Mutation in a flexible linker modulates binding affinity for modular complexes

Tandem beta zippers are modular complexes formed between repeated linear motifs and tandemly arrayed domains of partner proteins in which β-strands form upon binding. Studies of such complexes, formed by LIM domain proteins and linear motifs in their intrinsically disordered partners, revealed spacer regions between the linear motifs that are relatively flexible but may affect the overall orientation of the binding modules. We demonstrate that mutation of a solvent exposed side chain in the spacer region of an LHX4–ISL2 complex has no significant effect on the structure of the complex, but decreases binding affinity, apparently by increasing flexibility of the linker.     

Seroepidemiology of Crimean-Congo Haemorrhagic Fever among cattle in Cameroon: Implications from a One Health perspective

BackgroundCrimean-Congo Haemorrhagic Fever (CCHF) is a tick-borne viral zoonotic disease distributed across several continents and recognized as an ongoing health threat. In humans, the infection can progress to a severe disease with high fatality, raising public health concerns due to the limited prophylactic and therapeutic options available. Animal species, clinically unaffected by the virus, serve as viral reservoirs and amplifier hosts, and can be a valuable tool for surveillance. Little is known about the occurrence and prevalence of Crimean-Congo Haemorrhagic Fever Virus (CCHFV) in Cameroon. Knowledge on CCHFV exposure and the factors associated with its presence in sentinel species are a valuable resource to better understand transmission dynamics and assess local risks for zoonotic disease emergence.Methods and findingsWe conducted a CCHFV serological survey and risk factor analysis for animal level seropositivity in pastoral and dairy cattle in the North West Region (NWR) and the Vina Division (VD) of the Adamawa Region in Cameroon. Seroprevalence estimates were adjusted for sampling design-effects and test performance. In addition, explanatory multivariable logistic regression mixed-effects models were fit to estimate the effect of animal characteristics, husbandry practices, risk contacts and ecological features on the serological status of pastoral cattle. The overall seroprevalence was 56.0% (95% CI 53.5–58.6) and 6.7% (95% CI 2.6–16.1) among pastoral and dairy cattle, respectively. Animals going on transhumance had twice the odds of being seropositive (OR 2.0, 95% CI 1.1–3.8), indicating that animal movements could be implicated in disease expansion. From an ecological perspective, absolute humidity (OR 0.6, 95% CI 0.4–0.9) and shrub density (OR 2.1, 95% CI 1.4–3.2) were associated with seropositivity, which suggests an underlying viral dynamic connecting vertebrate host and ticks in a complex transmission network.ConclusionsThis study demonstrated high seroprevalence levels of CCHFV antibodies in cattle in Cameroon indicating a potential risk to human populations. However, current understanding of the underlying dynamics of CCHFV locally and the real risk for human populations is incomplete. Further studies designed using a One Health approach are required to improve local knowledge of the disease, host interactions and environmental risk factors. This information is crucial to better project the risks for human populations located in CCHFV-suitable ecological niches.     

Protozoa populations are ecosystem engineers that shape prokaryotic community structure and function of the rumen microbial ecosystem

Unicellular eukaryotes are an integral part of many microbial ecosystems where they interact with their surrounding prokaryotic community—either as predators or as mutualists. Within the rumen, one of the most complex host-associated microbial habitats, ciliate protozoa represent the main micro-eukaryotes, accounting for up to 50% of the microbial biomass. Nonetheless, the extent of the ecological effect of protozoa on the microbial community and on the rumen metabolic output remains largely understudied. To assess the role of protozoa on the rumen ecosystem, we established an in-vitro system in which distinct protozoa sub-communities were introduced to the native rumen prokaryotic community. We show that the different protozoa communities exert a strong and differential impact on the composition of the prokaryotic community, as well as its function including methane production. Furthermore, the presence of protozoa increases prokaryotic diversity with a differential effect on specific bacterial populations such as Gammaproteobacteria, Prevotella and Treponema. Our results suggest that protozoa contribute to the maintenance of prokaryotic diversity in the rumen possibly by mitigating the effect of competitive exclusion between bacterial taxa. Our findings put forward the rumen protozoa populations as potentially important ecosystem engineers for future microbiome modulation strategies.Subject terms: Microbial ecology, Food webs     

