Fe-Doped CoS2 Nanoarrays: Efficient Electrocatalytic Nitrate Reduction to Ammonia under Ambient Conditions.

The electrocatalytic nitrate reduction reaction (NO3 - RR) enables the reduction of nitrate to ammonium ions under ambient conditions. It was considered as an alternative reaction for the production of ammonia (NH3 ) in recent years. In this paper, we report that the Fe doping CoS2 nanoarrays can effectively catalyze the formation of NH3 from nitrate (NO3 - ) under ambient conditions. This is mainly due to the increase of the NO3 - reaction active site by Fe doping and the porous nanostructure of the catalyst, which greatly improves the catalytic activity. Specifically, at -0.9 V vs. RHE, the NH3 yield rate (RNH3 ) of Fe-CoS2 /CC is 17.8×10-2  mmol h-1 cm-2 with Faraday Efficiency (FE) of 88.93 %. Besides, such catalyst shows good durability and catalytic stability, which provides the possibility for the future application of electrocatalytic NH3 production.

The role of protected areas in land use/land cover change and the carbon cycle in the conterminous United States.

Protected areas (PAs) cover about 22% of the conterminous United States. Understanding their role on historical land use and land cover change (LULCC) and on the carbon cycle is essential to provide guidance for environmental policies. In this study, we compiled historical LULCC and PAs data to explore these interactions within the terrestrial ecosystem model (TEM). We found that intensive LULCC occurred in the conterminous United States from 1700 to 2005. More than 3 million km2 of forest, grassland and shrublands were converted into agricultural lands, which caused 10,607 Tg C release from land ecosystems to atmosphere. PAs had experienced little LULCC as they were generally established in the 20th century after most of the agricultural expansion had occurred. PAs initially acted as a carbon source due to land use legacies, but their accumulated carbon budget switched to a carbon sink in the 1960s, sequestering an estimated 1,642 Tg C over 1700-2005, or 13.4% of carbon losses in non-PAs. We also find that PAs maintain larger carbon stocks and continue sequestering carbon in recent years (2001-2005), but at a lower rate due to increased heterotrophic respiration as well as lower productivity associated to aging ecosystems. It is essential to continue efforts to maintain resilient, biodiverse ecosystems and avoid large-scale disturbances that would release large amounts of carbon in PAs.

Chlorophyll fluorescence tracks seasonal variations of photosynthesis from leaf to canopy in a temperate forest.

Accurate estimation of terrestrial gross primary productivity (GPP) remains a challenge despite its importance in the global carbon cycle. Chlorophyll fluorescence (ChlF) has been recently adopted to understand photosynthesis and its response to the environment, particularly with remote sensing data. However, it remains unclear how ChlF and photosynthesis are linked at different spatial scales across the growing season. We examined seasonal relationships between ChlF and photosynthesis at the leaf, canopy, and ecosystem scales and explored how leaf-level ChlF was linked with canopy-scale solar-induced chlorophyll fluorescence (SIF) in a temperate deciduous forest at Harvard Forest, Massachusetts, USA. Our results show that ChlF captured the seasonal variations of photosynthesis with significant linear relationships between ChlF and photosynthesis across the growing season over different spatial scales (R2  = 0.73, 0.77, and 0.86 at leaf, canopy, and satellite scales, respectively; P < 0.0001). We developed a model to estimate GPP from the tower-based measurement of SIF and leaf-level ChlF parameters. The estimation of GPP from this model agreed well with flux tower observations of GPP (R2  = 0.68; P < 0.0001), demonstrating the potential of SIF for modeling GPP. At the leaf scale, we found that leaf Fq '/Fm ', the fraction of absorbed photons that are used for photochemistry for a light-adapted measurement from a pulse amplitude modulation fluorometer, was the best leaf fluorescence parameter to correlate with canopy SIF yield (SIF/APAR, R2  = 0.79; P < 0.0001). We also found that canopy SIF and SIF-derived GPP (GPPSIF ) were strongly correlated to leaf-level biochemistry and canopy structure, including chlorophyll content (R2  = 0.65 for canopy GPPSIF and chlorophyll content; P < 0.0001), leaf area index (LAI) (R2  = 0.35 for canopy GPPSIF and LAI; P < 0.0001), and normalized difference vegetation index (NDVI) (R2  = 0.36 for canopy GPPSIF and NDVI; P < 0.0001). Our results suggest that ChlF can be a powerful tool to track photosynthetic rates at leaf, canopy, and ecosystem scales.

