Fluorescence Experiments Research Articles

Vibrational relaxation of high levels of H2O by collisions with Ar as studied by infrared chemiluminescence.

Vibrational relaxation of H2O(v2,v13) molecules by collisions with Ar was studied at 298K (v2 denotes the bending vibrational mode and v13 denotes the sum of the symmetric, v1, and asymmetric, v3, vibrational modes). The H2O molecules from 14 different exothermic reactions of H-atom abstraction by OH radicals were observed by infrared emission from a fast flow reactor as a function of Ar pressure and reaction time. Numerical kinetic calculations were used to obtain rate constants for stretch-to-bend energy conversion, (v2,v13) → (v2 + 2,v13 - 1), and pure bend relaxation, (v2,v13) → (v2 - 1,v13). Rate constants for states up to v13 = 4 were based on the average values from all reactions. The rate constant for the (2,0) → (1,0) bending relaxation is in agreement with the published values from laser-induced fluorescent experiments; the rate constants for higher levels increase with v2. Our average rate constant for the (0,1) → (2,0) stretch-to-bend conversion is somewhat smaller but falls within the uncertainty limit of the published value. The average rate constants for the stretch-to-bend process for (01), (02), (03), and (04) stretching states are (4.3 ± 0.8) × 10-14, (7.7 ± 1.1) × 10-14, (14.3 ± 4.2) × 10-14, and (20.6 ± 6.2) × 10-14cm3molecule-1s-1, respectively.

MOF-303 as an Effective Adsorbent to Clean CH4: SO2 Capture and Detection

Catalysts for the oxidation of CH4 commonly suffer from poisoning by sulfur-containing molecules, such as H2S and SO2. This is a huge problem in real energy applications. As a possible solution, a material capable of selectively capturing the poisoning SO2 is necessary. In this work, water-stable MOF-303 shows high performance for SO2 capture at low pressures (6.21 mmol·g–1 at 298 K and 0.1 bar), ideal characteristics for the adsorption of trace amounts of SO2. Furthermore, MOF-303 showed high chemical stability toward dry and humid SO2 and a remarkable cycling performance with facile regeneration. In addition, MOF-303 displayed high selectivity toward SO2 over CH4 and CO2. Finally, fluorescence experiments proved that the SO2 detection properties of this MOF material are highly promising, even in the presence of CH4 and CO2.

A novel AIEE pillar[5]arene-based conjugated oligomer as paraquat fluorescence turn-off sensor

A novel linear conjugated oligomer (Co-P[5]TPE) based on pillar[5]arene derivative as recognition group and tetraphenylethylene (TPE) unit as fluorophore was designed and synthesized. The Co-P[5]TPE showed aggregation-induced emission enhancement (AIEE) effect in the mixture of dimethyl sulfoxide (DMSO) and water, reaching the maximum fluorescence intensity while the fraction of water was 30%. In the DMSO/H2O solution (VDMSO/Vwater = 7/3), the oligomer sensor displayed “turn-off” fluorescence response (1–I/I0 = 98.7%) towards paraquat (PQ) over other competitive guests. The detection limit (LOD) was 1.54 × 10−8 M and the Stern-Volmer constant (KSV) was determined as 2.144 × 104 M−1 calculating via fluorescent titration experiments. Therefore, the Co-P[5]TPE has highly selective, sensitive and anti-interference properties for sensing PQ. Moreover, the recognition mechanism was specifically investigated through transmission electron microscopy (TEM), dynamic light scattering (DLS) and theoretical calculations involving frontier orbitals (HOMO and LUMO), electrostatic potential (ESP), and the noncovalent interaction (NCI). The cooperation of host-guest chemistry and photoinduced electron transfer (PET) can achieve fluorescence quenching of the chemosensor Co-P[5]TPE for PQ. In addition, the sensor can be used for PQ detection in practical sample.

PEG Gels Significantly Improve the Storage Stability of Nucleic Acid Preparations.

