Structural and functional analysis of the GABARAP interaction motif (GIM)

Through the canonical LC3 interaction motif (LIR), [W/F/Y]‐X₁‐X₂‐[I/L/V], protein complexes are recruited to autophagosomes to perform their functions as either autophagy adaptors or receptors. How these adaptors/receptors selectively interact with either LC3 or GABARAP families remains unclear. Herein, we determine the range of selectivity of 30 known core LIR motifs towards individual LC3s and GABARAPs. From these, we define a I nteraction 相似文献   

Using Field-Based Species Sensitivity Distributions to Infer Multiple Causes

We describe a new way to develop evidence of causes of biological effects using field-based species sensitivity distributions (SSDs) and show how evidence can be compared when genera or effect endpoints are different among potentially causal agents. To evaluate if a cause is sufficient to elicit an effect, we developed a general SSD. A cause was judged sufficient if the intensity of the stressor at the site predicted the observed proportion of extirpation. To evaluate if an effect is specific to a cause, we developed site-specific SSDs using field-based effect levels of genera occurring in the locality of the study. An effect was judged specific to a cause if susceptible genera were absent and tolerant genera were present. Field-based SSDs were used to assess nutrients and conductivity. Other associations were used to assess metals, sediment, dissolved oxygen, and temperature. A case study at Pigeon Roost Creek, Tennessee, USA, illustrates how the SSDs are used to infer multiple causes. A weight-of-evidence analysis identified nutrients and sediment as probable causes but another unidentified agent appears to be acting as well. This inferential approach has broad application and the causal models for conductivity, nutrients, and deposited sediment can be used at other locations.     

Calcium dependence of proteinase-activated receptor 2 and cholecystokinin-mediated amylase secretion from pancreatic acini

Pancreatic acini secrete digestive enzymes in response to a variety of secretagogues including CCK and agonists acting via proteinase-activated receptor-2 (PAR2). We employed the CCK analog caerulein and the PAR2-activating peptide SLIGRL-NH(2) to compare and contrast Ca(2+) changes and amylase secretion triggered by CCK receptor and PAR2 stimulation. We found that secretion stimulated by both agonists is dependent on a rise in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and that this rise in [Ca(2+)](i) reflects both the release of Ca(2+) from intracellular stores and accelerated Ca(2+) influx. Both agonists, at low concentrations, elicit oscillatory [Ca(2+)](i) changes, and both trigger a peak plateau [Ca(2+)](i) change at high concentrations. Although the two agonists elicit similar rates of amylase secretion, the rise in [Ca(2+)](i) elicited by caerulein is greater than that elicited by SLIGRL-NH(2). In Ca(2+)-free medium, the rise in [Ca(2+)](i) elicited by SLIGRL-NH(2) is prevented by the prior addition of a supramaximally stimulating concentration of caerulein, but the reverse is not true; the rise elicited by caerulein is neither prevented nor reduced by prior addition of SLIGRL-NH(2). Both the oscillatory and the peak plateau [Ca(2+)](i) changes that follow PAR2 stimulation are prevented by the phospholipase C (PLC) inhibitor U73122, but U73122 prevents only the oscillatory [Ca(2+)](i) changes triggered by caerulein. We conclude that 1) both PAR2 and CCK stimulation trigger amylase secretion that is dependent on a rise in [Ca(2+)](i) and that [Ca(2+)](i) rise reflects release of calcium from intracellular stores as well as accelerated influx of extracellular calcium; 2) PLC mediates both the oscillatory and the peak plateau rise in [Ca(2+)](i) elicited by PAR2 but only the oscillatory rise in [Ca(2+)](i) elicited by CCK stimulation; and 3) the rate of amylase secretion elicited by agonists acting via different types of receptors may not correlate with the magnitude of the [Ca(2+)](i) rise triggered by those different types of secretagogue.     

