X-ray structure of recombinant horse L-chain apoferritin at 2.0 Å resolution: implications for stability and function

The X-ray structure of recombinant horse L-chain (rL) apoferritin, solved at 2.0?Å resolution with a final R factor of 17.9%, gives evidence that the residue at position 93 in the sequence is a proline and not a leucine, as found in earlier sequencing studies. The structure is isomorphous with other apoferritin structures, and we thus draw particular attention to those structural features which can be related to the stability and function of the protein. Analysis of hydrogen bonding and salt bridge interactions shows that dimers and tetramers are the most stable molecular entities within the protein shell: a result confirming earlier biophysical experiments. The stability of horse rL apoferritin to both dissociation into subunits at acidic pH values and to complete unfolding in guanidine chloride solutions is compared with that of other apoferritins. This emphasizes the role played by the salt bridge in the stability of this protein family. The horse rL apoferritin is significantly more resistant to denaturation than horse spleen ferritin, which in turn is more resistant than any human rH apoferritins, even those for which a salt bridge is restored. Finally, this structure determination not only establishes that a preformed pocket exists in L-chain apoferritin, at a site known to be able to bind porphyrin, but also underlines the particular function of a cluster of glutamic acids (E53, E56, E57 and E60) located at the entrance of this porphyrin-binding pocket.     

Distinct subcellular localization of β-tubulin epitopes in the adult mouse brain

 A panel of monoclonal antibodies specific of α-tubulin (TU-01, TU-09) and β-tubulin (TU-06, TU-13) subunits was used to study the location of N-terminal structural domains of tubulin in adult mouse brain. The specificity of antibodies was confirmed b immunoblotting experiments. Immunohistochemical staining of vibratome sections from cerebral cortex, cerebellum, hippocampus, and corpus callosum showed that antibodies TU-01, TU-09, and TU13 reacted with neuronal and glial cells and their processes, whereas the TU-06 antibody stained only the perikarya. Dendrites and axons were either unstained or their staining was very weak. As the TU-06 epitope is located on the N-terminal structural domain of β-tubulin, the observed staining pattern cannot be interpreted as evidence of a distinct subcellular localization of β-tubulin isotypes or known post-translational modifications. The limited distribution of the epitope could, rather, reflect differences between the conformations of tubulin molecules in microtubules of somata and neurites or, alternatively, a specific masking of the corresponding region on the N-terminal domain of β-tubulin by interacting protein(s) in dendrites and axons. Accepted: 11 November 1996     

Simple and non-radioactive method for determination of sialyltransferase activity

A new, non-radioactive and cheap colorimetric method for determination of activity of sialyltransferases of various specifities using natural substrates based on 2-thiobarbituric acid assay is presented. The assay was tested with three different sialyltransferases (a-2,3 and a-2,6) and compared with the radioactive assay.     

DDT (dicophane) and postmenopausal breast cancer in Europe: case-control study.

OBJECTIVE: To examine any possible links between exposure to DDE (1,1-dichloro-2,2-bis (p-chlorophenyl)ethylene), the persistent metabolite of the pesticide dicophane (DDT), and breast cancer. DESIGN: Multicentre study of exposure to DDE by measurement of adipose tissue aspirated from the buttocks. Laboratory measurements were conducted in a single laboratory. Additional data on risk factors for breast cancer were obtained by standard questionnaires. SETTING: Centres in Germany, the Netherlands, Northern Ireland, Switzerland, and Spain. SUBJECTS: 265 postmenopausal women with breast cancer and 341 controls matched for age and centre. MAIN OUTCOME MEASURE: Adipose DDE concentrations. RESULTS: Women with breast cancer had adipose DDE concentrations 9.2% lower than control women. No increased risk of breast cancer was found at higher concentrations. The odds ratio of breast cancer, adjusted for age and centre, for the highest versus the lowest fourth of DDE distribution was 0.73 (95% confidence interval 0.44 to 1.21) and decreased to 0.48 (0.25 to 0.95; P for trend = 0.02) after adjustment for body mass index, age at first birth, and current alcohol drinking. Adjustment for other risk factors did not materially affect these estimates. CONCLUSIONS: The lower DDE concentrations observed among the women with breast cancer may be secondary to disease inception. This study does not support the hypothesis that DDE increases risk of breast cancer in postmenopausal women in Europe.     

Arthropod biodiversity loss and the transformation of a tropical agro-ecosystem

The coffee (Coffea arabica) agro-ecosystem in the Central Valley of Costa Rica was formerly characterized by a high vegetational diversity. This complex system has been undergoing a major transformation to capital-intensive monocultural plantations where all shade trees are eliminated. In this study we examined the pattern of arthropod biodiversity loss associated with this transformation. Canopy arthropods were sampled in three coffee farms: a traditional plantation with many species of shade trees, a moderately shaded plantation with only Erythrina poeppigeana and coffee, and a coffee monoculture. An insecticidal fogging technique was used to sample both canopy and coffee arthropods. Data are presented on three major taxonomic groups: Coleoptera, non-formicid Hymenoptera, and Formicidae. Data demonstrate that the transformation of the coffee agro-ecosystem results in a significant loss of biological diversity of both canopy arthropods as well as arthropods living in coffee bushes. Percentage of species overlap was very small for all comparisons. Furthermore, species' richness on a per tree basis was found to be within the same order of magnitude as that reported for trees in tropical forests. If results presented here are generalizable, this means that conservation efforts to preserve biological diversity should also include traditional agro-ecosystems as conservation units.     

