LIFE CYCLE AND POPULATION STRUCTURE OF AEGLA PAULENSIS (DECAPODA: ANOMURA: AEGLIDAE)

We describe growth, longevity, sex ratio, reproductive period, and recruitment of Aegla paulensis from Jaragua Stale Park, Sao Paulo, Brazil (23 degrees 27'27.9 '' S; 46 degrees 45'32.3 '' W). The population was sampled monthly (September 2007 through August 2009) with the aid of traps. Over five thousand individuals were captured, sexed, measured (carapace length = CL) and inspected for reproductive traits (females only), and then released back to the sampling site. The pattern of the reproductive cycle was strongly seasonal (austral mid autumn through late winter), with a single recruitment pulse per year. The obtained von Bertalanffy growth equations were CL = 21.25[1-e(-0.041(t + 1.250))] and CL = 16.52[1-e(-0.049(t + 1.823))] for males and females, respectively. Males (mean CL +/- SD = 11.86 +/- 2.79 mm) attain larger sizes than females (mean CL +/- SD = 10.84 +/- 2.36 mm). Aegla paulensis reproduces twice during an estimated life span of 40.2 months for females and 33.9 months for males. Temporal variation of sex ratio showed a distinctive pattern characterized by a sequence of three distinct periods that repeated from one year to another, and which suggested that a behavioral component influence the proportion of sex in adult specimens sampled with traps during reproductive and non-reproductive periods.

Inferences of evolutionary and ecological events that influenced the population structure of Plebeia remota, a stingless bee from Brazil

The present study characterised the population genetic structure of Plebeia remota through mitochondrial DNA (mtDNA) analysis and evaluated evolutionary and ecological processes that may have contributed to the species current genetic scenario. Seventy feral nests were sampled representing four geographic regions (Cunha, Curitiba, Prudentopolis, and Blumenau). Fifteen composite mtDNA haplotypes were determined and a high genetic structure was detected among all populations. The current population structure may be a result of queen philopatry and vegetation shifts caused by palaeoclimatic changes and uplift of Brazilian coastal ranges. Finally, this study strongly suggests a revision of the taxonomic status of P. remota from the Prudentopolis region.

The Function and Three-Dimensional Structure of a Thromboxane A(2)/Cysteinyl Leukotriene-Binding Protein from the Saliva of a Mosquito Vector of the Malaria Parasite

The highly expressed D7 protein family of mosquito saliva has previously been shown to act as an anti-inflammatory mediator by binding host biogenic amines and cysteinyl leukotrienes (CysLTs). In this study we demonstrate that AnSt-D7L1, a two-domain member of this group from Anopheles stephensi, retains the CysLT binding function seen in the homolog AeD7 from Aedes aegypti but has lost the ability to bind biogenic amines. Unlike any previously characterized members of the D7 family, AnSt-D7L1 has acquired the important function of binding thromboxane A(2) (TXA(2)) and its analogs with high affinity. When administered to tissue preparations, AnSt-D7L1 abrogated Leukotriene C(4) (LTC(4))-induced contraction of guinea pig ileum and contraction of rat aorta by the TXA(2) analog U46619. The protein also inhibited platelet aggregation induced by both collagen and U46619 when administered to stirred platelets. The crystal structure of AnSt-D7L1 contains two OBP-like domains and has a structure similar to AeD(7). In AnSt-D7L1, the binding pocket of the C-terminal domain has been rearranged relative to AeD7, making the protein unable to bind biogenic amines. Structures of the ligand complexes show that CysLTs and TXA(2) analogs both bind in the same hydrophobic pocket of the N-terminal domain. The TXA(2) analog U46619 is stabilized by hydrogen bonding interactions of the omega-5 hydroxyl group with the phenolic hydroxyl group of Tyr 52. LTC(4) and occupies a very similar position to LTE(4) in the previously determined structure of its complex with AeD7. As yet, it is not known what, if any, new function has been acquired by the rearranged C-terminal domain. This article presents, to our knowledge, the first structural characterization of a protein from mosquito saliva that inhibits collagen mediated platelet activation.

