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91.
de las Nieves Peltzer M Roques N Poinsot V Aguilar OM Batut J Capela D 《Molecular plant-microbe interactions : MPMI》2008,21(9):1232-1241
Some Sinorhizobium meliloti mutants in genes involved in isoleucine, valine, and leucine biosynthesis were previously described as being unable to induce nodule formation on host plants. Here, we present a reappraisal of the interconnection between the branched-chain amino acid biosynthesis pathway and the nodulation process in S. meliloti. We characterized the symbiotic phenotype of seven mutants that are auxotrophic for isoleucine, valine, or leucine in two closely related S. meliloti strains, 1021 and 2011. We showed that all mutants were similarly impaired for nodulation and infection of the Medicago sativa host plant. In most cases, the nodulation phenotype was fully restored by the addition of the missing amino acids to the plant growth medium. This strongly suggests that auxotrophy is the cause of the nodulation defect of these mutants. However, we confirmed previous findings that ilvC and ilvD2 mutants in the S. meliloti 1021 genetic background could not be restored to nodulation by supplementation with exogenous amino acids even though their Nod factor production appeared to be normal. 相似文献
92.
Relative contribution of AtHAK5 and AtAKT1 to K+ uptake in the high‐affinity range of concentrations
Francisco Rubio Manuel Nieves‐Cordones Fernando Alemán Vicente Martínez 《Physiologia plantarum》2008,134(4):598-608
The relative contribution of the high‐affinity K+ transporter AtHAK5 and the inward rectifier K+ channel AtAKT1 to K+ uptake in the high‐affinity range of concentrations was studied in Arabidopsis thaliana ecotype Columbia (Col‐0). The results obtained with wild‐type lines, with T‐DNA insertion in both genes and specific uptake inhibitors, show that AtHAK5 and AtAKT1 mediate the ‐sensitive and the Ba2+‐sensitive components of uptake, respectively, and that they are the two major contributors to uptake in the high‐affinity range of Rb+ concentrations. Using Rb+ as a K+ analogue, it was shown that AtHAK5 mediates absorption at lower Rb+ concentrations than AtAKT1 and depletes external Rb+ to values around 1 μM. Factors such as the presence of K+ or during plant growth determine the relative contribution of each system. The presence of in the growth solution inhibits the induction of AtHAK5 by K+ starvation. In K+‐starved plants grown without , both systems are operative, but when is present in the growth solution, AtAKT1 is probably the only system mediating Rb+ absorption, and the capacity of the roots to deplete Rb+ is reduced. 相似文献
93.
Boris F. Krasnikov Chin-Hsiang Chien Regina Nostramo John T. Pinto Edward Nieves Myrasol Callaway Jin Sun Kay Huebner Arthur J.L. Cooper 《Biochimie》2009,91(9):1072-1080
The present report identifies the enzymatic substrates of a member of the mammalian nitrilase-like (Nit) family. Nit2, which is widely distributed in nature, has been suggested to be a tumor suppressor protein. The protein was assumed to be an amidase based on sequence homology to other amidases and on the presence of a putative amidase-like active site. This assumption was recently confirmed by the publication of the crystal structure of mouse Nit2. However, the in vivo substrates were not previously identified. Here we report that rat liver Nit2 is ω-amidodicarboxylate amidohydrolase (E.C. 3.5.1.3; abbreviated ω-amidase), a ubiquitously expressed enzyme that catalyzes a variety of amidase, transamidase, esterase and transesterification reactions. The in vivo amidase substrates are α-ketoglutaramate and α-ketosuccinamate, generated by transamination of glutamine and asparagine, respectively. Glutamine transaminases serve to salvage a number of α-keto acids generated through non-specific transamination reactions (particularly those of the essential amino acids). Asparagine transamination appears to be useful in mitochondrial metabolism and in photorespiration. Glutamine transaminases play a particularly important role in transaminating α-keto-γ-methiolbutyrate, a key component of the methionine salvage pathway. Some evidence suggests that excess α-ketoglutaramate may be neurotoxic. Moreover, α-ketosuccinamate is unstable and is readily converted to a number of hetero-aromatic compounds that may be toxic. Thus, an important role of ω-amidase is to remove potentially toxic intermediates by converting α-ketoglutaramate and α-ketosuccinamate to biologically useful α-ketoglutarate and oxaloacetate, respectively. Despite its importance in nitrogen and sulfur metabolism, the biochemical significance of ω-amidase has been largely overlooked. Our report may provide clues regarding the nature of the biological amidase substrate(s) of Nit1 (another member of the Nit family), which is a well-established tumor suppressor protein), and emphasizes a) the crucial role of Nit2 in nitrogen and sulfur metabolism, and b) the possible link of Nit2 to cancer biology. 相似文献
94.
