Internal electron transfer and structural dynamics of cd1 nitrite reductase revealed by laser CO photodissociation.

Laser photolysis techniques have been employed to investigate the internal electron transfer (eT) reaction within Pseudomonas aeruginosa nitrite reductase (Pa-NiR). We have measured the (d1--> c) internal eT rate for the wild-type protein and a site-directed mutant (Pa-NiR H327A) which has a substitution in the d1-heme binding pocket; we found the rate of eT to be fast, keT = 2.5 x 10(4) and 3.5 x 10(4) s-1 for the wild-type and mutant Pa-NiR, respectively. We also investigated the photodissociation of CO from the fully reduced proteins and observed microsecond first-order relaxations; these imply that upon breakage of the Fe2+-CO bond, both Pa-NiR and Pa-NiR H327A populate a nonequilibrium state which decays to the ground state with a complex time course that may be described by two exponential processes (k1 = 3 x 10(4) s-1 and k2 = 0.25 x 10(4) s-1). These relaxations do not have a kinetic difference spectrum characteristic of CO recombination, and therefore we conclude that Pa-NiR undergoes structural rearrangements upon dissociation of CO. The bimolecular rate of CO rebinding is 5 times faster in Pa-NiR H327A than in the wild-type enzyme (1.1 x 10(5) M-1 s-1 compared to 2 x 10(4) M-1 s-1), indicating that this mutation in the active site alters the CO diffusion properties of the protein, probably reducing steric hindrance. CO rebinding to the wild-type mixed valence enzyme (c3+d12+) which is very slow (k = 0.25 s-1) is proposed to be rate-limited by the c --> d1 internal eT event, involving the oxidized d1-heme which has a structure characteristic of the fully oxidized and partially oxidized Pa-NiR.     

ER–plasma membrane contact sites contribute to autophagosome biogenesis by regulation of local PI3P synthesis

The double‐membrane‐bound autophagosome is formed by the closure of a structure called the phagophore, origin of which is still unclear. The endoplasmic reticulum (ER) is clearly implicated in autophagosome biogenesis due to the presence of the omegasome subdomain positive for DFCP1, a phosphatidyl‐inositol‐3‐phosphate (PI3P) binding protein. Contribution of other membrane sources, like the plasma membrane (PM), is still difficult to integrate in a global picture. Here we show that ER–plasma membrane contact sites are mobilized for autophagosome biogenesis, by direct implication of the tethering extended synaptotagmins (E‐Syts) proteins. Imaging data revealed that early autophagic markers are recruited to E‐Syt‐containing domains during autophagy and that inhibition of E‐Syts expression leads to a reduction in autophagosome biogenesis. Furthermore, we demonstrate that E‐Syts are essential for autophagy‐associated PI3P synthesis at the cortical ER membrane via the recruitment of VMP1, the stabilizing ER partner of the PI3KC3 complex. These results highlight the contribution of ER–plasma membrane tethers to autophagosome biogenesis regulation and support the importance of membrane contact sites in autophagy.     

Chemical communication in mating behaviour of the slave-making ant <Emphasis Type="Italic">Polyergus rufescens</Emphasis> (Hymenoptera,Formicidae): 3-ethyl-4-methylpentanol as a critical component of the queen sex pheromone

The aim of the research reported here was to determine whether 3-ethyl-4-methylpentanol, a minor but crucial component of the sex pheromone of the North American slave-making ant species Polyergus breviceps, was also a component of the sex pheromone of the European congener Polyergus rufescens. Thus, the contents of mandibular glands of P. rufescens virgin queen were extracted and analysed. The main component of the extracts was methyl 6-methylsalicylate and 3-ethyl-4-methylpentanol was identified as one of several minor components. Further analyses showed that the insects produce mainly the (R)-enantiomer of the alcohol. Males’ responses to various blends of methyl 6-methylsalicylate with the racemate or the pure enantiomers of 3-ethyl-4- methylpentanol were tested in field behavioural bioassays. The data showed that blends of methyl 6- methylsalicylate and 3-ethyl-4-methylpentanol were strongly synergistic, with the most active ratios being biased toward the first component. The addition of other minor components to the binary blend neither increased nor decreased responses by males. Only the (R)-enantiomer of the alcohol was biologically active; its antipode did not inhibit attraction. The results are discussed in terms of the evolution of signals, and are compared with the results previously obtained for the allopatric species Polyergus breviceps. Received 12 November 2007; revised 10 January 2008; accepted 11 January 2008.     

Urinary bladder membrane permeability differentially induced by membrane lipid composition

The permeability barrier of the urothelium (covering the mammalian urinary tract) has stimulated interest in the role of the luminal membrane in the barrier function. To know how membrane lipids may affect the permeability barrier we prepare endocytic vesicles of different lipid composition entrapping a fluorescent dye (HPTS) and its quencher (DPX) using a dietary strategy (rats fed with commercial, oleic acid- or linoleic acid-enriched diets) followed by endocytosis induction. Vesicular leakage was measured by a fluorescence requenching technique. The results showed (1) endocytosed vesicles can release their content; (2) a linoleic acid-rich diet did not change either the mechanism of leakage or the amount of released material relative to the control; and (3) a oleic acid-rich diet greatly affected the mechanism of release. Thus, the dietary fatty acids can modify the urothelial cell physiology altering the pathway of endocytosed urinary fluid.     

