[Show abstract][Hide abstract] ABSTRACT: Chitons (class Polyplacophora) are benthic grazing molluscs with an eight-part aragonitic shell armature. The radula, a serial tooth ribbon that extends internally more than half the length of the body, is mineralised on the active feeding teeth with iron magnetite apparently as an adaptation to constant grazing on rocky substrates. As the anterior feeding teeth are eroded they are shed and replaced with a new row. The efficient mineralisation and function of the radula could hypothetically be affected by changing oceans in two ways: changes in seawater chemistry (pH and pCO2) may impact the biomineralisation pathway, potentially leading to a weaker or altered density of the feeding teeth; rising temperatures could increase activity levels in these ectothermic animals, and higher feeding rates could increase wear on the feeding teeth beyond the animals' ability to synthesise, mineralise, and replace radular rows. We therefore examined the effects of pH and temperature on growth and integrity in the radula of the chiton Leptochiton asellus. Our experiment implemented three temperature (∼10, 15, 20 °C) and two pCO2 treatments (∼400 μatm, pH 8.0; ∼2000 μatm, pH 7.5) for six treatment groups. Animals (n = 50) were acclimated to the treatment conditions for a period of 4 weeks. This is sufficient time for growth of ca. 7-9 new tooth rows or 20% turnover of the mineralised portion. There was no significant difference in the number of new (non-mineralised) teeth or total tooth row count in any treatment. Examination of the radulae via SEM revealed no differences in microwear or breakage on the feeding cusps correlating to treatment groups. The shell valves also showed no signs of dissolution. As a lineage, chitons have survived repeated shifts in Earth's climate through geological time, and at least their radulae may be robust to future perturbations.
[Show abstract][Hide abstract] ABSTRACT: Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) catalyses one of the two steps in glycolysis which generate the reduced coenzyme NADH. This reaction precedes the two ATP generating steps. Thus, inhibition of GAPDH will lead to substantially reduced energy generation. Consequently, there has been considerable interest in developing GAPDH inhibitors as anti-cancer and anti-parasitic agents. Here, we describe the biochemical characterisation of GAPDH from the common liver fluke Fasciola hepatica (FhGAPDH). The primary sequence of FhGAPDH is similar to that from other trematodes and the predicted structure shows high similarity to those from other animals including the mammalian hosts. FhGAPDH lacks a binding pocket which has been exploited in the design of novel antitrypanosomal compounds. The protein can be expressed in, and purified from Escherichia coli; the recombinant protein was active and showed no cooperativity towards glyceraldehyde 3-phosphate as a substrate. In the absence of ligands, FhGAPDH was a mixture of homodimers and tetramers, as judged by protein-protein crosslinking and analytical gel filtration. The addition of either NAD(+) or glyceraldehyde 3-phosphate shifted this equilibrium towards a compact dimer. Thermal scanning fluorimetry demonstrated that this form was considerably more stable than the unliganded one. These responses to ligand binding differ from those seen in mammalian enzymes. These differences could be exploited in the discovery of reagents which selectively disrupt the function of FhGAPDH.
Biochimica et Biophysica Acta (BBA) - Proteins & Proteomics 04/2014;
[Show abstract][Hide abstract] ABSTRACT: Oxidation of NADH in the mitochondrial matrix of aerobic cells is catalysed by mitochondrial complex I. The regulation of this mitochondrial enzyme is not completely understood. An interesting characteristic of complex I from some organisms is the ability to adopt two distinct states: the so-called catalytically active (A) and the de-active, dormant state (D). The A-form in situ can undergo de-activation when the activity of the respiratory chain is limited (i.e. in the absence of oxygen). The mechanisms and driving force behind the A/D transition of the enzyme are currently unknown, but several subunits are most likely involved in the conformational rearrangements: the accessory subunit 39kDa (NDUFA9) and the mitochondrially encoded subunits, ND3 and ND1. These three subunits are located in the region of the quinone binding site. The A/D transition could represent an intrinsic mechanism which provides a fast response of the mitochondrial respiratory chain to oxygen deprivation. The physiological role of the accumulation of the D-form in anoxia is most probably to protect mitochondria from ROS generation due to the rapid burst of respiration following reoxygenation. The de-activation rate varies in different tissues and can be modulated by the temperature, the presence of free fatty acids and divalent cations, the NAD(+)/NADH ratio in the matrix, the presence of nitric oxide and oxygen availability. Cysteine-39 of the ND3 subunit, exposed in the D-form, is susceptible to covalent modification by nitrosothiols, ROS and RNS. The D-form in situ could react with natural effectors in mitochondria or with pharmacological agents. Therefore the modulation of the re-activation rate of complex I could be a way to ameliorate the ischaemia/reperfusion damage. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference. Guest Editors: Manuela Pereira and Miguel Teixeira.