Currently, nucleic acid preparations have gained much attention due to their unique working principle and application value. However, as macromolecular drugs, nucleic acid preparations have complex construction and poor stability. The current methods to promote stability face problems such as high cost and inconvenient operatios. In this study, the hydrophilic pharmaceutical excipient PEG was used to gelate nucleic acid preparations to avoid the random movements of liquid particles. The results showed that PEG gelation significantly improved the stability of PEI25K-based and liposome-based nucleic acid preparations, compared with nucleic acid preparations without PEG gelation. After being stored at 4 °C for 3 days, non-PEG gelled nucleic acid preparations almost lost transfection activity, while PEGylated preparations still maintained high transfection efficiency. Fluorescence experiments showed that this effect was caused by inhibiting particle aggregation. The method described in this study was simple and effective, and the materials used had good biocompatibility. It is believed that this study will contribute to the better development of gene therapy drugs.

Photocatalytic removal of alizarin red and photoinhibition of microbes in the presence of surfactant and Bio-template mediated Ag/SnO2/Nb2O5-SiO2 nanocomposite

Pathogenic microbes and alizarin red being considered as toxic and harmful for human as well as aquatic life and its water contamination can lead to different sorts of diseases. Present study focuses on the synthesis of Ag/SnO2/Nb2O5-SiO2 by new green hydrothermal protocol. UV–vis spectroscopy, FTIR, HRTEM, SEM, EDX, B.E.T and XPS techniques helped in the determination of reaction completion, different optimized conditions, composition, morphology, geometry and average size of the synthesized Ag/SnO2/Nb2O5-SiO2 nanocomposites. The degradation of alizarin red dye was tested in order to investigate the photocatalytic activity of Ag/SnO2/Nb2O5-SiO2 nanocomposite. In a batch reaction system in the presence of fluorescent light photocatalytic experiment was performed. It was verified that at high concentration of dye the photocatalyst degradation ability was affected but increasing the photocatalyst amount helped in the enhancement of dye degradation. Scavenger test verified gave information about the degradation mechanism. The results showed that 99 % dye was degraded in only 20 min. The synthesized nanomaterial was also tested for photoinhibition of Bacillus subtilis (B. subtilis) and Escherichia coli (E. coli). The result shows that the synthesized material has high efficiency against B. subtilis (17 (±0.03) mm) and E. coli (15 (±0.05)). The production of ROS was also examined in the presence of light and nanomaterial. It was also come to know that by combination of these metals and metal oxides helped in the improvement of photocatalytic activity.

Modulating the G-Quadruplex and Duplex DNA Binding by Controlling the Charge of Fluorescent Molecules.

Two fluorescent and non-toxic spirobifluorene molecules bearing either positive (Spiro-NMe3) or negative (Spiro-SO3) charged moieties attached to the same aromatic structure have been investigated as binders for DNA. The novel Spiro-NMe3 containing four alkylammonium substituents interacts with G-quadruplex (G4) DNA structures and shows preference for G4s over duplex by means of FRET melting and fluorescence experiments. The interaction is governed by the charged substituents of the ligands as deduced from the lower binding of the sulfonate analogue (Spiro-SO3). On the contrary, Spiro-SO3 exhibits higher binding affinity to duplex DNA structure than to G4. Both molecules show a moderate quenching of the fluorescence upon DNA binding. The confocal microscopy evaluation shows the internalization of both molecules in HeLa cells and their lysosomal accumulation.

Mechanism of Action of Isopropoxy Benzene Guanidine against Multidrug-Resistant Pathogens.

The increasing emergence of antibiotic resistance is an urgent threat to global health care; thus, there is a need for new therapeutics. Guanidine is the preferred functional group for antimicrobial design and development. Herein, the potential antibacterial activity of the guanidine derivative isopropoxy benzene guanidine (IBG) against multidrug-resistant (MDR) bacteria was discovered. The synergistic antibacterial activity of IBG and colistin was determined by checkerboard assay, time-killing curve, and mouse experiments. The antibacterial mechanism of IBG was verified in fluorescent probe experiments, intracellular oxidative phosphorylation assays, and transcriptome analysis. The results showed that IBG displays efficient antibacterial activity against Gram-positive pathogens and Gram-negative pathogens with permeabilized outer membranes. Further mechanistic studies showed that IBG triggers cytoplasmic membrane damage by binding to phosphatidylglycerol and cardiolipin, leading to the dissipation of proton motive force and accumulation of intracellular ATP. IBG combined with low levels of colistin enhances bacterial outer membrane permeability and increases the accumulation of reactive oxygen species, as further evidenced by transcriptome analysis. Furthermore, the efficacy of IBG with colistin against MDR Escherichia coli in three infection models was demonstrated. Together, these results suggest that IBG is a promising adjuvant of colistin, providing an alternative approach to address the prevalent infections caused by MDR Gram-negative pathogens. IMPORTANCE As antibiotic discovery stagnates, the world is facing a growing menace from the emergence of bacteria that are resistant to almost all available antibiotics. The key to winning this race is to explore distinctive mechanisms of antibiotics. Thus, novel efficient antibacterial agents and alternative strategies are urgently required to fill the void in antibiotic development. Compared with the large amount of money and time required to develop new agents, the antibiotic adjuvant strategy is a promising approach to inhibit bacterial resistance and increase killing of bacteria. In this study, we found that the guanidine derivatives IBG not only displayed efficient antibacterial activities against Gram-positive bacteria but also restored colistin susceptibility of Gram-negative pathogens as an antibiotic adjuvant. More in-depth study showed that IBG is a potential lead to overcome antibiotic resistance, providing new insight into future antibiotic discovery and development.