Enzyme solid-state support assays: a surface plasmon resonance and mass spectrometry coupled study of immobilized insulin degrading enzyme

Solid-support based assays offer several advantages that are not normally available in solution. Enzymes that are anchored on gold surfaces can interact with several different molecules, opening the way to high throughput array format based assays. In this scenario, surface plasmon resonance (SPR) and mass spectrometry (MS) investigations have often been applied to analyze the interaction between immobilized enzyme and its substrate molecules in a tag-free environment. Here, we propose a SPR-MS combined experimental approach aimed at studying insulin degrading enzyme (IDE) immobilized onto gold surfaces and its ability to interact with insulin. The latter is delivered by a microfluidic system to the IDE functionalized surface and the activity of the immobilized enzyme is verified by atmospheric pressure/matrix assisted laser desorption ionization (AP/MALDI) MS analysis. The SPR experiments allow the calculation of the kinetic constants involved for the interaction between immobilized IDE and insulin molecules and evidence of IDE conformational change upon insulin binding is also obtained.     

Somatostatin: A Novel Substrate and a Modulator of Insulin-Degrading Enzyme Activity

Insulin-degrading enzyme (IDE) is an interesting pharmacological target for Alzheimer's disease (AD), since it hydrolyzes β-amyloid, producing non-neurotoxic fragments. It has also been shown that the somatostatin level reduction is a pathological feature of AD and that it regulates the neprilysin activity toward β-amyloid.In this work, we report for the first time that IDE is able to hydrolyze somatostatin [k_cat (s^− 1) = 0.38 (± 0.05); K_m (M) = 7.5 (± 0.9) × 10^− 6] at the Phe6-Phe7 amino acid bond. On the other hand, somatostatin modulates IDE activity, enhancing the enzymatic cleavage of a novel fluorogenic β-amyloid through a decrease of the K_m toward this substrate, which corresponds to the 10-25 amino acid sequence of the Aβ(1-40). Circular dichroism spectroscopy and surface plasmon resonance imaging experiments show that somatostatin binding to IDE brings about a concentration-dependent structural change of the secondary and tertiary structure(s) of the enzyme, revealing two possible binding sites. The higher affinity binding site disappears upon inactivation of IDE by ethylenediaminetetraacetic acid, which chelates the catalytic Zn²⁺ ion. As a whole, these features suggest that the modulatory effect is due to an allosteric mechanism: somatostatin binding to the active site of one IDE subunit (where somatostatin is cleaved) induces an enhancement of IDE proteolytic activity toward fluorogenic β-amyloid by another subunit. Therefore, this investigation on IDE-somatostatin interaction contributes to a more exhaustive knowledge about the functional and structural aspects of IDE and its pathophysiological implications in the amyloid deposition and somatostatin homeostasis in the brain.     

New 7,8-ethylenedioxy-2,3-benzodiazepines as noncompetitive AMPA receptor antagonists

A series of 1-aryl-3,5-dihydro-7,8-ethylenedioxy-4H-2,3-benzodiazepin-4-ones 2a-f, were synthesized and screened as anticonvulsant agents in DBA/2 mice against sound-induced seizures. The new compounds display anticonvulsant properties although the ED(50) values are higher than those of prototypes 1-aryl-3,5-dihydro-7,8-methylenedioxy-4H-2,3-benzodiazepin-4-ones (1) and GYKI 52466, well-known noncompetitive AMPA receptor antagonists. Functional tests were performed to evaluate the antagonistic activity at the AMPA and kainate receptors.     

Ultra-deep sequencing reveals the microRNA expression pattern of the human stomach

Background

While microRNAs (miRNAs) play important roles in tissue differentiation and in maintaining basal physiology, little is known about the miRNA expression levels in stomach tissue. Alterations in the miRNA profile can lead to cell deregulation, which can induce neoplasia.

Methodology/Principal Findings

A small RNA library of stomach tissue was sequenced using high-throughput SOLiD sequencing technology. We obtained 261,274 quality reads with perfect matches to the human miRnome, and 42% of known miRNAs were identified. Digital Gene Expression profiling (DGE) was performed based on read abundance and showed that fifteen miRNAs were highly expressed in gastric tissue. Subsequently, the expression of these miRNAs was validated in 10 healthy individuals by RT-PCR showed a significant correlation of 83.97% (P<0.05). Six miRNAs showed a low variable pattern of expression (miR-29b, miR-29c, miR-19b, miR-31, miR-148a, miR-451) and could be considered part of the expression pattern of the healthy gastric tissue.

Conclusions/Significance

This study aimed to validate normal miRNA profiles of human gastric tissue to establish a reference profile for healthy individuals. Determining the regulatory processes acting in the stomach will be important in the fight against gastric cancer, which is the second-leading cause of cancer mortality worldwide.     

New glycoside derivatives of carnosine and analogs resistant to carnosinase hydrolysis: synthesis and characterization of their copper(II) complexes

Carnosine (β-alanyl-L-histidine) is an endogenous dipeptide widely and abundantly distributed in muscle and nervous tissues of several animal species. Many functions have been proposed for this compound, such as antioxidant and metal ion-chelator properties. However, the main limitation on therapeutic use of carnosine on pathologies related to increased oxidative stress and/or metal ion dishomeostasis is associated with the hydrolysis by the specific dipeptidase carnosinase. Several attempts have been made to overcome this limitation. On this basis, we functionalized carnosine and its amide derivative with small sugars such as glucose and lactose. The resistance of these derivatives to the carnosinase hydrolysis was tested and compared with that of carnosine. We found that the glycoconjugation protects the dipeptide moiety from carnosinase hydrolysis, thus potentially improving the availability of carnosine. The copper(II) binding properties of all the new synthesized compounds were investigated by spectroscopic (UV-Visible and circular dichroism) and ESI-MS studies. Particularly, the new family of amide derivatives that are not significantly hydrolyzed by carnosinase is a very promising class of carnosine derivatives. The sugar moiety can act as a recognition element. These new derivatives are potentially able to act as chelating agents in the development of clinical approaches for the regulation of metal homeostasis in the field of medicinal inorganic chemistry.