Catalytic activity of iron phthalocyanine for the oxidation of thiocyanate and L-cysteine anchored on Au(111) clusters

ABSTRACT

We studied the oxidation reactions of thiocyanate and L-cysteine on iron phthalocyanine (FePc) coupled via a bridging ligand of the 4-mercatopyridine (4MP) type to a gold cluster (Au₂₆), aiming to simulate a modified gold electrode. Theoretical models have been used based on the framework of density functional theory. Several mechanistic pathways are explored for the study of these reactions, finding that the most favorable mechanism involves an electron transfer process as the rate-determining step. Along the process, the ability of the gold cluster to act as an electron acceptor facilitating the reactions was detected. In addition, the proposed models presented a correlation between the energy obtained for the rate-determining step of the reaction and the experimental oxidation potentials of the thiocyanate and L-cysteine.     

LEA Gene Introns: is the Intron of Dehydrin Genes a Characteristic of the Serine-Segment?

Dehydrins, which belong to group 2 LEA proteins, are a family of intrinsically unstructured plant proteins that accumulate during the late stages of embryogenesis and in response to abiotic stresses. We have previously reported that the OpsDHN1 gene, encoding an SK₃-type acidic dehydrin protein from Opuntia streptacantha, contains an intron inserted within the sequence encoding the S-motif. Herein, we present an in silico analysis of intron sequences in dehydrin genes from mono- and dicotyledonous plants that reveals a preference for insertion within the nucleotide sequence encoding the S-motif. Sequence comparison of ten Dhn genes from Arabidopsis thaliana and the orthologous genes in Arabidopsis lyrata revealed that introns maintain considerable sequence identity and conserve the insertion pattern. Furthermore, syntenic regions were identified among eight orthologous genes of A. thaliana and A. lyrata, showing that correlated gene arrangements are conserved between these Arabidopsis species. Our study shows that most SKn-type dehydrins contain one intron that is conserved in phase and location; this intron is linked to the nucleotide sequence that encodes the S-motif.     

Genetic variability characterization of the moroccan houbara bustard (Chlamydotis undulata undulata) inferred from pedigree analysis

A Moroccan Houbara Bustard pedigree was analyzed to evaluate the genetic variability in captive breeding population using genealogical approaches. The whole Houbara breeding flock (WP) for the period 1993–2004 was made up of 531 birds comprising 346 females and 185 males. The reference population (RP) comprised 198 individuals ready for reproduction from 2000 to 2004 cohorts. The corresponding percentage of known ancestors was estimated as 98.23% for the parent generation, 41.19% for the grandparent generation and 7.00% for the great grandparents generation. The average generation interval for Houbara was computed as 4.64 years. Genetic variability loss per generation was ascertained using the effective population size (), the founder genome equivalent (fge), the effective number of ancestors and founders (fa) and (fe), respectively, for the RP and across each cohort. The results showed no bottleneck events in the breed but some loss of genetic variability just after the initiation of the conservation program. However, the annual effective population size based on the realized increase in inbreeding () was estimated to be 207 for the RP and 1,000 for the WP. With regard to conservation breeding schemes, the genealogical evidence presented here is very useful as it revealed the positive effect of migration on Houbara breeding. The mating strategies will assist in the future control and management of the genetic variability of this population. Zoo Biol. 32:366‐373, 2013. © 2012 Wiley Periodicals, Inc.     

Circadian system responses to nocturnal and diurnal hosts in the kissing bug,Triatoma infestans

ABSTRACT

Insects express diverse behavioral rhythms synchronized to environmental cycles. While circadian entrainment to light–dark cycles is ubiquitous in living organisms, synchronization to non-photic cycles may be critical for hematophagous bugs that depend on rhythmic hosts. The purpose was to determine whether Triatoma infestans are capable of synchronizing to the circadian rhythms of potential hosts with temporally distinct activity patterns; and, if so, if this synchronization occurs through masking or entrainment. Precise synchronization with the food source may be critical for the insects’ survival due to the specific predatory or defensive nature of each host. Kissing bugs were housed in a compartment in constant dark, air-flow-connected to another compartment with a nocturnal or a diurnal host; both hosts were synchronized to a light–dark cycle. The activity rhythms of kissing bugs were modulated by the daily activity rhythms of the vertebrates. Effects were a decrease in the endogenous circadian period, independent of the host being nocturnal or diurnal; in some cases relative coordination occurred and in others synchronization was clearly achieved. Moreover, splitting and bimodality arose, phenomena that were also affected by the host presence. The results indicate that T. infestans were able to detect the non-photic cycle of their potential hosts, an ability that surely facilitates feeding and hinders predation risk. Understanding triatomines behavior is of fundamental importance to the design of population control methods.     

Two Steady‐Entrainment Phases and Graded Masking Effects by Light Generate Different Circadian Chronotypes in Octodon degus

Processes involved in the operation of the circadian pacemaker are well characterized; however; little is known about what mechanisms drive the overt diurnal, nocturnal, or crepuscular behavior in a species. In this context, dual‐phasing rodents, such as Octodon degus, emerge as a useful model to decipher these keys. Two main chronotypes, nocturnal and diurnal, have been traditionally described in laboratory‐housed degus based on the percentage of activity displayed by the animals during the scotophase or photophase. However, if one considers also the entrainment phase angle during the first days following a change from LD to DD conditions, a third chronotype (intermediate)—or more properly, a continuous grading of circadian expressions between diurnal and nocturnal chronotype—can be observed. Our experiments suggest the pacemaker of the diurnal animal is entrained to the photophase, and light does not exert a negative masking effect. The pacemaker of the nocturnal degus, on the other hand, is entrained to the scotophase, and light exerts a strong negative masking effect. Finally, the intermediate chronotype is characterized by variable negative masking effect of light overlapping a pacemaker entrained to the photophase. The phase shift inversion from diurnal to nocturnal chronotype is related to the availability of a wheel in the cage, and the effect may be located downstream from the clock. However, body temperature rhythm recordings, less affected by masking effects, point to an involvement of the circadian pacemaker in chronotype differentiation, as transient entrainment cycles, and not an abrupt phase shift, were detected after providing access to the wheel. The diurnality of degus seems to be the result of a variety of mechanisms, which may explain how different processes can lead to similar chronotypes.     