[Show abstract][Hide abstract] ABSTRACT: Animal communication plays a crucial role in many species, and it involves a sender producing a signal and a receiver responding to that signal. The shape of a signal is determined by selection pressures acting upon it. One factor that exerts selection on acoustic signals is the acoustic environment through which the signal is transmitted. Recent experimental studies clearly show that senders adjust their signals in response to increased levels of anthropogenic noise. However, to understand how noise affects the whole process of communication, it is vital to know how noise affects the receiver's response during vocal interactions. Therefore, we experimentally manipulated ambient noise levels to expose male European robins (Erithacus rubecula) to two playback treatments consisting of the same song: one with noise and another one without noise. We found that males responding to a conspecific in a noise polluted environment increased minimum frequency and decreased song complexity and song duration. Thus, we show that the whole process of communication is affected by noise, not just the behaviour of the sender.
[Show abstract][Hide abstract] ABSTRACT: We have shown that Fasciola hepatica expresses at least six β-tubulins in the adult stage of its life cycle, designated F.hep-β-tub1-6 (Ryan et al., 2008). Here we show that different complements of tubulin isotypes are expressed in different tissues and at different life cycle stages; this information may inform the search for novel anthelmintics. The predominant (as judged by quantitative PCR) isotype transcribed at the adult stage was F.hep-β-tub1 and immunolocalisation studies revealed that this isotype occurred mainly in mature spermatozoa and vitelline follicles. Quantitative PCR indicated that changes occurred in the transcription levels of β-tubulin isotypes at certain life cycle stages and may be of importance in the efficacy of benzimidazole-based anthelmintic drugs, but there were no significant differences between the triclabendazole (TCBZ)-susceptible Leon isolate and the TCBZ-resistant Oberon isolate in the transcription levels of each of the isotypes. When three well-characterised isolates with differing susceptibilities to TCBZ were compared, only one amino acid change resulting from a homozygous coding sequence difference (Gly269Ser) in isotype 4 was observed. However, this change was not predicted to alter the overall structure of the protein. In conclusion, these findings indicate that there is tissue-specific expression of tubulin isotypes in the liver fluke but the development of resistance to TCBZ is not associated with changes in its presumed target molecule.
[Show abstract][Hide abstract] ABSTRACT: Chicken astroviruses (CAstVs) have been characterized recently. Due to their relatively poor growth in cell culture, virus-specific antigens are not readily available for the development of diagnostic reagents and vaccines. For this purpose two capsid protein antigens, specified by the 11672 isolate of CAstV, were produced in insect cells following infection with recombinant baculoviruses. The GST-11672 capsid protein, a fusion protein comprising the capsid protein and glutathione-S-transferase (GST) as an N-terminal affinity tag, and the 11672 capsid protein alone were detected by western blotting as proteins of ~100 and 70 kDa, respectively. Immunization with the affinity-purified GST-11672 capsid protein produced a polyclonal rabbit antiserum, which reacted by indirect immunofluorescence with Group B CAstVs but which showed no reactivity with the Group A CAstV isolate, 612. When used as part of an immunoperoxidase-based immunohistochemical procedure, this rabbit antiserum facilitated the detection of CAstV antigen in formalin-fixed, paraffin-embedded kidney tissue at the sites of histopathology characteristic of nephritis. Although further evaluation with sera from commercial chickens is required, a prototype indirect antibody-detecting enzyme-linked immunosorbent assay (ELISA) based on affinity-purified GST-11672 capsid protein as coating antigen demonstrated considerable potential with low ELISA absorbance values being generated with sera from specific pathogen free (SPF) chickens, and high absorbance values being generated with serum samples from experimentally infected chickens. Immunization experiments of SPF chickens showed that, when administered as mixtures with oil adjuvant, crude cell lysates containing the GST-11672 capsid protein or the 11672 capsid protein elicited virus-specific antibody responses that were detectable by indirect immunofluorescence and by virus neutralization assays.