The seasonal diet and prey selection of the Southern Grey Shrike (Lanius meridionalis) was studied in two different insular habitats: shrub environments of the Canary Islands in coastal and high mountain zones.
We measured, in each season, food availability and prey size in order to determine prey size selection of shrikes along an
altitudinal gradient. Moreover, we compared the diet patterns observed with those documented on the continent, to determine
if Southern Grey Shrikes in the islands’ high mountain zone (which has a continental climate) showed seasonal diet variation
similar to those in northern continental areas. We analysed a total of 1,139 shrike pellets collected in 1 year and identified
10,179 prey items. Numerically arthropods (91%), and in terms of biomass lizards (70%) were the main prey consumed by the
shrikes. The proportions of the main prey items differed significantly between seasons and habitats. Diet in the coastal areas
was less variable than in the high mountain zone. The greater seasonal climatic variation in the high mountain zone was associated
with diet patterns similar to those found in some northern continental areas, such as the Iberian Peninsula and southern France.
Finally, shrikes selected the largest prey in the high mountain habitat. This suggests that foraging behaviour in this species
is related to climatic conditions, as the biggest and most profitable prey were consumed in the most harsh habitats. 相似文献
95.
Nahoko Yamaji Michelle J. Little Hideki Nishio Bert Billen Elba Villegas Yuji Nishiuchi Jan Tytgat Graham M. Nicholson Gerardo Corzo 《The Journal of biological chemistry》2009,284(36):24568-24582
Magi 4, now renamed δ-hexatoxin-Mg1a, is a 43-residue neurotoxic peptide from the venom of the hexathelid Japanese funnel-web spider (Macrothele gigas) with homology to δ-hexatoxins from Australian funnel-web spiders. It binds with high affinity to receptor site 3 on insect voltage-gated sodium (NaV) channels but, unlike δ-hexatoxins, does not compete for the related site 3 in rat brain despite being previously shown to be lethal by intracranial injection. To elucidate differences in NaV channel selectivity, we have undertaken the first characterization of a peptide toxin on a broad range of mammalian and insect NaV channel subtypes showing that δ-hexatoxin-Mg1a selectively slows channel inactivation of mammalian NaV1.1, NaV1.3, and NaV1.6 but more importantly shows higher affinity for insect NaV1 (para) channels. Consequently, δ-hexatoxin-Mg1a induces tonic repetitive firing of nerve impulses in insect neurons accompanied by plateau potentials. In addition, we have chemically synthesized and folded δ-hexatoxin-Mg1a, ascertained the bonding pattern of the four disulfides, and determined its three-dimensional solution structure using NMR spectroscopy. Despite modest sequence homology, we show that key residues important for the activity of scorpion α-toxins and δ-hexatoxins are distributed in a topologically similar manner in δ-hexatoxin-Mg1a. However, subtle differences in the toxin surfaces are important for the novel selectivity of δ-hexatoxin-Mg1a for certain mammalian and insect NaV channel subtypes. As such, δ-hexatoxin-Mg1a provides us with a specific tool with which to study channel structure and function and determinants for phylum- and tissue-specific activity.Voltage-gated sodium (NaV)4 channels are responsible for the generation and propagation of electrical signals in excitable cells. At least nine different genes encoding distinct NaV channels isoforms have been identified, and functionally expressed, in mammals (1). They are characterized by their sensitivity to TTX, with NaV1.5, NaV1.8, and NaV1.9 being TTX-insensitive or TTX-resistant, and the remaining subtypes being sensitive to nanomolar concentrations of TTX. In addition, localization of the subtypes also varies, with NaV1.1–1.3 mostly distributed in the central nervous system, NaV1.6–1.9 principally located in the peripheral nervous system, and NaV1.4 and NaV1.5 found in skeletal and cardiac muscle, respectively. The structural diversity of NaV channels also coincides with variations in physiological and pharmacological properties (2). In contrast, insects express only one gene (para) that undergoes extensive alternative splicing and RNA editing (3). The para-encoded NaV channel is exceptionally well conserved across diverse orders of insects, with the level of identity ranging from 87 to 98% (3). This is one reason why insecticides that target insect NaV channels have broad activity across many insect orders. In contrast, para-type NaV channels have significantly lower levels of identity with the various types of mammalian NaV channels with the level of identity typically around 50–60% (3). This