Atmospheric drought dominates changes in global water use efficiency.

Water use efficiency (defined as the ratio of gross primary productivity to plant transpiration, WUET) describes the tradeoff between ecosystem carbon uptake and water loss. However, a comprehensive understanding of the impact of soil and atmospheric moisture deficits on WUET across large regions remains incomplete. Solar-induced chlorophyll fluorescence (SIF) serves as an effective signal for measuring both terrestrial vegetation photosynthesis and transpiration, thereby enabling a rapid response to changes in the physiological status of plants under water stress. The objectives of this study were to: 1) mechanistically calculate WUET using top-of-canopy SIF data and meteorological information by using the revised mechanistic light response model and the Penman-Monteith equation; 2) analyze the effects of atmospheric and soil water deficits on SIF-based WUET by using decoupled soil water content (SWC) and vapor pressure deficit (VPD); 3) evaluate estimated SIF-based WUET against data from 28 eddy covariance (EC) flux sites representing eight different vegetation types. Results indicated that the model performed well in ecosystems with dense canopies, explaining 56 % of the daily variability in EC tower-based WUET. For the years 2019-2020, the global average WUET derived from SIF was 3.49 g C/kg H2O. Notably, this value exceeded 4 g C/kg H2O in tropical rainforest regions near the equator and went beyond 5 g C/kg H2O in the high-latitude regions of the Northern Hemisphere. We found that SIF-based WUET was primarily influenced by VPD rather than SWC in over 90 % of the global vegetated area. The model used in this study increased our ability to mechanistically estimate WUET with SIF at the global scale, thereby highlighting the significance of the global response of SIF-based WUET to water stress, and also enhancing our understanding of the water­carbon cycle in terrestrial ecosystems.

Phage therapy combats pan drug-resistant Acinetobacter baumannii infection safely and efficiently.

Phage therapy offers a promising approach to combat the growing threat of antimicrobial resistance. Yet, key questions remain regarding dosage, administration routes, combination therapy, and the causes of therapeutic failure. In this study, we focused on a novel lytic phage, ФAb4B, which specifically targeted the Acinetobacter baumannii strains with KL160 capsular polysaccharide, including the pan-drug resistant A. baumannii YQ4. ФAb4B exhibited the ability to effectively inhibit biofilm formation and eradicate mature biofilms independently of dosage. Additionally, it demonstrated a wide spectrum of antibiotic-phage synergy and did not show any cytotoxic or haemolytic effects. Continuous phage injections, both intraperitoneally and intravenously over 7 d, showed no acute toxicity in vivo. Importantly, phage therapy significantly improved neutrophil counts, outperforming ciprofloxacin. However, excessive phage injections suppressed neutrophil levels. The combinatorial treatment of phage-ciprofloxacin rescued 91% of the mice, a superior outcome compared to phage alone (67%). The efficacy of the combinatorial treatment was independent of phage dosage. Notably, prophylactic administration of the combinatorial regimen provided no protection, but even when combined with a delayed therapeutic regimen, it saved all the mice. Bacterial resistance to the phage was not a contributing factor to treatment failure. Our preclinical study systematically describes the lytic phage's effectiveness in both in vitro and in vivo settings, filling in crucial details about phage treatment against bacteriemia caused by A. baumannii, which will provide a robust foundation for the future of phage therapy.

A contemporary carbon balance for the Northeast region of the United States.

Development of regional policies to reduce net emissions of carbon dioxide (CO2) would benefit from the quantification of the major components of the region's carbon balance--fossil fuel CO2 emissions and net fluxes between land ecosystems and the atmosphere. Through spatially detailed inventories of fossil fuel CO2 emissions and a terrestrial biogeochemistry model, we produce the first estimate of regional carbon balance for the Northeast United States between 2001 and 2005. Our analysis reveals that the region was a net carbon source of 259 Tg C/yr over this period. Carbon sequestration by land ecosystems across the region, mainly forests, compensated for about 6% of the region's fossil fuel emissions. Actions that reduce fossil fuel CO2 emissions are key to improving the region's carbon balance. Careful management of forested lands will be required to protect their role as a net carbon sink and a provider of important ecosystem services such as water purification, erosion control, wildlife habitat and diversity, and scenic landscapes.

GSPHI: A novel deep learning model for predicting phage-host interactions via multiple biological information.

