Understanding Rubredoxin Redox Sites by Density Functional Theory Studies of Analogues

Determining the redox energetics of redox site analogues of metalloproteins is essential in unraveling the various contributions to electron transfer properties of these proteins. Since studies of the [4Fe–4S] analogues show that the energies are dependent on the ligand dihedral angles, broken symmetry density functional theory (BS-DFT) with the B3LYP functional and double-ζ basis sets calculations of optimized geometries and electron detachment energies of [1Fe] rubredoxin analogues are compared to crystal structures and gas-phase photoelectron spectroscopy data, respectively, for [Fe­(SCH₃)₄]^0/1–/2–, [Fe­(S₂-<i>o</i>-xyl)₂]^0/1–/2–, and Na⁺[Fe­(S₂-<i>o</i>-xyl)₂]^1–/2– in different conformations. In particular, the study of Na⁺[Fe­(S₂-<i>o</i>-xyl)₂]^1–/2– is the only direct comparison of calculated and experimental gas phase detachment energies for the 1–/2– couple found in the rubredoxins. These results show that variations in the inner sphere energetics by up to ∼0.4 eV can be caused by differences in the ligand dihedral angles in either or both redox states. Moreover, these results indicate that the protein stabilizes the conformation that favors reduction. In addition, the free energies and reorganization energies of oxidation and reduction as well as electrostatic potential charges are calculated, which can be used as estimates in continuum electrostatic calculations of electron transfer properties of [1Fe] proteins

Bioinspired Hierarchical Nanofibrous Silver-Nanoparticle/Anatase–Rutile-Titania Composite as an Anode Material for Lithium-Ion Batteries

A new bioinspired hierarchical nanofibrous silver-nanoparticle/anatase–rutile-titania (Ag-NP/A–R-titania) composite was fabricated by employing a natural cellulose substance (e.g., commercial laboratory cellulose filter paper) as the structural scaffold template, which was composed of anatase-phase titania (A-titania) nanotubes with rutile-phase titania (R-titania) nanoneedles grown on the surfaces and further silver nanoparticles (AgNPs) immobilized thereon. As it was employed as an anode material for lithium-ion batteries (LIBs), high reversible capacity, enhanced rate performance, and excellent cycling stability were achieved as compared with those of the corresponding cellulose-substance-derived nanotubular A-titania, R-titania, heterogeneous anatase/rutile titania (A–R-titania) composite, and commercial P25 powder. This benefited from its unique porous cross-linked three-dimensional structure inherited from the initial cellulose substance scaffold, which enhances the sufficient electrode/electrolyte contact, relieves the severe volume change upon cycling, and improves the amount of lithium-ion storage; moreover, the high loading content of the silver component in the composite improves the electrical conductivity of the electrode. The structural integrity of the composite was maintained upon long-term charge/discharge cycling, indicating its significant stability

Data_Sheet_1_International curriculum for undergraduate sonographer education in China during the COVID-19 era: International remote teaching mode vs. domestic on-site teaching mode.docx