Structure of disordered gold-polymer thin films using small angle x-ray scattering

We have investigated the structure of disordered gold-polymer thin films using small angle x-ray scattering and compared the results with the predictions of a theoretical model based on two approaches-a structure form factor approach and the generalized Porod law. The films are formed of polymer-embedded gold nanoclusters and were fabricated by very low energy gold ion implantation into polymethylmethacrylate (PMMA). The composite films span (with dose variation) the transition from electrically insulating to electrically conducting regimes, a range of interest fundamentally and technologically. We find excellent agreement with theory and show that the PMMA-Au films have monodispersive or polydispersive characteristics depending on the implanted ion dose. (C) 2010 American Institute of Physics. [doi:10.1063/1.3493241]

Structure of PbTe(SiO(2))/SiO(2) multilayers deposited on Si(111)

The structure of thin films composed of a multilayer of PbTe nanocrystals embedded in SiO(2), named as PbTe(SiO(2)), between homogeneous layers of amorphous SiO(2) deposited on a single-crystal Si( 111) substrate was studied by grazing-incidence small-angle X-ray scattering (GISAXS) as a function of PbTe content. PbTe(SiO(2))/SiO(2) multilayers were produced by alternately applying plasma-enhanced chemical vapour deposition and pulsed laser deposition techniques. From the analysis of the experimental GISAXS patterns, the average radius and radius dispersion of PbTe nanocrystals were determined. With increasing deposition dose the size of the PbTe nanocrystals progressively increases while their number density decreases. Analysis of the GISAXS intensity profiles along the normal to the sample surface allowed the determination of the period parameter of the layers and a structure parameter that characterizes the disorder in the distances between PbTe layers. (C) 2010 International Union of Crystallography Printed in Singapore - all rights reserved

Unraveling effects of disorder on the electronic structure of SiO(2) from first principles

We present a first-principles systematic study of the electronic structure of SiO(2) including the crystalline polymorphs alpha quartz and beta cristobalite, and different types of disorder leading to the amorphous phase. We start from calculations within density functional theory and proceed to more sophisticated quasiparticle calculations according to the GW scheme. Our results show that different origins of disorder have also different impact on atomic and electronic-density fluctuations, which affect the electronic structure and, in particular, the size of the mobility gap in each case.

Structure of (46)Ti at low excitation energy

The nucleus (46)Ti has been studied with the reaction (42)Ca((7)Li,p2n)(46)Ti at a bombarding energy of 31 MeV. Thin target foils backed with a thick Au layer were used. Five new levels of negative parity were observed. Several lifetimes have been determined with the Doppler shift attenuation method. Low-lying experimental negative-parity levels are assigned to three bands with K(pi) = 3, 0, and 4, which are interpreted in terms of the large-scale shell model, considering particle-hole excitations from d(3/2) and s(1/2) orbitals. Shell model calculations were performed using a few effective interactions. However, good agreement was not achieved in the description of either negative- or positive-parity low-lying levels.

Communication structure of cortical networks

Large-scale cortical networks exhibit characteristic topological properties that shape communication between brain regions and global cortical dynamics. Analysis of complex networks allows the description of connectedness, distance, clustering, and centrality that reveal different aspects of how the network's nodes communicate. Here, we focus on a novel analysis of complex walks in a series of mammalian cortical networks that model potential dynamics of information flow between individual brain regions. We introduce two new measures called absorption and driftness. Absorption is the average length of random walks between any two nodes, and takes into account all paths that may diffuse activity throughout the network. Driftness is the ratio between absorption and the corresponding shortest path length. For a given node of the network, we also define four related measurements, namely in-and out-absorption as well as in-and out-driftness, as the averages of the corresponding measures from all nodes to that node, and from that node to all nodes, respectively. We find that the cat thalamo-cortical system incorporates features of two classic network topologies, Erdos-Renyi graphs with respect to in-absorption and in-driftness, and configuration models with respect to out-absorption and out-driftness. Moreover, taken together these four measures separate the network nodes based on broad functional roles (visual, auditory, somatomotor, and frontolimbic).