Designing three digital logic circuits based on two-component molecular systems of a combination of BSA and N, N′-bis(salicylidene) - ethylenediamine

A compound generally has only a single maximum emission wavelength. Therefore, it is relatively difficult to construct a dual-output molecular logic circuit. Herein, a novel fluorescent probe is designed by combining BSA and N, N′-bis(salicylidene)-ethylenediamine. The fluorescence intensity of the probe significantly fluorescence responses at 350 nm or 440 nm changed when stimulated with Zn2+, Fe2+, Cu2+, and EDTAH2Na2. Consequently, three different functional dual-output digit logic circuits are successfully designed in an aqueous solution. This combination is versatile with an additional advantage of water-solubility. Simultaneously, this combination provides a good reference model in exploring Dexter energy transfer in fluorescent experiments.

P-Y/G@NHs sensitizes non-small cell lung cancer cells to radiotherapy via blockage of the PI3K/AKT signaling pathway

Radioresistance represents a common phenomenon found in cancer treatment. Herein, the current study sought to evaluate the effects of a nanodrug delivery system of YSAYPDSVPMMS (YSA) peptide-modified gold nanoparticles-dextran-based hydrogel loaded with paclitaxel-succinic anhydride (P-Y/G@NHs) on non-small cell lung cancer (NSCLC) cell radiosensitivity. Firstly, utilizing the coupling reaction and layer-by-layer assembly technique, P-Y/G@NHs was prepared. The therapeutic effects of the P-Y/G@NHs in NSCLC cells in relation to the PI3K/AKT signaling pathway were examined by assessing the colony formation, apoptosis, and reactive oxygen species (ROS) generation of A549 cells under 10 Gy X-rays irradiation. Moreover, A549 tumor-bearing mice were generated to further validate the therapeutic effect in vivo. We confirmed the successful conjugation of the nanocomposite. Under 10 Gy X-rays irradiation, P-Y/G@NHs reduced the number of colonies of A549 cells, while inducing both cell apoptosis and ROS production. Moreover, P-Y/G@NHs enhanced the radiosensitivity of A549 cells by inhibiting the PI3K/AKT signaling pathway. In vivo fluorescence experiments validated that P-Y/G@NHs effectively-targeted and accumulated at the tumor site in nude mice, thus augmenting the radiosensitivity of tumors without significant immune toxicity or side effects. Conclusively, our findings highlighted that P-Y/G@NHs significantly enhanced the radiosensitivity of NSCLC cells by repressing the PI3K/AKT signaling pathway.

Biochemical and Biophysical Characterization of the Caveolin-2 Interaction with Membranes and Analysis of the Protein Structural Alteration by the Presence of Cholesterol

