Structural and biochemical insights into 7β‐hydroxysteroid dehydrogenase stereoselectivity

Hydroxysteroid dehydrogenases are of great interest as biocatalysts for transformations involving steroid substrates. They feature a high degree of stereo‐ and regio‐selectivity, acting on a defined atom with a specific configuration of the steroid nucleus. The crystal structure of 7β‐hydroxysteroid dehydrogenase from Collinsella aerofaciens reveals a loop gating active‐site accessibility, the bases of the specificity for NADP⁺, and the general architecture of the steroid binding site. Comparison with 7α‐hydroxysteroid dehydrogenase provides a rationale for the opposite stereoselectivity. The presence of a C‐terminal extension reshapes the substrate site of the β‐selective enzyme, possibly leading to an inverted orientation of the bound substrate. Proteins 2016; 84:859–865. © 2016 Wiley Periodicals, Inc.     

Liver size and lipid content differences between BALB/c and BALB/cJ mice on a high-fat diet are due,in part,to Zhx2

Mammalian Genome - BALB/cJ mice exhibit considerable phenotypic differences with other BALB/c substrains. Some of these traits involve the liver, including persistent postnatal expression of genes...     

ALS-Linked Mutations Affect UBQLN2 Oligomerization and Phase Separation in a Position- and Amino Acid-Dependent Manner

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Lianas as a food resource for herbivorous insects: a comparison with trees

Woody climbers or, ‘lianas’, are one of the features that characterise rainforests. They contribute substantially to plant diversity and leaf biomass which makes them a potentially important food source for herbivores. Here, we focus on insect herbivores, folivores in particular, to show how disparities in the quantitative and qualitative availability of leaves between lianas and trees may differentially influence insect folivory and the herbivore communities themselves. We develop a conceptual model and show that lianas in general have lower structural and chemical defences, a greater nutritional profile and a preferable phenology in comparison with trees, which, contrary to our expectations, has led to assemblages of more‐specialised insects. The impacts this has on higher trophic levels and broader ecological networks, however, are poorly known. We show through a study of four tropical floras from different biogeographic realms that lianas are likely to be a target for a wide range of insect herbivore taxa as they are a phylogenetically diverse group and increase diversity of higher taxa at local scales. This, in combination with their highly palatable leaves, may also make them a suitable temporary food source for insects during times when preferred host plants are scarce. This phenomenon has been observed in mammalian herbivores but awaits investigation in insects as does the effects this may have on survival and fitness. Apparent recent increases in liana abundances in some forests, likely due to climate change, makes understanding their role in supporting and maintaining biodiversity an increasingly important and necessary challenge. Since trees or saplings have usually been the subject of studies on insect herbivory, major knowledge gaps remain about the ways in which lianas contribute to, support and maintain the ecosystems in which they exist. We use our conceptual model to guide future research directions and express the necessity for caution when extrapolating explanations of herbivory derived from data on trees to growth forms with fundamentally different ecologies.     

Validation of an OpenSim full-body model with detailed lumbar spine for estimating lower lumbar spine loads during symmetric and asymmetric lifting tasks

There is currently no validated full-body lifting model publicly available on the OpenSim modelling platform to estimate spinal loads during lifting. In this study, the existing full-body-lumbar-spine model was adapted and validated for lifting motions to produce the lifting full-body model. Back muscle activations predicted by the model closely matched the measured erector spinae activation patterns. Model estimates of intradiscal pressures and in vivo measurements were strongly correlated. The same spine loading trends were observed for model estimates and reported vertebral body implant measurements. These results demonstrate the suitability of this model to evaluate changes in lumbar loading during lifting.     

Anaerobic fungal communities differ along the horse digestive tract

Anaerobic fungi are potent fibre degrading microbes in the equine hindgut, yet our understanding of their diversity and community structure is limited to date. In this preliminary work, using a clone library approach we studied the diversity of anaerobic fungi along six segments of the horse hindgut: caecum, right ventral colon (RVC), left ventral colon (LVC), left dorsal colon (LDC), right dorsal colon (RDC) and rectum. Of the 647 ITS1 clones, 61.7 % were assigned to genus level groups that are so far without any cultured representatives, and 38.0 % were assigned to the cultivated genera Neocallimastix (35.1 %), Orpinomyces (2.3 %), and Anaeromyces (0.6 %). AL1 dominated the group of uncultured anaerobic fungi, particularly in the RVC (88 %) and LDC (97 %). Sequences from the LSU clone library analysis of the LDC, however, split into two distinct phylogenetic clusters with low sequence identity to Caecomyces sp. (94–96 %) and Liebetanzomyces sp. (92 %) respectively. Sequences belonging to cultured Neocallimastix spp. dominated in LVC (81 %) and rectum (75.5 %). Quantification of anaerobic fungi showed significantly higher concentrations in RVC and RDC compared to other segments, which influenced the interpretation of the changes in anaerobic fungal diversity along the horse hindgut. These preliminary findings require further investigation.     