Short-range structure of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) ceramic compounds probed by XAS and Raman scattering techniques

Ti K-edge x-ray absorption near-edge spectroscopy (XANES) and Raman scattering were used to study the solid solution effects on the structural and vibrational properties of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) with 0.0 < x < 0.40. Compared with x-ray diffraction techniques, which indicates that the average crystal symmetry changes with the substitution of Pb by Ba ions or with temperature variations for samples with x=0.00, 0.10, and 0.20, local structural probes such as XANES and Raman scattering results demonstrate that at local level, the symmetry changes are much less prominent. Theoretical XANES spectra calculation corroborate with the interpretation of the XANES experimental data.

Structure of an Odorant-Binding Protein from the Mosquito Aedes aegypti Suggests a Binding Pocket Covered by a pH-Sensitive ""Lid""

Background: The yellow fever mosquito, Aedes aegypti, is the primary vector for the viruses that cause yellow fever, mostly in tropical regions of Africa and in parts of South America, and human dengue, which infects 100 million people yearly in the tropics and subtropics. A better understanding of the structural biology of olfactory proteins may pave the way for the development of environmentally-friendly mosquito attractants and repellents, which may ultimately contribute to reduction of mosquito biting and disease transmission. Methodology: Previously, we isolated and cloned a major, female-enriched odorant-binding protein (OBP) from the yellow fever mosquito, AaegOBP1, which was later inadvertently renamed AaegOBP39. We prepared recombinant samples of AaegOBP1 by using an expression system that allows proper formation of disulfide bridges and generates functional OBPs, which are indistinguishable from native OBPs. We crystallized AaegOBP1 and determined its three-dimensional structure at 1.85 angstrom resolution by molecular replacement based on the structure of the malaria mosquito OBP, AgamOBP1, the only mosquito OBP structure known to date. Conclusion: The structure of AaegOBP1 (= AaegOBP39) shares the common fold of insect OBPs with six alpha-helices knitted by three disulfide bonds. A long molecule of polyethylene glycol (PEG) was built into the electron-density maps identified in a long tunnel formed by a crystallographic dimer of AaegOBP1. Circular dichroism analysis indicated that delipidated AaegOBP1 undergoes a pH-dependent conformational change, which may lead to release of odorant at low pH (as in the environment in the vicinity of odorant receptors). A C-terminal loop covers the binding cavity and this ""lid"" may be opened by disruption of an array of acid-labile hydrogen bonds thus explaining reduced or no binding affinity at low pH.

Partial magnetic ordering and crystal structure of the ludwigites Co(2)FeO(2)BO(3) and Ni(2)FeO(2)BO(3)

We present an extensive study of the structural, magnetic, and thermodynamic properties of the two heterometallic oxyborates: Co(2)FeO(2)BO(3) and Ni(2)FeO(2)BO(3). This has been carried out through x-ray diffraction at room temperature (RT) and 150 K, dc and ac magnetic susceptibilities, and specific-heat experiments in single crystals above 2 K. The magnetic properties of these iron ludwigites are discussed in comparison with those of the other two known homometallic ludwigites: Fe(3)O(2)BO(3) and Co(3)O(2)BO(3). In both ludwigites now studied we have found that the magnetic ordering of the Fe(3+) ions occurs at temperatures very near to which they order in Fe(3)O(2)BO(3). A freezing of the divalent ions (Co and Ni) is observed at lower temperatures. Our x-ray diffraction study of both ludwigites at RT and 150 K showed very small ionic disorder in apparent contrast with the freezing of the divalent ion spins. The structural transition that occurs in homometallic Fe(3)O(2)BO(3) has not been found in the present mixed ludwigites in the temperature range investigated.

Electronic structure of In(2)O(3) and Sn-doped In(2)O(3) by hard x-ray photoemission spectroscopy

The valence and core levels of In(2)O(3) and Sn-doped In(2)O(3) have been studied by hard x-ray photoemission spectroscopy (hv = 6000 eV) and by conventional Al K alpha (hv = 1486.6 eV) x-ray photoemission spectroscopy. The experimental spectra are compared with density-functional theory calculations. It is shown that structure deriving from electronic levels with significant In or Sn 5s character is selectively enhanced under 6000 eV excitation. This allows us to infer that conduction band states in Sn-doped samples and states at the bottom of the valence band both contain a pronounced In 5s contribution. The In 3d core line measured at hv = 1486.6 eV for both undoped and Sn-doped In(2)O(3) display an asymmetric lineshape, and may be fitted with two components associated with screened and unscreened final states. The In 3d core line spectra excited at hv = 6000 eV for the Sn-doped samples display pronounced shoulders and demand a fit with two components. The In 3d core line spectrum for the undoped sample can also be fitted with two components, although the relative intensity of the component associated with the screened final state is low, compared to excitation at 1486.6 eV. These results are consistent with a high concentration of carriers confined close to the surface of nominally undoped In(2)O(3). This conclusion is in accord with the fact that a conduction band feature observed for undoped In(2)O(3) in Al K alpha x-ray photoemission is much weaker than expected in hard x-ray photoemission.