[Show abstract][Hide abstract] ABSTRACT: The unique feature of mitochondrial complex I is the so-called A/D transition (active-deactive transition). The A-form catalyses rapid oxidation of NADH by ubiquinone (k ~104 min-1) and spontaneously converts into the D-form if the enzyme is idle at physiological temperatures. Such deactivation occurs in vitro in the absence of substrates or in vivo during ischaemia, when the ubiquinone pool is reduced. The D-form can undergo reactivation given both NADH and ubiquinone availability during slow (k ~1-10 min-1) catalytic turnover(s). We examined known conformational differences between the two forms and suggested a mechanism exerting A/D transition of the enzyme. In addition, we discuss the physiological role of maintaining the enzyme in the D-form during the ischaemic period. Accumulation of the D-form of the enzyme would prevent reverse electron transfer from ubiquinol to FMN which could lead to superoxide anion generation. Deactivation would also decrease the initial burst of respiration after oxygen reintroduction. Therefore the A/D transition could be an intrinsic protective mechanism for lessening oxidative damage during the early phase of reoxygenation. Exposure of Cys39 of mitochondrially encoded subunit ND3 makes the D-form susceptible for modification by reactive oxygen species and nitric oxide metabolites which arrests the reactivation of the D-form and inhibits the enzyme. The nature of thiol modification defines deactivation reversibility, the reactivation timescale, the status of mitochondrial bioenergetics and therefore the degree of recovery of the ischaemic tissues after reoxygenation.
Biochemical Society Transactions 10/2013; 41(5):1325-30.
[Show abstract][Hide abstract] ABSTRACT: A size and trait-based marine community model was used to investigate interactions, with potential implications for yields, when a fishery targeting forage fish species (whose main adult diet is zooplankton) co-occurs with a fishery targeting larger-sized predator species. Predicted effects on the size structure of the fish community, growth and recruitment of fishes, and yield from the fisheries were used to identify management trade-offs among the different fisheries. Results showed that moderate fishing on forage fishes imposed only small effects on predator fisheries, whereas predator fisheries could enhance yield from forage fisheries under some circumstances.
[Show abstract][Hide abstract] ABSTRACT: A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Sligo TCBZ-resistant fluke isolate was used for these experiments and the Pgp inhibitor selected was R(+)-verapamil [R(+)-VPL]. In the first experiment, flukes were initially incubated for 2 h in R(+)-VPL (1x10(-4) M), then incubated in R(+)-VPL + triclabendazole sulphoxide (TCBZ.SO) (50 μg/ml) until flukes ceased movement (at 9 h post-treatment). In a second experiment, flukes were incubated in TCBZ.SO alone and removed from the incubation medium following cessation of motility (after 15 h). In the third experiment, flukes were incubated for 24 h in R(+)-VPL on its own. Changes to the tegumental system and gut following drug treatment and following Pgp inhibition were assessed by means of light microscope histology and transmission electron microscopy. Incubation of the Sligo isolate in either R(+)-VPL or TCBZ.SO on their own had a limited impact on the tegumental syncytium and tegumental cells; the changes were consistent with a stress response by the fluke to drug action. Greater disruption was observed when the drugs were combined, in terms of the vacuolation and sloughing of the syncytium, spine disruption and the cessation of secretory activity in, and degradation of, the tegumental cells. In the gut, treatment with R(+)-VPL on its own did not lead to any cellular changes. Some limited changes to the mitochondria and the granular endoplasmic reticulum were observed after incubation in TCBZ.SO alone, together with reduced secretory activity and evidence of autophagy. However, these changes were far more pronounced in combination-treated flukes. The results of this study support the concept of altered drug efflux in TCBZ-resistant flukes and indicate that drug transporters may play a role in the development of drug resistance.
[Show abstract][Hide abstract] ABSTRACT: The glycolytic enzyme triose phosphate isomerase from Schistosoma mansoni is a potential target for drugs and vaccines. Molecular modelling of the enzyme predicted that a Ser-Ala-Asp motif which is believed to be a helminth-specific epitope is exposed. The enzyme is dimeric (as judged by gel filtration and cross-linking), resistant to proteolysis and highly stable to thermal denaturation (melting temperature of 82.0 °C). The steady-state kinetic parameters are high (Km for dihydroxyacetone phosphate is 0.51 mM; Km for glyceraldehyde 3-phosphate is 1.1 mM; kcat for dihydroxyacetone phosphate is 7800 s(-1) and kcat for glyceraldehyde 3-phosphate is 6.9 s(-1)).
FEBS letters 09/2013;
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