The N-terminal Helix Controls the Transition between the Soluble and Amyloid States of an FF Domain

Background

Protein aggregation is linked to the onset of an increasing number of human nonneuropathic (either localized or systemic) and neurodegenerative disorders. In particular, misfolding of native α-helical structures and their self-assembly into nonnative intermolecular β-sheets has been proposed to trigger amyloid fibril formation in Alzheimer’s and Parkinson’s diseases.

Methods

Here, we use a battery of biophysical techniques to elucidate the conformational conversion of native α-helices into amyloid fibrils using an all-α FF domain as a model system.

Results

We show that under mild denaturing conditions at low pH this FF domain self-assembles into amyloid fibrils. Theoretical and experimental dissection of the secondary structure elements in this domain indicates that the helix 1 at the N-terminus has both the highest α-helical and amyloid propensities, controlling the transition between soluble and aggregated states of the protein.

Conclusions

The data illustrates the overlap between the propensity to form native α-helices and amyloid structures in protein segments.

Significance

The results presented contribute to explain why proteins cannot avoid the presence of aggregation-prone regions and indeed use stable α-helices as a strategy to neutralize such potentially deleterious stretches.     

Visual Cues Given by Humans Are Not Sufficient for Asian Elephants (Elephas maximus) to Find Hidden Food

Recent research suggests that domesticated species – due to artificial selection by humans for specific, preferred behavioral traits – are better than wild animals at responding to visual cues given by humans about the location of hidden food. \Although this seems to be supported by studies on a range of domesticated (including dogs, goats and horses) and wild (including wolves and chimpanzees) animals, there is also evidence that exposure to humans positively influences the ability of both wild and domesticated animals to follow these same cues. Here, we test the performance of Asian elephants (Elephas maximus) on an object choice task that provides them with visual-only cues given by humans about the location of hidden food. Captive elephants are interesting candidates for investigating how both domestication and human exposure may impact cue-following as they represent a non-domesticated species with almost constant human interaction. As a group, the elephants (n = 7) in our study were unable to follow pointing, body orientation or a combination of both as honest signals of food location. They were, however, able to follow vocal commands with which they were already familiar in a novel context, suggesting the elephants are able to follow cues if they are sufficiently salient. Although the elephants’ inability to follow the visual cues provides partial support for the domestication hypothesis, an alternative explanation is that elephants may rely more heavily on other sensory modalities, specifically olfaction and audition. Further research will be needed to rule out this alternative explanation.     

Urogenital Epithelial Cells as Simple Markers of Estrogen Response in Infants: Methods and Applications

Exposure to estrogen-mimicking chemicals during critical periods of development, such as infancy, may have adverse effects. However, these effects can be difficult to characterize in most epidemiologic studies. For example, growth of reproductive organs may be susceptible to estrogenic chemicals, but measuring it requires skilled ultrasound examination; timing of pubertal onset may be altered, but observing it requires long-term follow up. To address the need for a simple marker of response to estrogenic exposures in infants, we propose a novel application of a classic marker of estrogen response in adult women: cytological evaluation of urogenital epithelial cells. In this cross-sectional study of 34 female and 41 male infants, we demonstrate that epithelial cells can be obtained from swabs of the vaginal introitus (females) and urethral meatus (males), as well as from spun urine, and that these cells respond to differential estrogenic conditions, as indicated by the relative abundance of the superficial epithelial cell type. To model varying estrogen exposure, we sampled from infants who were either newborn (highly exposed to maternal estrogens), or 12 weeks old (12W) (negligibly exposed to estrogen). Newborns had a higher percentage of superficial cells (%S), as compared to 12W (mean ± standard error: 8.3 ± 1.8 vs. 0.9 ± 0.2) (p < 0.01), consistent with an estrogen response. This difference in %S from newborn to 12W was observed similarly for swab (-7.6 ± 1.7) and urine (-7.3 ± 2.6) specimens and for males (-9.6 ± 2.9) and females (-5.2 ± 2.1). Examination of urogenital epithelial cells can successfully demonstrate estrogen response in both sexes, using cell specimens collected from either swab or urine sampling. In future studies, this simple, non-invasive method may be applied to assess whether estrogen-mimicking chemicals produce an estrogenic response in infants.     