Functional insight into LOAD-associated microglial response genes

Alzheimer''s disease (AD) is characterized by the presence of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs), neuronal and synaptic loss and inflammation of the central nervous system (CNS). The majority of AD research has been dedicated to the understanding of two major AD hallmarks (i.e. Aβ and NFTs); however, recent genome-wide association studies (GWAS) data indicate neuroinflammation as having a critical role in late-onset AD (LOAD) development, thus unveiling a novel avenue for AD therapeutics. Recent evidence has provided much support to the innate immune system''s involvement with AD progression; however, much remains to be uncovered regarding the role of glial cells, specifically microglia, in AD. Moreover, numerous variants in immune and/or microglia-related genes have been identified in whole-genome sequencing and GWAS analyses, including such genes as TREM2, CD33, APOE, API1, MS4A, ABCA7, BIN1, CLU, CR1, INPP5D, PICALM and PLCG2. In this review, we aim to provide an insight into the function of the major LOAD-associated microglia response genes.     

Tree identity and diversity directly affect soil moisture and temperature but not soil carbon ten years after planting

1. Soil C is the largest C pool in forest ecosystems that contributes to C sequestration and mitigates climate change. Tree diversity enhances forest productivity, so diversifying the tree species composition, notably in managed forests, could increase the quantity of organic matter being transferred to soils and alter other soil properties relevant to the C cycle.
2. A ten‐year‐old tree diversity experiment was used to study the effects of tree identity and diversity (functional and taxonomic) on soils. Surface (0–10 cm) mineral soil was repeatedly measured for soil C concentration, C:N ratio, pH, moisture, and temperature in twenty‐four tree species mixtures and twelve corresponding monocultures (replicated in four blocks).
3. Soil pH, moisture, and temperature responded to tree diversity and identity. Greater productivity in above‐ and below‐ground tree components did not increase soil C concentration. Soil pH increased and soil moisture decreased with functional diversity, more specifically, when species had different growth strategies and shade tolerances. Functional identity affected soil moisture and temperature, such that tree communities with more slow‐growing and shade‐tolerant species had greater soil moisture and temperature. Higher temperature was measured in communities with broadleaf‐deciduous species compared to communities with coniferous‐evergreen species.
4. We conclude that long‐term soil C cycling in forest plantations will likely respond to changes in soil pH, moisture, and temperature that is mediated by tree species composition, since tree species affect these soil properties through their litter quality, water uptake, and physical control of soil microclimates.

     

Differential toxicities of air (mO-LDL) or copper-oxidized LDLs (Cu-LDL) toward endothelial cells.

In vivo low density protein (LDL) oxidation is a progressive phenomenon leading to the presence of minimally and highly oxidized LDLs in the subendothelial arterial space. Oxidized LDLs have been reported to be cytotoxic against endothelial cells. The goal of this study was to determine which of the minimally and highly oxidized LDLs were the most cytotoxic against bovine aortic endothelial cells (BAEC). Both the morphological aspect of the cells themselves, and LDH or MTT tests revealed that mO- or Cu-LDLs had similar cytotoxicity with up to 8 hours of oxidation, showing no relation with the level of LDL oxidation; for longer oxidation times, Cu-LDL cytotoxicity decreased. This phenomenon is linked to their different oxidation kinetics. Moreover, in the initial hours following BAEC incubation with mO- or Cu-LDLs, total cell glutathione dropped, whereas after 16 hours of incubation, highly oxidized Cu-LDL increased the glutathione level in the cell. The biphasic evolution of glutathione concentration corresponds to an autoprotective mechanism of cells against oxidized LDL cytotoxicity. This study suggests that the specific chemical characteristics of the different types of oxidized LDLs should always be precisely described in future assays devoted to studying the biological effects of what are known under the generic term as "oxidized LDLs". This precaution should prevent any confusion in interpreting different studies.     

Truncation of the C terminus of the rat brain Na(+)-Ca(2+) exchanger RBE-1 (NCX1.4) impairs surface expression of the protein.