Caveolin-2 is a protein suitable for the study of interactions of caveolins with other proteins and lipids present in caveolar lipid rafts. Caveolin-2 has a lower tendency to associate with high molecular weight oligomers than caveolin-1, facilitating the study of its structural modulation upon association with other proteins or lipids. In this paper, we have successfully expressed and purified recombinant human caveolin-2 using E. coli. The structural changes of caveolin-2 upon interaction with a lipid bilayer of liposomes were characterized using bioinformatic prediction models, circular dichroism, differential scanning calorimetry, and fluorescence techniques. Our data support that caveolin-2 binds and alters cholesterol-rich domains in the membranes through a CARC domain, a type of cholesterol-interacting domain in its sequence. The far UV-CD spectra support that the purified protein keeps its folding properties but undergoes a change in its secondary structure in the presence of lipids that correlates with the acquisition of a more stable conformation, as shown by differential scanning calorimetry experiments. Fluorescence experiments using egg yolk lecithin large unilamellar vesicles loaded with 1,6-diphenylhexatriene confirmed that caveolin-2 adsorbs to the membrane but only penetrates the core of the phospholipid bilayer if vesicles are supplemented with 30% of cholesterol. Our study sheds light on the caveolin-2 interaction with lipids. In addition, we propose that purified recombinant caveolin-2 can provide a new tool to study protein-lipid interactions within caveolae.

Effects of secondary impinging on flow features and mixing performance in T-T jet reactors

The improvement of mixing performance for the micro/mini impinging jet reactor is a pivotal and attractive topic in the chemical industry. In the present study, the Planar Laser-Induced Fluorescence (PLIF) experiment and numerical simulation on a novel T-T jet reactor that generated secondary impinging were carried out. In the T-T jet reactor, the influence of secondary impinging on various flow regimes at diverse Reynolds numbers was investigated in detail. The results show that, compared with the classical T jet reactor, the mixing of different flow regimes is intensified by the secondary impinging. The number and shape of the impingement planes of the segregated flow and vortex flow are changed. The steady engulfment flow generates more fluid filaments under the secondary impinging. The agglomerate created by the vortex-merging of unsteady engulfment flow is strengthened and the flow topology of the unsteady symmetric flow is modified. All the above indicates that the mixing performance is improved. In addition, the impact of the T-T gap ratio (κ = l/w, where l and w are the width of the T-T gap and the inlet channel, respectively) on flow characteristics and mixing performance in the T-T jet reactor was also considered. The configuration with the lower T-T gap ratio, i.e., κ = 0.2, presented a better global mixing performance than those with the larger T-T gap ratios, i.e., κ = 0.6 and 1.0.

Molecular mechanism of ion channel protein TMEM16A regulated by natural product of narirutin for lung cancer adjuvant treatment

Cancer chemotherapy drugs are widely criticized for their serious side effects and low cure rate. Therefore, adjuvant therapy as a combination with chemotherapy administration is being accepted by many patients. However, unclear drug targets and mechanisms limit the application of adjuvant treatment. In this study, we confirmed TMEM16A is a key drug target for lung adenocarcinoma, and narirutin is an effective anti-lung adenocarcinoma natural product. Virtual screening and fluorescence experiments confirmed that narirutin inhibits the molecular target TMEM16A, which is specific high-expression in lung adenocarcinoma. Molecular dynamics simulations and electrophysiological experiments revealed the precise molecular mechanism of narirutin regulating TMEM16A. The anticancer effect of narirutin and its synergistic effect on cisplatin were explored by cell proliferation, migration, and apoptosis assays. The signaling pathways regulated by narirutin were analyzed by western blot. Tumor xenograft mice experiments demonstrated the synergistic anticancer effect of narirutin and cisplatin, and the side effects of high concentrations of cisplatin were almost eliminated. Pharmacokinetic experiments showed the biological safety of narirutin is satisfactory in vivo. Based on the significant anticancer effect and high biosafety, naringin has great potential as a functional food in the adjuvant treatment of lung cancer.

Antibiofilm effect and mechanism of protocatechuic aldehyde against Vibrio parahaemolyticus.

This study investigated the effect of protocatechuic aldehyde (PCA) on Vibrio parahaemolyticus biofilm formation and its effects on gene expression. Crystal violet assay, metabolic activity assay, and fluorescence experiments were used to evaluate the antibiofilm activities of PCA and to reveal its possible antibiofilm mechanisms using transcriptomic analysis. The results indicated that the minimum antibacterial concentration of PCA against V. parahaemolyticus was 300 μg/mL. PCA (9.375 μg/mL) inhibited biofilm generation and adhesion of the mature biofilm. PCA (75 μg/mL) significantly reduced the metabolic viability of V. parahaemolyticus, reduced polysaccharide production, and inhibited cell surface flagella-mediated swimming and aggregation phenotypes. Meanwhile, transcriptome analysis showed that the key genes of V. parahaemolyticus expressed under PCA (75 μg/mL) inhibition were mainly related to biofilm formation (pfkA, galE, narL, and oppA), polysaccharide production and adhesion (IF, fbpA, and yxeM), and motility (cheY, flrC, and fliA). By regulating these key genes, PCA reduced biofilm formation, suppressed polysaccharide production and transport, and prevented the adhesion of V. parahaemolyticus, thereby reducing the virulence of V. parahaemolyticus. This study demonstrated that protocatechuic aldehyde can be used to control V. parahaemolyticus biofilm to ensure food safety.