Emerging evidence suggests that due to the misuse of antibiotics, bacteriophage (phage) therapy has been recognized as one of the most promising strategies for treating human diseases infected by antibiotic-resistant bacteria. Identification of phage-host interactions (PHIs) can help to explore the mechanisms of bacterial response to phages and provide new insights into effective therapeutic approaches. Compared to conventional wet-lab experiments, computational models for predicting PHIs can not only save time and cost, but also be more efficient and economical. In this study, we developed a deep learning predictive framework called GSPHI to identify potential phage and target bacterium pairs through DNA and protein sequence information. More specifically, GSPHI first initialized the node representations of phages and target bacterial hosts via a natural language processing algorithm. Then a graph embedding algorithm structural deep network embedding (SDNE) was utilized to extract local and global information from the interaction network, and finally, a deep neural network (DNN) was applied to accurately detect the interactions between phages and their bacterial hosts. In the drug-resistant bacteria dataset ESKAPE, GSPHI achieved a prediction accuracy of 86.65 % and AUC of 0.9208 under the 5-fold cross-validation technique, significantly better than other methods. In addition, case studies in Gram-positive and negative bacterial species demonstrated that GSPHI is competent in detecting potential Phage-host interactions. Taken together, these results indicate that GSPHI can provide reasonable candidate sensitive bacteria to phages for biological experiments. The webserver of the GSPHI predictor is freely available at http://120.77.11.78/GSPHI/.

Naringenin induces the cell apoptosis of acute myeloid leukemia cells by regulating the lncRNA XIST/miR-34a/HDAC1 signaling.

Acute myeloid leukemia (AML) is a life-threatening aggressive malignancy of the bone marrow and has posed a great challenge to the clinic, due to a lack of fully understanding of the molecular mechanism. Histone deacetylase 1 (HDAC1) has been reported to be a therapeutic target for treating AML. Naringenin (Nar) may act as an anti-leukemic agent and suppress the expression of HDACs. However, the potential underlying mechanism of Nar in suppressing the activity of HDAC1 remains unclear. Here, we found that Nar induced the apoptosis, decreased the expression of lncRNA XIST and HDAC1, and increased the expression of microRNA-34a in HL60 cells. Sh-XIST transfection could induce cell apoptosis. On the contrary, the forced expression of XIST might reverse the biological actions of Nar. XIST could sponge miR-34a, which targeted to degrade HDAC1. The forced expression of HDAC1 could effectively reverse the effects of Nar. Thus, Nar can induce cell apoptosis by mediating the expression of lncRNA XIST/miR-34a/HDAC1 signaling in HL60 cells.

Relationship between Photosynthetic CO2 Assimilation and Chlorophyll Fluorescence for Winter Wheat under Water Stress.

Solar-induced chlorophyll fluorescence (SIF) has a high correlation with Gross Primary Production (GPP). However, studies focusing on the impact of drought on the SIF-GPP relationship have had mixed results at various scales, and the mechanisms controlling the dynamics between photosynthesis and fluorescence emission under water stress are not well understood. We developed a leaf-scale measurement system to perform concurrent measurements of active and passive fluorescence, and gas-exchange rates for winter wheat experiencing a one-month progressive drought. Our results confirmed that: (1) shifts in light energy allocation towards decreasing photochemistry (the quantum yields of photochemical quenching in PSII decreased from 0.42 to 0.21 under intermediate light conditions) and increasing fluorescence emissions (the quantum yields of fluorescence increased to 0.062 from 0.024) as drought progressed enhance the degree of nonlinearity of the SIF-GPP relationship, and (2) SIF alone has a limited capacity to track changes in the photosynthetic status of plants under drought conditions. However, by incorporating the water stress factor into a SIF-based mechanistic photosynthesis model, we show that drought-induced variations in a variety of key photosynthetic parameters, including stomatal conductance and photosynthetic CO2 assimilation, can be accurately estimated using measurements of SIF, photosynthetically active radiation, air temperature, and soil moisture as inputs. Our findings provide the experimental and theoretical foundations necessary for employing SIF mechanistically to estimate plant photosynthetic activity during periods of drought stress.

Response of dryland vegetation under extreme wet events with satellite measures of greenness and fluorescence.