Hydrological cycle and interannual variability of the aquatic community in a temporary saline lake (Fuente de Piedra,Southern Spain)

Fuente de Piedra is a shallow, temporary saline lake whoseseasonal behavior is strongly dependent on the annual hydrologicalbudget. In this study, we outline the characteristics of Fuente dePiedra Lake for two years that had different hydrological budgets.The high precipitations in 1989–90 caused the lake not to dry asusual, and decreased both salinity and the amplitude of changes.There were also differences in nutrient dynamics, with generallylower concentrations of soluble reactive phosphorus and ammonium,whereas in the more humid year nitrate showed a distinct maximum inwinter. Winter bloom chlorophyll a concentrations were alsomuch higher in 1989–90 (>600 g l-1) but there wasalso a winter productive phase that was presumably poorly coupledwith consumption processes that predominate in spring. Planktonicassemblages were different between years. Highly halotolerantphytoplankton species (Dunaliella salina and D. viridis) became scarcer, and especially two previouslyunrecorded diatoms (Cyclotella sp. and Chaetoceros sp.)became dominant in the bloom time in the wet year. The speciesrichness of the zooplankton increased in the wet year, with newspecies appearing that were not collected during 1987–88(Branchinectella media, Daphnia mediterranea, Macrothrix sp.,Arctodiaptomus salinus, Cyclops sp., Sigara sp...).There was also a much higher development of macrophytes (Ruppiadrepanensis, Althenia orientalis, Lamprothamnium papulosum)and bird populations, especially flamingoes (Phoenicopterusruber).Important interannual variations in this sort of system pointto the need for long term studies to observe the whole range ofstates that define the lake as an entity.     

Sarsicopia polaris gen. et sp.n., the first platycopioida (Copepoda: Crustacea) from the Arctic Ocean,and its phylogenetic significance

A new genus of Platycopioida is described from a boxcore sample taken at a depth of 534 m in the ArcticBarents Sea. This is the deepest record ofPlatycopioida so far. Sarsicopia gen. n. is thesistergroup of a taxon comprising Platycopia and Nanocopia; the sistergroup ofthese is Antrisocopia. Sarsicopia gen. n.is the only platycopioid to retain 2 inner setae onthe second endopod segment P2–P4, and 8 setae in thethird endopod segment of P2. The male antennnule isremarkable in having a geniculation located betweenancestral segments XX and XXI. It is suggested thatthis flexure zone was already present in thegroundpattern of Copepoda. Platycopia and Nanocopia have secondarily lost thisgeniculation.     

Effects of water level fluctuations on phytoplankton in a river-floodplain lake system (Paraná River,Argentina)

Several aspects of community organization wereanalyzed comparatively in a small side-arm of theParaná River (Correntoso) and a shallowfloodplain lake (El Tigre) (31° 41 S and60° 42 W), in relation to the hydrology of thesystem. Taxonomic and morphological composition inthe river differed from that in the lake: the riverhad lower species richness (151 vs 218),different contributions of some Classes to totalspecies number (higher Cyano-, Zygo- andDiatomophyceae vs higher Chlorophyceae), anddiffent proportions of nannoplanktonic algae (67.5%vs 80.7%) and netplanktonic filamentousspecies (18.2% vs 4.2%). Phytoplanktonbiomass, higher in the lake than in the river due tothe retention time, was mostly dominated bynannoplankton and netplankton. Loticphytoplankton was dominated by typical fluvialspecies of Diatomophyceae (R-strategists). Riverconditions seem to maintain a subclimacticcommunity, which was little impacted by the flushingof populations from floodplain lakes. Water levelwas the main factor controlling phytoplanktonbiomass, species diversity (H), evenness (E) andcommunity change rate () in the river. Inthe lake, phytoplankton had an autogenicsuccessional sequence during the isolation phase (C-to S-strategists) and other responses todisturbance, mainly during the flood(R-strategists). Frequent changes in phytoplanktoncomposition, biomass, H, E and , revealed aenvironmental instability in the lake, which may beexplained by interactions of external factors(hydrology and climatology) and those of internalorigin, such as nutrients and grazing.     

Contribution of Mutation and RNA Recombination to the Evolution of a Plant Pathogenic RNA

The nucleotide sequence of 17 variants of the satellite RNA of cucumber mosaic virus (CMV-satRNA) isolated from field-infected tomato plants in the springs of 1989, 1990, and 1991 was determined. The sequence of each of the 17 satRNAs was unique and was between 334 and 340 nucleotides in length; 57 positions were polymorphic. There was much genetic divergence, ranging from 0.006 to 0.141 nucleotide substitutions per site for pairwise comparisons, and averaging 0.074 for any pair. When the polymorphic positions were analyzed relative to a secondary structure model proposed for CMV-satRNAs, it was found that there were significantly different numbers of changes in base-paired and non–base-paired positions, and that mutations that did not disrupt base pairing were preferred at the putatively paired sites. This supports the concept that the need to maintain a functional structure may limit genetic divergence of CMV-satRNA. Phylogenetic analyses showed that the 17 CMV-satRNA variants clustered into two subgroups, I and II, and evolutionary lines proceeding by the sequential accumulation of mutations were apparent. Three satRNA variants were outliers for these two phylogenetic groups. They were shown to be recombinants of subgroup I and II satRNAs by calculating phylogenies for different molecular regions and by using Sawyer's test for gene conversion. At least two recombination events were required to produce these three recombinant satRNAs. Thus, recombinants were found to be frequent (∼17%) in natural populations of CMV-satRNA, and recombination may make an important contribution to the generation of new variants. To our knowledge this is the first report of data allowing the frequency of recombinant isolates in natural populations of an RNA replicon to be estimated. Received: 14 May 1996 / Accepted: 17 July 1996