BackgroundSichuan University West China Medical School was the first institution in China to develop an undergraduate sonographer education program in 2016. This program was certificated by American Registry for Diagnostic Medical Sonography (ARDMS) and students are qualified for the ARDMS credential verification test. In this 4-year program, the international curriculum of ultrasound physics and hemodynamics was set for students in the third year since 2018. This study is aimed to compare the teaching effect of international remote teaching mode and domestic on-site teaching mode of this international curriculum before and during the COVID-19 pandemic.MethodsAll undergraduate sonographer students after completing ultrasound physics and hemodynamics in the academic years 2018–2019 (30 students; before the COVID-19 pandemic) and 2020–2021 (47 students; during the COVID-19 pandemic) were included in the study. The scores of 77 students were analyzed for their curriculum. Independent samples t-test or Mann–Whitney test was employed to compare students' scores before and during the COVID-19 pandemic. The Chi-square test was used to compare students' feedback about this curriculum through an online self-administered questionnaire. A p ResultsTotal scores were comprised of four parts: in-class tests, homework, mid-term, and final exam scores. The mean in-class test score for domestic on-site teaching mode during the COVID-19 pandemic was significantly higher than that for international remote teaching mode before the COVID-19 pandemic. However, there was no observed a statistically significant difference in homework, mid-term, final exam, and total scores between the two types of teaching modes. For questionnaire feedback, no significant difference was observed between the two groups regarding the satisfaction toward teachers, class atmosphere, teaching mode, curriculum content, exam difficulty, scores, and knowledge students gained. For the overall evaluation of the curriculum, 73.3% (22/30) of students were very satisfied before the COVID-19 pandemic, while 44.7% (21/47) of students felt very satisfied during the COVID-19 pandemic (p = 0.02).ConclusionThe general teaching effect of domestic on-site teaching mode during the COVID-19 pandemic was comparable to that of international remote teaching mode before the COVID-19 pandemic, and domestic on-site teaching mode may provide a better in-class teaching effect.</p

Bio-Inspired Hierarchical Nanofibrous Fe₃O₄–TiO₂–Carbon Composite as a High-Performance Anode Material for Lithium-Ion Batteries

A bioinspired hierarchical nanofibrous Fe₃O₄–TiO₂–carbon composite was fabricated by employing natural cellulose substance (e.g., filter paper) as both the scaffold and the carbon source and showed improved electrochemical performances when it is employed as an anode material for lithium-ion batteries. FeOOH nanoparticles were first grown uniformly onto the surface of the titania thin-layer precoated cellulose nanofibers, and thereafter, the as-prepared FeOOH–TiO₂–cellulose composite was calcined and carbonized in argon atmosphere at 500 °C for 6 h to produce the Fe₃O₄–TiO₂–carbon composite. The resultant composite possesses a hierarchical structure that was faithfully inherited from the initial cellulose substance, which was composed of titania-coated carbon fibers with corncob-like shaped Fe₃O₄ nanoparticles immobilized on the surfaces. The diameter of the composite nanofiber is ca. 100–200 nm, and the diameter of the Fe₃O₄ nanoparticle is about 30 nm, which is coated with an ultrathin carbon layer with a thickness about 3 nm. This composite displayed superior lithium-ion storage performance. It showed a first-cycle discharge capacity of 1340 mAh/g, delivering a stable reversible capacity of ca. 525 mAh/g after 100 charge–discharge cycles at a current density of 100 mA/g, and the efficiency is as high as ca. 95% of the theoretical value. This is much higher than those of the commercial Fe₃O₄ powder (160 mAh/g) and the Fe₃O₄–carbon counter material (310 mAh/g). It was demonstrated that the thin titania precoating layer (thickness ca. 3–5 nm) is necessary for the high content loading of the Fe₃O₄ nanoparticles onto the carbon nanofibers. Owing to the unique three-dimensional porous network structure of the carbon-fiber scaffold, together with the ultrathin outer carbon-coating layer, the composite showed significantly improved cycling stability and rate capability

Growth phenotypes of HeLa cells knockdown of CBP or SIRT1.

<p>HeLa cells were transfected with 100 nM of different siRNA as indicated. At different time points post transfection, the numbers of viable cells were counted with tryphan blue staining. Random siRNA and siRNA specific for p38/GAPDH or NPAT were controls. Results were mean of triplicates.</p

A model for the regulation of histone gene transcription.

