on its structural features. Here, we describe the conformational features of C-TRVP1, by using spectroscopic and biophysical approaches. Our results show that C-TRVP1 is an oligomeric protein, which shows features of natively unfolded proteins.

The conformational stability and biophysical properties of the eukaryotic thioredoxins of Pisum sativum are not family-conserved.

Thioredoxins (TRXs) are ubiquitous proteins involved in redox processes. About forty genes encode TRX or TRX-related proteins in plants, grouped in different families according to their subcellular localization. For instance, the h-type TRXs are located in cytoplasm or mitochondria, whereas f-type TRXs have a plastidial origin, although both types of proteins have an eukaryotic origin as opposed to other TRXs. Herein, we study the conformational and the biophysical features of TRXh1, TRXh2 and TRXf from Pisum sativum. The modelled structures of the three proteins show the well-known TRX fold. While sharing similar pH-denaturations features, the chemical and thermal stabilities are different, being PsTRXh1 (Pisum sativum thioredoxin h1) the most stable isoform; moreover, the three proteins follow a three-state denaturation model, during the chemical-denaturations. These differences in the thermal- and chemical-denaturations result from changes, in a broad sense, of the several ASAs (accessible surface areas) of the proteins. Thus, although a strong relationship can be found between the primary amino acid sequence and the structure among TRXs, that between the residue sequence and the conformational stability and biophysical properties is not. We discuss how these differences in the biophysical properties of TRXs determine their unique functions in pea, and we show how residues involved in the biophysical features described (pH-titrations, dimerizations and chemical-denaturations) belong to regions involved in interaction with other proteins. Our results suggest that the sequence demands of protein-protein function are relatively rigid, with different protein-binding pockets (some in common) for each of the three proteins, but the demands of structure and conformational stability per se (as long as there is a maintained core), are less so.

Nucleotide-induced conformational transitions in the CBS domain protein MJ0729 of Methanocaldococcus jannaschii.

Nucleotide-binding cystathionine ß-synthase (CBS) domains function as regulatory motifs in several proteins distributed through all kingdoms of life. This function has been proposed based on their affinity for adenosyl-derivatives, although the exact binding mechanisms remain largely unknown. The question of how CBS domains exactly work is relevant because in humans, several genetic diseases have been associated with mutations in those motifs. In this work, we describe the adenosyl-ligand (AMP, ATP, NADP and SAM) properties of the wild-type CBS domain protein MJ0729 from Methanocaldococcus jannaschii by using a combination of spectroscopic techniques (fluorescence, FTIR and FRET). The fluorescence results show that binding to AMP and ATP occurs with an apparent dissociation constant of ~10 µM, and interestingly enough, binding induces protein conformational changes, as shown by FTIR. On the other hand, fluorescence spectra (FRET and steady-state) did not change upon addition of NADP and SAM to MJ0729, suggesting that tryptophan and/or tyrosine residues were not involved in the recognition of those ligands; however, there were changes in the secondary structure of the protein upon addition of NADP and SAM, as shown by FTIR (thus, indicating binding to the nucleotide). Taken together, these results suggest that: (i) the adenosyl ligands bind to MJ0729 in different ways, and (ii) there are changes in the protein secondary structure upon binding of the nucleotides.

The CBS domain protein MJ0729 of Methanocaldococcus jannaschii binds DNA.

The cystathionine beta-synthase (CBS) domains function as regulatory motifs in several proteins. Elucidating how CBS domains exactly work is relevant because several genetic human diseases have been associated with mutations in those motifs. Here, we show, for the first time, that a CBS domain binds calf-thymus DNA and E-boxes recognized by transcription factors. We have carried out the DNA-binding characterization of the CBS domain protein MJ0729 from Methanocaldococcus jannaschii by biochemical and spectroscopic techniques. Binding induces conformational changes in the protein, and involves the sole tryptophan residue. The apparent dissociation constant for the E-boxes is ∼10 µM. These results suggest that CBS domains might interact with DNA.

Evidence of non-functional redundancy between two pea h-type thioredoxins by specificity and stability studies.

The largest group of plant thioredoxins (TRXs) consists of the so-called h-type; their great number raises questions about their specific or redundant roles in plant cells. Pisum sativum thioredoxin h1 (PsTRXh1) and Pisum sativum thioredoxin h2 (PsTRXh2) are both h-type TRXs from pea (Pisum sativum) previously identified and biochemically characterized. While both are involved in redox regulation and show a high-sequence identity (60%), they display different behavior during in vitro and in vivo assays. In this work, we show that these two proteins display different specificity in the capturing of protein targets in vitro, by the use of a new stringent method. PsTRXh2 interacted with classical antioxidant proteins, whereas PsTRXh1 showed a completely different pattern of targeted proteins, and was able to capture a transcription factor. We also showed that the two proteins display very different thermal and chemical stabilities. We suggest that the differences in thermal and chemical stability point to a distinct and characteristic pattern of protein specificity.

17Beta-estradiol protects depletion of rat temporal cortex somatostatinergic system by beta-amyloid.

Estradiol prevents amyloid-beta peptide (Abeta)-induced cell death through estrogen receptors (ERs) and modulates somatostatin (SRIF) responsiveness in the rat brain. As intracerebroventricular (ICV) Abeta25-35 administration reduces SRIFergic tone in the temporal cortex of ovariectomized (Ovx) rats, we asked whether 17beta-estradiol (E2) treatment can restore the Abeta25-35 induced changes in SRIF content, SRIF receptor density and adenylyl cyclase (AC) activity, as well as if these effects are mediated by ERs. E2 treatment did not change Abeta25-35 levels in the temporal cortex, but partially restored the SRIFergic parameters affected by Abeta insult and decreased cell death, which was correlated with Akt activation. The ER antagonist ICI 182,780 prevented the protective effect of E2 on sst2 levels, but did not modify SRIF levels. Furthermore, ICI 182,780 treatment further decreased sst2 protein and mRNA levels when administered alone to Abeta25-35-treated rats, suggesting that it may block the effects of endogenous estrogens. These findings indicate that E2 protects the temporal cortical SRIFergic system from Abeta-induced depletion independently of Abeta accumulation.