The C terminus of the rat brain Na(+)-Ca(2+) exchanger (RBE-1; NCX1. 4) (amino acids 875-903) is modeled to contain the last transmembrane alpha helix (amino acids 875-894) and an intracellular extramembraneous tail of 9 amino acids (895-903). Truncation of the last 9 C-terminal amino acids, Glu-895 to stop, did not significantly impair functional expression in HeLa or HEK 293 cells. Truncation, however, of 10 amino acids (Leu-894 to stop; mutant C10) reduced Na(+) gradient-dependent Ca(2+) uptake to 35-39% relative to the wild type parent exchanger, and further truncation of 13 or more amino acids resulted in expression of trace amounts of transport activity. Western analysis indicated that Na(+)-Ca(2+) exchanger protein was produced whether transfection was carried out with functional or non-functional mutants. Immunofluorescence studies of HEK 293 cells expressing N-Flag epitope-tagged wild type and mutant Na(+)-Ca(2+) exchangers revealed that transport activity in whole cells correlated with surface expression. All cells expressing the wild type exchanger or C9 exhibited surface expression of the protein. Only 39% of the cells expressing C10 exhibited surface expression, and none was detected in cells transfected with non-functional mutants C13 and C29. Since functional and non-functional mutants were glycosylated, the C terminus is not mandatory to translocation into the endoplasmic reticulum (ER). Endoglycosidase H digestion of [(35)S]methionine-labeled protein derived from wild type Na(+)-Ca(2+) exchanger and from C10 indicated that resistance to the digestion was acquired after 1 and 5 h of chase, respectively. C29 did not acquire detectable resistance to endoglycosidase H digestion even after 10 h of chase. Taken together, these results suggest that the "cellular quality control machinery" can tolerate the structural change introduced by truncation of the C terminus up to Ser-893 albeit with reduced rate of ER-->Golgi transfer and reduced surface expression of the truncated protein. Further truncation of C-terminal amino acids leads to retention of the truncated protein in the ER, no transfer to the Golgi, and no surface expression.     

Maitotoxin and P2Z/P2X7 purinergic receptor stimulation activate a common cytolytic pore

The effects ofmaitotoxin (MTX) on plasmalemma permeability are similar to thosecaused by stimulation of P2Z/P2X₇ionotropic receptors, suggesting that1) MTX directly activatesP2Z/P2X₇ receptors or2) MTX andP2Z/P2X₇ receptor stimulationactivate a common cytolytic pore. To distinguish between these twopossibilities, the effect of MTX was examined in1) THP-1 monocytic cells before andafter treatment with lipopolysaccharide and interferon-, a maneuverknown to upregulate P2Z/P2X₇receptor, 2) wild-type HEK cells andHEK cells stably expressing theP2Z/P2X₇ receptor, and3) BW5147.3 lymphoma cells, a cellline that expresses functional P2Z/P2X₇ channels that are poorlylinked to pore formation. In control THP-1 monocytes, addition of MTXproduced a biphasic increase in the cytosolic freeCa²⁺ concentration([Ca²⁺]_i);the initial increase reflects MTX-inducedCa²⁺ influx, whereas the secondphase correlates in time with the appearance of large pores and theuptake of ethidium. MTX produced comparable increases in[Ca²⁺]_iand ethidium uptake in THP-1 monocytes overexpressing theP2Z/P2X₇ receptor. In bothwild-type HEK and HEK cells stably expressing theP2Z/P2X₇ receptor, MTX-inducedincreases in[Ca²⁺]_iand ethidium uptake were virtually identical. The response of BW5147.3cells to concentrations of MTX that produced large increases in[Ca²⁺]_ihad no effect on ethidium uptake. In both THP-1 and HEK cells, MTX- andBz-ATP-induced pores activate with similar kinetics and exhibit similarsize exclusion. Last, MTX-induced pore formation, but not channelactivation, is greatly attenuated by reducing the temperature to22°C, a characteristic shared by theP2Z/P2X₇-induced pore. Together,the results demonstrate that, although MTX activates channels that aredistinct from those activated byP2Z/P2X₇ receptor stimulation, thecytolytic/oncotic pores activated by MTX- and Bz-ATP are indistinguishable.

     

Local polynomial regression modeling of human plasma melatonin levels

Accurate characterization of features of the melatonin production curve is important for research in chronobiology. Local polynomial regression is used to model the plasma melatonin concentration curve and obtain consistent and asymptotically normally distributed estimates of synthesis onset and offset times, duration, peak concentration, and area under the curve. A simple production-clearance model for melatonin kinetics provides the connection between plasma concentrations and the melatonin production curve. This model identifies onset and offset times with critical points of derivatives of the concentration curve. The method proposed has the advantage of flexibility and ease of implementation. Local polynomial regression can be shown to produce consistent estimates of the regression curve and parameters of interest. Furthermore, the method can be implemented in any software package with weighted least squares routines.