<p>At G1/S transition of a cell cycle, the cellular NAD+/NADH ratio is proper for the assembly of the OCA-S complex which facilitates the recruitment of NPAT to the histone H2B promoter. NPAT, phosphorylated by cyclin E/cdk2, in turn facilitates the recruitment of CBP/p300 and SIRT1 to histone promoters in a global fashion. CBP/p300, which is also phosphorylated by cyclin E/cdk2, enhances histone acetylation on histone promoter regions hence activating S-phase histone transcription. In late S phase, the CBP/p300 association with histone promoters is decreased, likely accompanied by increased SIRT1 recruitment, which in conjunction with more oxidative cellular redox (higher NAD+ level) stimulates the HDAC activity of SIRT1 specifically targeting histone gene promoters hence accounting for declination of histone expression in a coordinated fashion. This model adds another layer of regulation of redox-modulated histone expression.</p

The HAT activity of CBP/p300 is important for histone gene transcription.

<p>(A) HAT activity of ectopically expressed p300. Plasmids pCMV-p300HA which encodes HA-tagged p300 or pcDNA3.1-p300HAT- which encodes p300 (HAT-) mutant were transfected into HeLa (left panels) or 293T cells (right panels). Western-blot was employed to determine protein expression and the HAT activity. (B) Histone H2B and H4 transcription was enhanced by p300HA but not p300 (HAT-). n = 4. (C) p300 (HAT-) mutant was unable to rescue the down-regulation of H2B transcription resulted from CBP knockdown. HeLa cells were co-transfected with siRNA and plasmid DNA as indicated. 48 hours after transfection, cells were harvested for RT-real time qPCR. Comparison between column 2 and 3 was analyzed with unpaired <i>t</i> test. n = 4.</p

SIRT1 associates with histone gene promoters and impacts histone acetylation on target promoters.

<p>(A) SIRT1 associates with histone H2B and H4 promoters. (B) The SIRT1 association with histone promoters requires NPAT. (C) Increased levels of acetylated H3 and H4 on the H2B promoter in SIRT1 knock-down cells. (D) Increased levels of acetylated H3 and H4 on the H4 promoter in SIRT1 knock-down cells. In A–D, n = 3.</p

The acetylation levels of histones at histone gene promoters decrease in cells with p300 knockdown.

<p>(A) p300 downregulation by siRNA resulted in cell accumulation in G1 phase. siRNA transfection was as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022088#pone-0022088-g002" target="_blank">Fig. 2A</a>. (B) Acetylated histone H3 and H4 on the H2B promoter increased in HU treated cells. n = 4. HeLa cells were treated with 2.5 mM of HU for 24 hours before being harvested. HU was dissolved in PBS buffer. (C) Histone H2B promoter acetylation decreased in HU-synchronized cells with p300 knockdown. HeLa cells were transfected with sip300 or control siRNA as indicated. 24 hours after transfection, cells were switched to fresh media with 2.5 mM of HU for another 24 hours. n = 3. (D) Histone H2B mRNA level and histone promoter acetylation level were reduced in p300 knockdown cells in early S phase. Cells synchronized as described in (C) were released into S-phase for 30 minutes before being harvested for FACS, RT-qPCR and ChIP. Comparison of H2B mRNA levels between released control and sip300 groups was analyzed with unpaired <i>t</i> test. n = 4.</p

CBP and p300 associate with histone promoters in an NPAT-dependent manner.

<p>ChIP assays were performed with rabbit anti-CBP or anti-p300 antibodies. (A) CBP and p300 association with the H2B promoter. n = 5. (B) CBP and p300 association with the H4 promoter. n = 5. (C) Co-immunoprecipitation of CBP with NPAT. Whole cell extracts of HeLa cells transfected with pCMV-NPAT were used to carry out co-immunoprecipitation with rabbit anti-CBP antibodies. Precipitated proteins were detected with Western-blot using mouse anti-CBP antibodies or mouse anti-NPAT antibodies as indicated. (D) The efficacy of NPAT knockdown. Western-Blot was performed with rabbit anti-NPAT or rabbit anti-Sti1 antibody as indicated. Sti1 was used as a loading control. (E) Reduced association of CBP and p300 with the H2B promoter in NPAT knockdown cells. n = 3. (F) Reduced association of CBP and p300 with the H4 promoter in NPAT knockdown cells, n = 3.</p