Programmable assembly of 2D crystalline protein arrays into covalently stacked 3D bionanomaterials

Rational embellishment of self-assembling two-dimensional (2D) proteins make it possible to build 3D nanomaterials with novel catalytic, optoelectronic and mechanical properties. However, introducing multiple sites of embellishment into 2D protein arrays without affecting the self-assembly is challenging, limiting the ability to program in additional functionality and new 3D configurations. Here we introduce two orthogonal covalent linkages at multiple sites in a 2D crystalline-forming protein without affecting its self-assembly. We first engineered the surface-layer protein SbsB from Geobacillus stearothermophilus pV72/p2 to display isopeptide bond-forming protein conjugation pairs, SpyTag or SnoopTag, at four positions spaced 5.7-10.5 nm apart laterally and 3 nm axially. The C-terminal and two newly-identified locations within SbsB monomer accommodated the short SpyTag or SnoopTag peptide tags without affecting the 2D lattice structure. Introducing tags at distinct locations enabled orthogonal and covalent binding of SpyCatcher- or SnoopCatcher-protein fusions to micron-sized 2D nanosheets. By introducing different types of bifunctional cross-linkers, the dual-functionalized nanosheets were programmed to self-assemble into different 3D stacks, all of which retain their nanoscale order. Thus, our work creates a modular protein platform that is easy to program to create dual-functionalized 2D and lamellar 3D nanomaterials with new catalytic, optoelectronic, and mechanical properties.     

Amyloid precursor protein is a restriction factor that protects against Zika virus infection in mammalian brains

Zika virus (ZIKV) is a neurotropic flavivirus that causes several diseases including birth defects such as microcephaly. Intrinsic immunity is known to be a frontline defense against viruses through host anti-viral restriction factors. Limited knowledge is available on intrinsic immunity against ZIKV in brains. Amyloid precursor protein (APP) is predominantly expressed in brains and implicated in the pathogenesis of Alzheimer''s diseases. We have found that ZIKV interacts with APP, and viral infection increases APP expression via enhancing protein stability. Moreover, we identified the viral peptide, HGSQHSGMIVNDTGHETDENRAKVEITPNSPRAEATLGGFGSLGL, which is capable of en-hancing APP expression. We observed that aging brain tissues with APP had protective effects on ZIKV infection by reducing the availability of the viruses. Also, knockdown of APP expression or blocking ZIKV-APP interactions enhanced ZIKV replication in human neural progenitor/stem cells. Finally, intracranial infection of ZIKV in APP-null neonatal mice resulted in higher mortality and viral yields. Taken together, these findings suggest that APP is a restriction factor that protects against ZIKV by serving as a decoy receptor, and plays a protective role in ZIKV-mediated brain injuries.     

The flavonoid chrysin attenuates colorectal pathological remodeling reducing the number and severity of pre-neoplastic lesions in rats exposed to the carcinogen 1,2-dimethylhydrazine

Phenolic compounds are naturally occurring, bioactive substances with marked antioxidant and anti-inflammatory potential. The flavonoid chrysin, found in high levels in honey bee propolis, inhibits the activity of enzymes involved in carcinogenesis. We have investigated the effect of chrysin on pre-neoplastic colorectal lesions (ACF, aberrant crypt foci) in a rat model of chemical carcinogenesis induced by 1,2-dimethylhydrazine (DMH). Female Wistar rats weighing 137.2?±?24.3 g received weekly one subcutaneous injection of DMH (20 mg/kg) for 10 weeks. The animals were divided into five groups each with seven animals: Group 1, 0.9% saline; Group 2, DMH+0.9% saline; Group 3, DMH+chrysin (10 mg/kg); Group 4, DMH+chrysin (100 mg/kg); Group 5, DMH+chrysin (200 mg/kg). Groups 2 and 3 showed a significant increase in ACF number, nucleolus organizer regions per enterocyte nucleus and nitrite/nitrate serum levels compared with Group 1. Groups 4 and 5 presented a significant reduction in all these parameters compared with Group 2. The levels of antioxidant minerals (copper, magnesium, selenium, zinc) and the number of enteroendocrine and mucin-producing cells were significantly reduced in Groups 2 and 3 but were similar in Groups 4 and 5 compared with Group 1. Chrysin, at 100 mg/kg and 200 mg/kg, was effective in attenuating pathological colorectal remodeling, reducing the number of pre-neoplastic lesions in rats exposed to DMH. Some of these effects might be attributable to the recovery of antioxidant mineral levels, a reduction in systemic nitrosative stress and an inhibition of the cellular proliferation induced by this flavonoid.     