The role of electron localization in the atomic structure of transition-metal 13-atom clusters: the example of Co(13), Rh(13), and Hf(13)

The crystalline structure of transition-metals (TM) has been widely known for several decades, however, our knowledge on the atomic structure of TM clusters is still far from satisfactory, which compromises an atomistic understanding of the reactivity of TM clusters. For example, almost all density functional theory (DFT) calculations for TM clusters have been based on local (local density approximation-LDA) and semilocal (generalized gradient approximation-GGA) exchange-correlation functionals, however, it is well known that plain DFT fails to correct the self-interaction error, which affects the properties of several systems. To improve our basic understanding of the atomic and electronic properties of TM clusters, we report a DFT study within two nonlocal functionals, namely, the hybrid HSE (Heyd, Scuseria, and Ernzerhof) and GGA + U functionals, of the structural and electronic properties of the Co(13), Rh(13), and Hf(13) clusters. For Co(13) and Rh(13), we found that improved exchange-correlation functionals decrease the stability of open structures such as the hexagonal bilayer (HBL) and double simple-cubic (DSC) compared with the compact icosahedron (ICO) structure, however, DFT-GGA, DFT-GGA + U, and DFT-HSE yield very similar results for Hf(13). Thus, our results suggest that the DSC structure obtained by several plain DFT calculations for Rh(13) can be improved by the use of improved functionals. Using the sd hybridization analysis, we found that a strong hybridization favors compact structures, and hence, a correct description of the sd hybridization is crucial for the relative energy stability. For example, the sd hybridization decreases for HBL and DSC and increases for ICO in the case of Co(13) and Rh(13), while for Hf(13), the sd hybridization decreases for all configurations, and hence, it does not affect the relative stability among open and compact configurations.

Solution structure of the human signaling protein RACK1

Background: The adaptor protein RACK1 (receptor of activated kinase 1) was originally identified as an anchoring protein for protein kinase C. RACK1 is a 36 kDa protein, and is composed of seven WD repeats which mediate its protein-protein interactions. RACK1 is ubiquitously expressed and has been implicated in diverse cellular processes involving: protein translation regulation, neuropathological processes, cellular stress, and tissue development. Results: In this study we performed a biophysical analysis of human RACK1 with the aim of obtaining low resolution structural information. Small angle X-ray scattering (SAXS) experiments demonstrated that human RACK1 is globular and monomeric in solution and its low resolution structure is strikingly similar to that of an homology model previously calculated by us and to the crystallographic structure of RACK1 isoform A from Arabidopsis thaliana. Both sedimentation velocity and sedimentation equilibrium analytical ultracentrifugation techniques showed that RACK1 is predominantly a monomer of around 37 kDa in solution, but also presents small amounts of oligomeric species. Moreover, hydrodynamic data suggested that RACK1 has a slightly asymmetric shape. The interaction of RACK1 and Ki1/57 was tested by sedimentation equilibrium. The results suggested that the association between RACK1 and Ki-1/57(122-413) follows a stoichiometry of 1:1. The binding constant (KB) observed for RACK1-Ki-1/57(122-413) interaction was of around (1.5 +/- 0.2) x 10(6) M(-1) and resulted in a dissociation constant (KD) of (0.7 +/- 0.1) x 10(-6) M. Moreover, the fluorescence data also suggests that the interaction may occur in a cooperative fashion. Conclusion: Our SAXS and analytical ultracentrifugation experiments indicated that RACK1 is predominantly a monomer in solution. RACK1 and Ki-1/57(122-413) interact strongly under the tested conditions.