Abstract 13377: Modulating Mitochondrial Phosphate Transport Shapes Intracellular Ca Signaling to Impact Arrhythmogenesis

Introduction: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a stress-induced arrhythmic syndrome due to genetic defects of the sarcoplasmic reticulum (SR) Ca release channel complex of ryanodine receptor 2 (RyR2). Our recent study suggests that mitochondria function as a Ca buffer to absorb RyR2-mediated aberrant Ca release and thus mitigate its detrimental consequences in CPVT. Mitochondrial phosphate (Pi) transport has been shown to play a role in both mitochondrial Ca uptake and buffering. Hypothesis: We hypothesize that modulating mitochondrial Pi transport impacts arrhythmogenesis in CPVT by altering mitochondrial Ca uptake and buffering. Methods: Ventricular myocytes were isolated from a genetic CPVT model of CASQ2 knockout (Cnull) mouse. Fluorescent imaging experiments were performed with live cells to examine intracellular Ca dynamics and cellular arrhythmic burden. Mitochondrial Pi transport was modulated by a pharmacological inhibitor or manipulating cytosolic Pi concentration. Results: In the presence of β agonist isoproterenol, an inhibitor of mitochondrial Pi carrier N-ethylmaleimide (NEM) significantly exacerbated Ca handling of intact Cnull cells, resulting in more than 60% of cells displaying pacing-independent Ca oscillations. The NEM treatment also significantly increased the amplitude of cytosolic Ca transient and SR Ca content. Consistent with results obtained in intact cells, NEM treatment exacerbated arrhythmogenic Ca waves and reduced mitochondrial Ca uptake in permeabilized Cnull cells. Moreover, inhibiting mitochondrial Pi transport by lowering cytosolic Pi concentration also increased the frequency of Ca waves and reduced mitochondria Ca uptake in permeabilized Cnull cells. On the contrary, increasing cytosolic Pi concentration reduced the frequency of Ca waves and increased mitochondrial Ca uptake in permeabilized Cnull cells. Conclusions: Modulating mitochondrial Pi transport impacts arrhythmogenesis in CPVT cells through altering mitochondrial Ca uptake and buffering. Enhancing mitochondrial Pi transport may represent a promising therapeutic strategy to reduce arrhythmogenic Ca waves and cardiac arrhythmias in CPVT.

In-silico and in-detail experimental interaction studies of new antitumor Zn(II) complex with CT-DNA and serum albumin

In this study, a novel Zn(II) complex with the formula [Zn(pyrr-ac)2] (pyrr-ac: pyrrolidineacetate) was synthesized and characterized through molar conductivity, elemental analysis, 1H Nuclear Magnetic Resonance (1H NMR), UV-Visible spectroscopy, and Fourier transform infrared (FT-IR) methods. B3LYP level of DFT method along with aug-cc-pVTZ-PP/6-311G(d,p) basis set was utilized to perform the geometry optimization and HOMO-LUMO analysis. In addition, MEP, NLO and NBO computations were also performed at the same level of theory. In vitro antitumor activity of the mentioned complex on leukemia cell line, K562, was investigated using the MTT assay which surprisingly revealed the effective antitumor activity of the studied zinc complex. Interaction of this compound with biological macromolecules viz., CT-DNA and BSA was studied via different spectroscopic methods. The results of fluorescence experiment displayed that the metal complex binds to both macromolecules through hydrogen bond (H-bond) and van der Waals (vdW) forces. UV-Vis tests indicated a decline in the absorption spectra of CT-DNA/BSA in the presence of the compound. The interaction was further corroborated for CT-DNA via gel electrophoresis, CD spectroscopy and viscosity experiments and for BSA using CD spectroscopy. Furthermore, molecular docking simulation was done to evaluate the nature of interaction between the aforementioned zinc complex and CT-DNA/BSA. These results were in agreement with experimental findings and demonstrated that the main interaction is hydrogen bonding. The above type of investigations may provide a pathway through which zinc complexes join the anticancer category. The in-silico and in-vitro results confirm that the newly made [Zn(pyrr-ac)2] complex interacts with CT-DNA than BSA. Communicated by Ramaswamy H. Sarma