Extreme wet events in central Australia triggered large vegetation responses that contributed greatly to large global land carbon sink anomalies. There remain significant uncertainties on the extent to which these events over dryland vegetation can be monitored and assessed with satellite data. In this study, we investigated the vegetation responses of the major Australian semiarid biomes to two extreme wet events utilizing multi-satellite observations of (1) solar-induced chlorophyll fluorescence (SIF), as a proxy for photosynthetic activity and (2) the enhanced vegetation index (EVI), as a measure of canopy chlorophyll or greenness. We related these satellite observations with gross primary productivity (GPP) estimated from eddy covariance tower sites, as a performance benchmark. The C3-dominated Mulga woodland was the most responsive biome to both wet pulses and exhibited the highest sensitivity to soil moisture. The C4-dominated Hummock grassland was more responsive to the 2011 "big wet" event, relative to the later 2016-2017 wet pulse. EVI swiftly responded to the extreme wet events and showed markedly amplified seasonal amplitude, however, there was a time lag as compared with SIF during the post-wet period, presumably due to the relatively slower chlorophyll degradation in contrast with declines in photosynthetic activity. Despite a robust linear SIF-GPP relationship (r2 ranging from 0.59 to 0.85), the spatially coarse SIF derived from the Global Ozone Monitoring Experiment-2 (GOME-2) yielded high retrieval noise over the xeric biomes, hindering its capacity to capture thoroughly the dryland vegetation dynamics in central Australia. Our study highlights that synchronous satellite observations of greenness and fluorescence can potentially offer an improved understanding of dryland vegetation dynamics and can advance our ability to detect ecosystem alterations under future changing climates.

Building social resilience in North Korea can mitigate the impacts of climate change on food security.

Adaptation based on social resilience is proposed as an effective measure to mitigate hunger and avoid food shocks caused by climate change. But these have not been investigated comprehensively in climate-sensitive regions. North Korea (NK) and its neighbours, South Korea and China, represent three economic levels that provide us with examples for examining climatic risk and quantifying the contribution of social resilience to rice production. Here our data-driven estimates show that climatic factors determined rice biomass changes in NK from 2000 to 2017, and climate extremes triggered reductions in production in 2000 and 2007. If no action is taken, NK will face a higher climatic risk (with continuous high-temperature heatwaves and precipitation extremes) by the 2080s under a high-emissions scenario, when rice biomass and production are expected to decrease by 20.2% and 14.4%, respectively, thereby potentially increasing hunger in NK. Social resilience (agricultural inputs and population development for South Korea; resource use for China) mitigated climate shocks in the past 20 years (2000-2019), even transforming adverse effects into benefits. However, this effect was not significant in NK. Moreover, the contribution of social resilience to food production in the undeveloped region (15.2%) was far below the contribution observed in the developed and developing regions (83.0% and 86.1%, respectively). These findings highlight the importance of social resilience to mitigate the adverse effects of climate change on food security and human hunger and provide necessary quantitative information.

Dual targeting of PD-L1 and PD-L2 by PCED1B-AS1 via sponging hsa-miR-194-5p induces immunosuppression in hepatocellular carcinoma.

BACKGROUND: PD-L1 and PD-L2 are PD-1 ligands (PD-Ls). PD-Ls over-expression is associated with poor prognosis in hepatocellular carcinoma (HCC). However, little is known about how PD-Ls expression is regulated. Here, we investigated the involvement of lncRNA-microRNA network in the regulation of PD-Ls in HCC. METHODS: The expression of PD-Ls, PCED1B-AS1 and hsa-miR-194-5p was measured in 45 pairs of HCC samples. The interaction between PCED1B-AS1 and hsa-miR-194-5p was measured by microRNA pull down and in vitro binding assay. The effects of PCED1B-AS1 knockdown and over-expression on hsa-miR-194-5p and PD-Ls expression were investigated in HCC cell lines. Immunosuppression was evaluated in co-culture of HCC cell line and human T cells. Exosomes were isolated from HCC cells and their effects on receipt cells were investigated. Tumor behaviors were evaluated by in vitro and in vivo assays. RESULTS: PD-L1 expression was highly correlated with PD-L2 expression in HCC. PCED1B-AS1 and hsa-miR-194-5p expression was up-regulated in HCC. PCED1B-AS1 was positively correlated with PD-Ls but negatively correlated hsa-miR-194-5p in HCC. These correlations were cross-validated by TCGA-LIHC dataset. PCED1B-AS1 interacted with hsa-mir-194-5p which inhibited PD-Ls expression. PCED1B-AS1 enhanced the expression of PD-Ls via sponging hsa-mir-194-5p. PCED1B-AS1-induced PD-Ls-mediated immunosuppression in co-cultured T cells. HCC cells released PCED1B-AS1 containing exosomes and the exosomal PCED1B-AS1 enhanced PD-Ls expression in receipt HCC cells while inhibited receipt T cells and macrophages. Blood exosomal PCED1B-AS1 was correlated with HCC PD-Ls expression. Finally, PCED1B-AS1 promoted cell proliferation, colony formation and in vivo tumor formation in xenografted nude mice while inhibited apoptosis. CONCLUSIONS: PCED1B-AS1 enhances the expression and function of PD-Ls via sponging hsa-miR-194-5p to induce immunosuppression in HCC.