Epidermal hyperplasia and expansion of the interfollicular stem cell compartment in mutant mice with a C-terminal truncation of Patched1

Hedgehog (Hh) signaling is conserved from flies to humans and is indispensable in embryogenesis and adulthood. Patched (Ptc) encodes a receptor for Hh ligands and functions as a tumor suppressor. PTCH1 mutations in humans are found in basal cell carcinoma (BCC) and irradiated Ptc1(+/-) mice recapitulate this phenotype. However, due to embryonic lethality associated with the Ptc1 null mutation, its normal function in embryonic and adult skin remains unknown. Here we describe the epidermal phenotypes of a spontaneous and viable allele of Ptc1, Ptc1(mes), in which the C-terminal domain (CTD) is truncated. Ptc1(mes/mes) embryos display normal epidermal and hair follicle development. Postnatal Ptc1(mes/mes) skin displays severe basal cell layer hyperplasia and increased proliferation, while stratification of the suprabasal layers is mostly normal. Interestingly, truncation of the Ptc1 CTD did not result in skin tumors. However, long term labeling studies revealed a greater than three-fold increase in label-retaining cells in the interfollicular epidermis of Ptc1(mes/mes) adults, indicating possible expansion of the epidermal stem cell compartment. Increased expression of regulators of epidermal homeostasis, c-Myc and p63, was also observed in Ptc1(mes/mes) adult skin. These results suggest that the CTD of Ptc1 is involved in regulating epidermal homeostasis in mature skin.     

Natural genetic variation in cuticular hydrocarbon expression in male and female Drosophila melanogaster

Cuticular hydrocarbons (CHCs) act as contact pheromones in Drosophila melanogaster and are an important component of several ecological traits. Segregating genetic variation in the expression of CHCs at the population level in D. melanogaster is likely to be important for mate choice and climatic adaptation; however, this variation has never been characterized. Using a panel of recombinant inbred lines (RILs) derived from a natural population, we found significant between-line variation for nearly all CHCs in both sexes. We identified 25 QTL in females and 15 QTL in males that pleiotropically influence CHC expression. There was no evidence of colocalization of QTL for homologous traits across the sexes, indicating that sexual dimorphism and low intersex genetic correlations between homologous CHCs are a consequence of largely independent genetic control. This is consistent with a pattern of divergent sexual and natural selection between the sexes.     

Alterations in linker flexibility suppress DNA topoisomerase I mutant-induced cell lethality

Eukaryotic DNA topoisomerase I (Top1p) catalyzes changes in DNA topology via the formation of a covalent enzyme-DNA intermediate, which is reversibly stabilized by the anticancer agent camptothecin (CPT). Crystallographic studies of the 70-kDa C terminus of human Top1p bound to duplex DNA describe a monomeric protein clamp circumscribing the DNA helix. The structures, which lack the N-terminal domain, comprise the conserved clamp, an extended linker domain, and the conserved C-terminal active site Tyr domain. CPT bound to the covalent Top1p-DNA complex limits linker flexibility, allowing structural determination of this domain. We previously reported that mutation of Ala(653) to Pro in the linker increases the rate of enzyme-catalyzed DNA religation, thereby rendering Top1A653Pp resistant to CPT (Fiorani, P., Bruselles, A., Falconi, M., Chillemi, G., Desideri, A., and Benedetti P. (2003) J. Biol. Chem. 278, 43268-43275). Molecular dynamics studies suggested mutation-induced increases in linker flexibility alter Top1p catalyzed DNA religation. To address the functional consequences of linker flexibility on enzyme catalysis and drug sensitivity, we investigated the interactions of the A653P linker mutation with a self-poisoning T718A mutation within the active site of Top1p. The A653P mutation suppressed the lethal phenotype of Top1T718Ap in yeast, yet did not restore enzyme sensitivity to CPT. However, the specific activity of the double mutant was decreased in vivo and in vitro, consistent with a decrease in DNA binding. These findings support a model where changes in the flexibility or orientation of the linker alter the geometry of the active site and thereby the kinetics of DNA cleavage/religation catalyzed by Top1p.