explains why a high degree of phylogenetic specificity can be achieved with both NaV channel toxins and insecticides that target the NaV channel.At least seven distinct toxin-binding sites have been identified by radioligand binding and electrophysiological studies on vertebrate and insect NaV channels (4, 5). Toxins interacting with these neurotoxin receptor sites have been instrumental in the study of NaV channel topology, function, and pharmacology (6). In particular, a wide range of scorpion α-toxins, sea anemone toxins, and spider δ-hexatoxins (formerly δ-atracotoxins (7)) compete for binding to receptor site-3 on the extracellular surface of NaV channels. These polypeptide toxins all inhibit the fast inactivation of NaV channels to prolong Na+ currents (INa), despite huge diversity in primary and tertiary structures (8, 9). Nevertheless, receptor site-3 has not yet been fully characterized but is believed to involve domains DI/S5-S6, DIV/S5-S6, as well as DIV/S3-S4 (9). Most importantly, however, toxin characterization is often limited to studies using whole-cell INa or binding studies on neuronal membranes where there are mixed populations of NaV channel subtypes. For all of these toxins, the precise pattern of NaV channel subtype selectivity is either unknown or at best is incomplete.Recently, it was found that receptor site-3 was also recognized by a 43-residue spider toxin, originally named Magi 4, from the hexathelid spider Macrothele gigas (Iriomote, Japan). It binds with high affinity to insect NaV channels but, similar to scorpion α-like toxins, does not compete for the related site-3 in rat brain synaptosomes, despite being lethal by intracranial injection (10). Magi 4 shares significant homology to four δ-hexatoxin (HXTX)-1 family peptides and δ-actinopoditoxin-Mb1a (formerly δ-missulenatoxin-Mb1a; Fig. 1) but no sequence homology to scorpion α-toxins. Neurochemical studies have shown that δ-HXTX-1 toxins compete at nanomolar concentrations with both anti-mammalian (e.g. Aah2 and Lqh2) and anti-insect (e.g. LqhαIT) scorpion toxins for site-3 (11–13). The three-dimensional structures of δ-HXTX-Ar1a and δ-HXTX-Hv1a peptides have been determined (14, 15) and possess core β regions stabilized by four disulfide bonds, placing them in the inhibitory cystine knot (ICK) structural family (16).Open in a separate windowFIGURE 1.Primary and secondary structure of δ-HXTX-Mg1a. A, comparison of the primary sequence of δ-HXTX-Mg1a and δ-HXTX-Mg1b (formerly Magi 14) with currently known members of the δ-HXTX-1 family and δ-AOTX-Mb1a (δ-actinopoditoxin-Mb1a, formerly δ-missulenatoxin-Mb1a). Homologies are shown relative to δ-HXTX-Mg1a; identities are boxed in gray, and conservative substitutions are in gray italic text. Gaps (dashes) have been inserted to maximize alignment. The disulfide bonding pattern for the strictly conserved cysteine residues determined for δ-HXTX-Mg1a (this study), δ-HXTX-Ar1a (55), and δ-HXTX-Hv1a (15) is indicated above the sequences; it is assumed that δ-AOTX-Mb1a (36), δ-HXTX-Hs20.1a (8), and δ-HXTX-Hv1b (56) have the same disulfide bonding pattern. The percentage identity and homology with δ-HXTX-Mg1a is shown to the right of the sequences. B, summary of δ-HXTX-Mg1a NMR data. Sequential NOEs, classified as very weak, weak, medium, and strong, are represented by the thickness of bars. Filled diamonds indicate backbone amide protons that form hydrogen bonds. 3JNHCα coupling constants are indicated by ↑ (>8 Hz) and ↓ (<5.5 Hz). Secondary structure is shown at the bottom of the figure where rectangles represent β-turns (the type of turn is indicated in the rectangle) and arrows represent β-sheets.The aim of this study was to first determine the solution structure of Magi 4 and second to investigate the ability of Magi 4 to discriminate between different NaV channels subtypes. Here we report the tertiary structure of Magi 4 by 1H NMR and show its disulfide bonding pattern and three-dimensional structure are homologous to δ-HXTX-1 toxins. We highlight the key residues in Magi 4 that appear to be topologically similar to those residues known to be part of the pharmacophore for site-3 scorpion α-toxins, despite Magi 4 having a different overall structure to scorpion α-toxins (11). In addition, we provide a detailed characterization of the selectivity and mode of action of Magi 4 on nine cloned mammalian and insect NaV channel subtypes, including a detailed characterization on insect neurotransmission. Given that the toxin potently slows the inactivation of NaV channels, it should be renamed δ-hexatoxin-Mg1a (δ-HXTX-Mg1a) in accordance with the rational nomenclature recently proposed for naming spider peptide toxins (7) (see ArachnoServer spider toxin data base). 相似文献
96.