Influence of cold acclimation on membrane injury in frozen plant tissue

Cold-acclimated twigs of Amelanchier alnifolia Nutt. released less HCN at −4.5 C than nonacclimated twigs following slow freezing to −25 C or rapid freezing to −78 C. Cold-acclimated twigs frozen slowly to −25 C released more HCN than cold-acclimated twigs frozen only to −4.5 C. Cold-acclimated twigs frozen slowly to −25 C and then rapidly to −78 C released less HCN at −4.5 C than cold-acclimated twigs frozen rapidly to −78 C. In general, K⁺ efflux and the inability to reduce triphenyl tetrazolium chloride following freezing and thawing paralleled HCN release at −4.5 C. Because low K⁺ efflux and high triphenyl tetrazolium chloride reduction are known to depend upon membrane integrity, the increased K⁺ efflux and the decreased triphenyl tetrazolium chloride reduction following freezing and thawing provide indirect evidence that HCN release at −4.5 C is a measure of membrane damage in frozen cells.     

Induction of the Galpha(q) signaling cascade by the human immunodeficiency virus envelope is required for virus entry

Binding of human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) with the primary receptor CD4 and one of two coreceptors, CXCR4 or CCR5, activates a signaling cascade resulting in Rac-1 GTPase activation and stimulation of actin cytoskeletal reorganizations critical for HIV-1-mediated membrane fusion. The mechanism by which HIV-1 Env induces Rac-1 activation and subsequent actin cytoskeleton rearrangement is unknown. In this study, we show that Env-mediated Rac-1 activation is dependent on the activation of Galpha(q) and its downstream targets. Fusion and Rac-1 activation are mediated by Galpha(q) and phospholipase C (PLC), as shown by attenuation of fusion and Rac-1 activation in cells either expressing small interfering RNA (siRNA) targeting Galpha(q) or treated with the PLC inhibitor U73122. Rac-1 activation and fusion were also blocked by multiple protein kinase C inhibitors, by inhibitors of intracellular Ca2+ release, by Pyk2-targeted siRNA, and by the Ras inhibitor S-trans,trans-farnesylthiosalicylic acid (FTS). Fusion was blocked without altering cell viability or cell surface localization of CD4 and CCR5. Similar results were obtained when cell fusion was induced by Env expressed on viral and cellular membranes and when cell lines or primary cells were the target. Treatment with inhibitors and siRNA specific for Galpha(i) or Galpha(s) signaling mediators had no effect on Env-mediated Rac-1 activation or cell fusion, indicating that the Galpha(q) pathway alone is responsible. These results could provide a new focus for therapeutic intervention with drugs targeting host signaling mediators rather than viral molecules, a strategy which is less likely to result in resistance.     

Explaining geographical variation in the isotope composition of mouse lemurs (Microcebus)

Aim We sought to quantify geographical variation in the stable isotope values of mouse lemurs (Microcebus) and to determine whether this variation reflects trophic differences among populations or baseline isotopic differences among habitats. If the latter pattern is demonstrated, then Microcebus can become a proxy for tracking baseline habitat isotopic variability. Establishing such a baseline is crucial for identifying niche partitioning in modern and ancient communities. Location We studied five species of Microcebus from eight distinct habitats across Madagascar. Methods We compared isotopic variation in C₃ plants and Microcebus fur within and among localities. We predicted that carbon and nitrogen isotope values of Microcebus should: (1) vary as a function of abiotic variables such as rainfall and temperature, and (2) covary with isotopic values in plants. We checked for trophic differences among Microcebus populations by comparing the average difference between mouse lemur and plant isotope values for each locality. We then used multiple regression models to explain spatial isotope variation in mouse lemurs, testing a suite of explanatory abiotic variables. Results We found substantial isotopic variation geographically. Ranges for mean isotope values were similar for both Microcebus and plants across localities (carbon 3.5–4.0‰; nitrogen 10.5–11.0‰). Mean mouse lemur and plant isotope values were lowest in cool, moist localities and highest in hot, dry localities. Rainfall explained 58% of the variation in Microcebus carbon isotope values, and mean plant nitrogen isotope values explained 99.7% of the variation in Microcebus nitrogen isotope values. Average differences between mouse lemur and plant isotope values (carbon 5.0‰; nitrogen 5.9‰) were similar across localities. Main conclusions Isotopic data suggest that trophic differences among Microcebus populations were small. Carbon isotope values in mouse lemurs were negatively correlated with rainfall. Nitrogen isotope values in Microcebus and plants covaried. Such findings suggest that nitrogen isotope values for Microcebus are a particularly good proxy for tracking baseline isotopic differences among habitats. Our results will facilitate future comparative research on modern mouse lemur communities, and ecological interpretations of extinct Holocene communities.