Primary colon natural killer (NK)/T-cell lymphoma, nasal type, with perforations: a case report and literature review.

Extranodal natural killer (NK)/T-cell lymphoma-nasal type (ENKTL-NT) is a rare, aggressive subtype of non-Hodgkin's lymphoma associated with Epstein-Barr virus (EBV) infection and has a poor prognosis. ENKTL-NT primarily involves the nasal cavity, and the colon as the primary site has rarely been reported. Its lack of a characteristic clinical presentation makes early diagnosis difficult to diagnose early, and misdiagnosis is common without the use of immunohistochemistry of specimens. To further understand this rare solid tumor, we report a case in a 51-year-old male patient admitted to hospital with abdominal pain as the primary symptom. A provisional diagnosis of gastrointestinal perforation was made on the basis of enhanced computed tomography of the abdomen, and emergency surgery was performed. However, 58 days after discharge, he suffered a second colonic perforation, underwent emergency surgery and was diagnosed with primary colonic ENKTL-NT based on the immunohistochemical results of the surgical specimen. He was transferred to the oncology department for chemotherapy after recovery from surgery, with gemcitabine, oxaliplatin, and pegaspargase as the chemotherapy regimen. To date, he has completed 11 courses of chemotherapy, and is now in a significantly improved general condition with no signs of tumor recurrence. We also reviewed and compared the literature related to primary colonic ENKTL-NT.

Quantitative detection of circulating MT-ND1 as a potential biomarker for colorectal cancer.

Liquid biopsy represents a diagnostic and monitoring tool and the circulating cell-free mitochondrial DNA (mtDNA) plays a vital role in tumor diagnosis and dynamic assessment. Colorectal cancer (CRC) is one of the most common fatal cancers worldwide. Mitochondrially encoded NADH dehydrogenase subunit 1 (MT-ND1) encodes the biggest subunit of respiratory complex I of mtDNA, and mutations in the MT-ND1 are common in CRC. We sought to determine if mutations in circulating MT-ND1 could be a potential biomarker for colorectal cancer. In this study, twenty-two CRC patients at Zhujiang Hospital were included. We mainly used droplet digital PCR to determine the mutation status of MT-ND1, combined with clinical data. In the experiment in vivo, cell-free mtDNA generally presented high concordance with tumor tissues. By quantitative PCR, the MT-ND1 content of plasma in CRC patients was significantly higher than that in healthy individuals (58.01 vs. 0.64, p=0.027). The detection of circulating MT-ND1 content and variants (m.3606 A>G, m.3970 C>T, m.4071 C>T, m.4086 C>T) in cfDNA showed a good correlation with predicted tumor response and progression to chemotherapy. In conclusion, the content and variants of circulating MT-ND1 may become a versatile tool for the diagnosis and monitoring of colorectal cancer.

Author Correction: Tidal wetland resilience to sea level rise increases their carbon sequestration capacity in United States.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Tidal wetland resilience to sea level rise increases their carbon sequestration capacity in United States.

Coastal wetlands are large reservoirs of soil carbon (C). However, the annual C accumulation rates contributing to the C storage in these systems have yet to be spatially estimated on a large scale. We synthesized C accumulation rate (CAR) in tidal wetlands of the conterminous United States (US), upscaled the CAR to national scale, and predicted trends based on climate change scenarios. Here, we show that the mean CAR is 161.8 ± 6 g Cm-2 yr-1, and the conterminous US tidal wetlands sequestrate 4.2-5.0 Tg C yr-1. Relative sea level rise (RSLR) largely regulates the CAR. The tidal wetland CAR is projected to increase in this century and continue their C sequestration capacity in all climate change scenarios, suggesting a strong resilience to sea level rise. These results serve as a baseline assessment of C accumulation in tidal wetlands of US, and indicate a significant C sink throughout this century.