Walker JR Alshafie G Nieves N Ahrens J Clagett-Dame M Abou-Issa H Curley RW 《Bioorganic & medicinal chemistry》2006,14(9):3038-3048
All-trans retinoic acid analogues such as N-(4-hydroxyphenyl)retinamide (4-HPR) are effective chemopreventive and chemotherapeutic agents but their utility has been hampered by dose-limiting side effects. The glucuronide derivatives of 4-HPR, the oxygen-linked 4-HPROG and the carbon-linked 4-HPRCG, have been found to be more effective agents. The synthetic route to the fully C-linked analogue of 4-HPROG (4-HBRCG), which employs Suzuki coupling and Umpolung chemistries as key methodologies, is shown. The results of this study show 4-HBRCG to be an effective chemotherapeutic agent in a rat mammary tumor model while being devoid of classical retinoid toxicities. 相似文献
97.
Meritxell Genovart Nieves Negre Giacomo Tavecchia Ana Bistuer Luís Parpal Daniel Oro 《PloS one》2010,5(3)
It is assumed that predators mainly prey on substandard individuals, but even though some studies partially support this idea, evidence with large sample sizes, exhaustive analysis of prey and robust analysis is lacking. We gathered data from a culling program of yellow-legged gulls killed by two methods: by the use of raptors or by shooting at random. We compared both data sets to assess whether birds of prey killed randomly or by relying on specific individual features of the prey. We carried out a meticulous post-mortem examination of individuals, and analysing multiple prey characteristics simultaneously we show that raptors did not hunt randomly, but rather preferentially predate on juveniles, sick gulls, and individuals with poor muscle condition. Strikingly, gulls with an unusually good muscle condition were also predated more than expected, supporting the mass-dependent predation risk theory. This article provides a reliable example of how natural selection may operate in the wild and proves that predators mainly prey on substandard individuals. 相似文献
98.
99.
100.
Ferrer M Guazzaroni ME Richter M García-Salamanca A Yarza P Suárez-Suárez A Solano J Alcaide M van Dillewijn P Molina-Henares MA López-Cortés N Al-Ramahi Y Guerrero C Acosta A de Eugenio LI Martínez V Marques S Rojo F Santero E Genilloud O Pérez-Pérez J Rosselló-Móra R Ramos JL 《Microbial ecology》2011,62(4):824-837
The phylogenetic and functional structure of the microbial community residing in a Ca(2+)-rich anoxic sediment of a sub-saline shallow lake (Laguna de Carrizo, initially operated as a gypsum (CaSO(4)?×?2 H(2)O) mine) was estimated by analyzing the diversity of 16S rRNA amplicons and a 3.1?Mb of consensus metagenome sequence. The lake has about half the salinity of seawater and possesses an unusual relative concentration of ions, with Ca(2+) and SO (4) (2-) being dominant. The 16S rRNA sequences revealed a diverse community with about 22% of the bacterial rRNAs being less than 94.5% similar to any rRNA currently deposited in GenBank. In addition to this, about 79% of the archaeal rRNA genes were mostly related to uncultured Euryarchaeota of the CCA47 group, which are often associated with marine and oxygen-depleted sites. Sequence analysis of assembled genes revealed that 23% of the open reading frames of the metagenome library had no hits in the database. Among annotated genes, functions related to (thio) sulfate and (thio) sulfonate-reduction and iron-oxidation, sulfur-oxidation, denitrification, synthrophism, and phototrophic sulfur metabolism were found as predominant. Phylogenetic and biochemical analyses indicate that the inherent physical-chemical characteristics of this habitat coupled with adaptation to anthropogenic activities have resulted in a highly efficient community for the assimilation of polysulfides, sulfoxides, and organosulfonates together with nitro-, nitrile-, and cyanide-substituted compounds. We discuss that the relevant microbial composition and metabolic capacities at Laguna de Carrizo, likely developed as an adaptation to thrive in the presence of moderate salinity conditions and potential toxic bio-molecules, in contrast with the properties of previously known anoxic sediments of shallow lakes. 相似文献