Differential proliferation rates generate patterns of mechanical tension that orient tissue growth

Orientation of cell divisions is a key mechanism of tissue morphogenesis. In the growing Drosophila wing imaginal disc epithelium, most of the cell divisions in the central wing pouch are oriented along the proximal–distal (P–D) axis by the Dachsous‐Fat‐Dachs planar polarity pathway. However, cells at the periphery of the wing pouch instead tend to orient their divisions perpendicular to the P–D axis despite strong Dachs polarization. Here, we show that these circumferential divisions are oriented by circumferential mechanical forces that influence cell shapes and thus orient the mitotic spindle. We propose that this circumferential pattern of force is not generated locally by polarized constriction of individual epithelial cells. Instead, these forces emerge as a global tension pattern that appears to originate from differential rates of cell proliferation within the wing pouch. Accordingly, we show that localized overgrowth is sufficient to induce neighbouring cell stretching and reorientation of cell division. Our results suggest that patterned rates of cell proliferation can influence tissue mechanics and thus determine the orientation of cell divisions and tissue shape.     

Reconstruction of the cranial musculature and masticatory function of the Pleistocene panamerican ground sloth Eremotherium laurillardi (Mammalia,Xenarthra, Megatheriidae)

Cranial musculature, dental function and mandibular movement patterns in Eremotherium laurillardi were reconstructed from the examination of crania and dentitions. Size, shape and pattern of muscle divisions were reconstructed from the examination of bony rugosities indicating muscle attachments. Details of masticatory muscle structure and function were based on dissections of the tree sloths Bradypus and Choloepus. Among sloths, masticatory muscles in E. laurillardi demonstrate a different synergist–antagonist pattern, reflecting greater emphasis on mediolateral mandibular movements. Eight cranial character complexes (anterior facial, zygomatic arch, superficial masseter, deep masseter–zygomaticomandibularis, pterygoid, temporal, occipital and occlusal) determined by interrelated contributions of each component made to group functions were identified. An elongate anterior face and predental spout in E. laurillardi allowed protrusion of a long narrow tongue at small degrees of gape, reflecting a probably ancestral xenarthran condition. Gape minimisation, in conjunction with the mediolaterally directed masticatory stroke in E. laurillardi, was a unique solution to increase masticatory efficiency by permitting molariform tooth shearing surfaces to remain in or near occlusion for a greater percentage of each chewing cycle.     

Ultrastructural and Biogeochemical Features of Microbiotic Soil Crusts and their Implications in a Semi-Arid Habitat

This investigation was designed to explore the relationships between lichen symbionts (phycobiont and mycobiont) and the substrate on which they grow by examining the chemical and ultrastructural features of the lichen-soil interface. These lichens form an integral part of microbiotic soil crusts. Fragments of three different lichen biotypes growing over gypsum crystals and marls were fixed and embedded in resin. The lichen-substratum interface was then examined by scanning electron microscopy with backscattered electron imaging. In situ observation, microanalytical (EDS), and FT-Raman plus infrared spectroscopy of the lichen-substratum interface indicated that different ultrastructural features of the mycobiont were related to biogeochemical processes and Ca 2+ distribution in the soil crust. Phycobionts were observed to make direct contact with the substratum and to be surrounded by a nondifferentiated thallus structure. These observations suggest that they can grow outside the thallus in the early stages of lichen development in the semi-arid conditions of their habitat. The particular ultrastructural features of the lichen thallus and of the lichen-substratum interface appear to have marked effects on runoff phenomena and ponding generation of the surface.     

Fossilization of Acidophilic Microorganisms

This study examines fossil microorganisms found in iron-rich deposits in an extreme acidic environment, the Tinto River in SW Spain. Both electron microscopy (SEM and TEM) and non-destructive in situ microanalytical techniques (EDS, EMP and XPS) were used to determine the role of permineralization and encrustation in preserving microorganisms forming biofilms in the sediments. Unicellular algae were preserved by silica permineralization of their cell walls. Bacterial biofilms were preserved as molds by epicellular deposition of schwertmannite around them. In the case of fungi and filamentous algae, we observed permineralization of cell structures by schwertmannite in the sediments. The extracellular polymeric matrix around the cells was also preserved through permineralization of the fibrillar component. The process of permineralization and deposition of iron-rich precipitates present in the acidic waters of Rio Tinto served to preserve many microfossils in an oxidizing environment, in which organic compounds would not normally be expected to persist. Studies of microbial fossil formation mechanisms in modern extreme environments should focus on defining criteria to identify inorganic traces of microbial life in past environments on Earth or other planets.