Expression Analysis and Functional Characterization of CER1 Family Genes Involved in Very-Long-Chain Alkanes Biosynthesis in Brachypodium distachyon.

Cuticular wax accumulation and composition affects drought resistance in plants. Brachypodium distachyon plants subjected to water deficit and polyethylene glycol treatments resulted in a significant increase in total wax load, in which very-long-chain (VLC) alkanes were more sensitive to these treatments than other wax compounds, implying that VLC alkanes biosynthesis plays a more important role in drought resistance in B. distachyon. ECERIFERUM1 (CER1) has been reported to encode a core enzyme involved in VLC alkanes biosynthesis in Arabidopsis (Arabidopsis thaliana), but few corresponding genes are investigated in B. distachyon. Here, we identified eight CER1 homologous genes in B. distachyon, namely BdCER1-1 to BdCER1-8, and then analyzed their sequences feature, expression patterns, stress induction, and biochemical activities. These genes had similar protein structure to other reported CER1 and CER1-like genes, but displayed closer phylogenetic relationship to the rice OsGL1 genes. They were further found to exhibit various tissue expression patterns after being induced by abiotic stresses. Among them, BdCER1-8 gene showed extremely high expression in leaves. Heterologous introduction of BdCER1-8 into the Arabidopsis cer1 mutant rescued VLC alkanes biosynthesis. These results indicate that BdCER1 genes are likely to be involved in VLC alkanes biosynthesis of B. distachyon. Taken together, BdCER1-8 seems to play an explicit and predominant role in VLC alkanes biosynthesis in leaf. Our work provides important clues for further characterizing function of CER1 homologous genes in B. distachyon and also an option to improve drought resistance of cereal crops.

Protected areas' role in climate-change mitigation.

Globally, 15.5 million km(2) of land are currently identified as protected areas, which provide society with many ecosystem services including climate-change mitigation. Combining a global database of protected areas, a reconstruction of global land-use history, and a global biogeochemistry model, we estimate that protected areas currently sequester 0.5 Pg C annually, which is about one fifth of the carbon sequestered by all land ecosystems annually. Using an integrated earth systems model to generate climate and land-use scenarios for the twenty-first century, we project that rapid climate change, similar to high-end projections in IPCC's Fifth Assessment Report, would cause the annual carbon sequestration rate in protected areas to drop to about 0.3 Pg C by 2100. For the scenario with both rapid climate change and extensive land-use change driven by population and economic pressures, 5.6 million km(2) of protected areas would be converted to other uses, and carbon sequestration in the remaining protected areas would drop to near zero by 2100.

[Effect of jinshui-liujun decoction on chronic bronchitis in rats].

OBJECTIVE: To study of the quality standard about Jinshui Liujun decoction. METHODS: The chronic broncitis model of rat was induced by injecting LPS into rat's trachea. Then, the number of WBC, SV, PS were detected. RESULTS: Both Jinshui Liujun decoction and hesperidin can improve the content of PS and reduce the number of WBC. There were statistical difference between the therapeutic groups and the model group, and the changes of bronchi between the therapeutic group were similar. But the SV of hesperidin group was bigger than Jinshui Liujun decoction group, and the PS of hesperidin group was less than Jinshui Liujun decoction group. CONCLUSION: It was feasible that the content of hesperidin in Jinshui Liujun decoction was as primary quality control index.

The intrinsic helical propensities of the helical fragments in prion protein under neutral and low pH conditions: a replica exchange molecular dynamics study.

Replica exchange molecular dynamics simulations in neutral and acidic aqueous solutions were employed to study the intrinsic helical propensities of three helices in both Syrian hamster (syPrP) and human (huPrP) prion proteins. The helical propensities of syPrP HA and huPrP HA are very high under both pH conditions, which implies that HA is barely involved in the helix-to-ß transition. The SyPrP HB chain has a strong tendency to adopt an extended conformation, which is possibly involved in the mechanism of infectious prion diseases in Syrian hamster. HuPrP HC has more of a preference for the extended conformation than huPrP HA and huPrP HB do, which leads to the conjecture that it is more likely to be the source of ß-rich structure for human prion protein. We also noticed that the presence of salt bridges is not correlated with helical propensity, indicating that salt bridges do not stabilize helices.