Alternative Serotype Adenovirus Vaccine Vectors Elicit Memory T Cells with Enhanced Anamnestic Capacity Compared to Ad5 Vectors

The failure of the adenovirus serotype 5 (Ad5) vector-based human immunodeficiency virus type 1 (HIV-1) vaccine in the STEP study has led to the development of adenovirus vectors derived from alternative serotypes, such as Ad26, Ad35, and Ad48. We have recently demonstrated that vaccines using alternative-serotype Ad vectors confer partial protection against stringent simian immunodeficiency virus (SIV) challenges in rhesus monkeys. However, phenotypic differences between the T cell responses elicited by Ad5 and those of alternative-serotype Ad vectors remain unexplored. Here, we report the magnitude, phenotype, functionality, and recall capacity of memory T cell responses elicited in mice by Ad5, Ad26, Ad35, and Ad48 vectors expressing lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP). Our data demonstrate that memory T cells elicited by Ad5 vectors were high in magnitude but exhibited functional exhaustion and decreased anamnestic potential following secondary antigen challenge compared to Ad26, Ad35, and Ad48 vectors. These data suggest that vaccination with alternative-serotype Ad vectors offers substantial immunological advantages over Ad5 vectors, in addition to circumventing high baseline Ad5-specific neutralizing antibody titers.     

Redox-sensitive stimulation of type-1 ryanodine receptors by the scorpion toxin maurocalcine

The scorpion toxin maurocalcine acts as a high affinity agonist of the type-1 ryanodine receptor expressed in skeletal muscle. Here, we investigated the effects of the reducing agent dithiothreitol or the oxidizing reagent thimerosal on type-1 ryanodine receptor stimulation by maurocalcine. Maurocalcine addition to sarcoplasmic reticulum vesicles actively loaded with calcium elicited Ca²⁺ release from native vesicles and from vesicles pre-incubated with dithiothreitol; thimerosal addition to native vesicles after Ca²⁺ uptake completion prevented this response. Maurocalcine enhanced equilibrium [³H]-ryanodine binding to native and to dithiothreitol-treated reticulum vesicles, and increased 5-fold the apparent K_i for Mg²⁺ inhibition of [³H]-ryanodine binding to native vesicles. Single calcium release channels incorporated in planar lipid bilayers displayed a long-lived open sub-conductance state after maurocalcine addition. The fractional time spent in this sub-conductance state decreased when lowering cytoplasmic [Ca²⁺] from 10 μM to 0.1 μM or at cytoplasmic [Mg²⁺] ≥ 30 μM. At 0.1 μM [Ca²⁺], only channels that displayed poor activation by Ca²⁺ were readily activated by 5 nM maurocalcine; subsequent incubation with thimerosal abolished the sub-conductance state induced by maurocalcine. We interpret these results as an indication that maurocalcine acts as a more effective type-1 ryanodine receptor channel agonist under reducing conditions.     

An Extracellular Ion Pathway Plays a Central Role in the Cooperative Gating of a K2P K+ Channel by Extracellular pH

Proton-gated TASK-3 K⁺ channel belongs to the K_2P family of proteins that underlie the K⁺ leak setting the membrane potential in all cells. TASK-3 is under cooperative gating control by extracellular [H⁺]. Use of recently solved K_2P structures allows us to explore the molecular mechanism of TASK-3 cooperative pH gating. Tunnel-like side portals define an extracellular ion pathway to the selectivity filter. We use a combination of molecular modeling and functional assays to show that pH-sensing histidine residues and K⁺ ions mutually interact electrostatically in the confines of the extracellular ion pathway. K⁺ ions modulate the pK_a of sensing histidine side chains whose charge states in turn determine the open/closed transition of the channel pore. Cooperativity, and therefore steep dependence of TASK-3 K⁺ channel activity on extracellular pH, is dependent on an effect of the permeant ion on the channel pH_o sensors.     

Unsaturated Long Chain Free Fatty Acids Are Input Signals of the Salmonella enterica PhoP/PhoQ Regulatory System

The Salmonella enterica serovar Typhimurium PhoP/PhoQ system has largely been studied as a paradigmatic two-component regulatory system not only to dissect structural and functional aspects of signal transduction in bacteria but also to gain knowledge about the versatile devices that have evolved allowing a pathogenic bacterium to adjust to or counteract environmental stressful conditions along its life cycle. Mg²⁺ limitation, acidic pH, and the presence of cationic antimicrobial peptides have been identified as cues that the sensor protein PhoQ can monitor to reprogram Salmonella gene expression to cope with extra- or intracellular challenging conditions. In this work, we show for the first time that long chain unsaturated free fatty acids (LCUFAs) present in Salmonella growth medium are signals specifically detected by PhoQ. We demonstrate that LCUFAs inhibit PhoQ autokinase activity, turning off the expression of the PhoP-dependent regulon. We also show that LCUFAs exert their action independently of their cellular uptake and metabolic utilization by means of the β-oxidative pathway. Our findings put forth the complexity of input signals that can converge to finely tune the activity of the PhoP/PhoQ system. In addition, they provide a new potential biochemical platform for the development of antibacterial strategies to fight against Salmonella infections.