The cooperative folding of annexin A2 relies on a transient nonnative intermediate

Annexins (Anxs) are a family of highly homologous proteins that bind and aggregate lipid vesicles in the presence of calcium. All members of the family contain a variable N-terminus determining specific functions, followed by a conserved core region responsible for the general calcium-dependent lipid-binding property. The core structure consists of four homologous domains (DI–DIV), each consisting of a right-handed super-helix of five α-helices. We present data from a combination of site-directed mutagenesis, NMR, and circular dichroism showing that the G25–D34 region of the N-terminus as well as the contacts between residues D38A, R63A, and Q67A of AnxA2-DI are crucial for the autonomous folding and stability of DI of AnxA2. However, we also show that the folding of the full-length protein is very robust in that mutations and truncations that disrupted the folding of AnxA2-DI did not abolish the folding of full-length AnxA2, only lowering its thermal stability. This robustness of the folding of full-length AnxA2 is likely to be mediated by the existence of at least one transient nonnative intermediate as suggested by our kinetic data using stopped-flow fluorescence experiments. We also show that hydrophobic amino acids in AnxA2-DI involved in interfacial contacts with AnxA2-DIV are important for the cooperative folding and stability of the full-length protein. Mutating all of the V57E-V98R-G101Y residues in AnxA2-DI did not affect the folding of the domain, only its stability, but prevented the cooperative folding of the full-length protein. Our collective results favor a highly cooperative and robust folding process mediated by alternative intermediate steps. Since AnxA2 is a multifunctional protein involved in several steps of the progression of cell transformation, these data on structure and folding pathways are therefore crucial to designing anticancer drugs targeting AnxA2.

Advances in antitumor research of CA-4 analogs carrying quinoline scaffold

Combretastatin A-4 (CA-4) is a potent inhibitor of tubulin polymerization and a colchicine binding site inhibitor (CBSI). The structure-activity relationship study of CA-4 showed that the cis double bond configuration and the 3,4,5-trimethoxy group on the A ring were important factors to maintain the activity of CA-4. Therefore, starting from this condition, chemists modified the double bond and also substituted 3,4,5-trimethoxyphenyl with various heterocycles, resulting in a new generation of CA-4 analogs such as chalcone, Flavonoid derivatives, indole, imidazole, etc. Quinoline derivatives have strong biological activity and have been sought after by major researchers for their antitumor activity in recent years. This article reviews the research progress of novel CA-4 containing quinoline analogs in anti-tumor from 1992 to 2022 and expounds on the pharmacological mechanisms of these effective compounds, including but not limited to apoptosis, cell cycle, tubulin polymerization inhibition, immune Fluorescence experiments, etc., which lay the foundation for the subsequent development of CA-4 containing quinoline analogs for clinical use.

Low-lying dipole strength distribution inPb204

Dipole and quadrupole strength distribution of $^{204}\mathrm{Pb}$ was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced using an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 136 states resonantly excited at energies from 3.6 to 8.4 MeV. Spins of the excited states were deduced by angular distribution ratios of $\ensuremath{\gamma}$ rays observed at scattering angles of ${90}^{\ensuremath{\circ}}$ and ${127}^{\ensuremath{\circ}}$ with respect to the incident $\ensuremath{\gamma}$ beam. The analysis of the measured $\ensuremath{\gamma}$-ray spectra includes the quasicontinuum of levels at high energy. Monte Carlo simulation of $\ensuremath{\gamma}$-ray cascades were performed to obtain the intensities of inelastic transitions and branching ratios of the ground-state transitions. The present experimental results were used to investigate the electric dipole $(E1)$ strengths by comparison with predictions from the quasiparticle-phonon model with the self-consistent energy density functional.

Model-independent determination of the dipole response of Zn66 using quasimonoenergetic and linearly polarized photon beams

[Background] Photon strength functions are an important ingredient in calculations relevant for the nucleosynthesis of heavy elements. The relation to the photoabsorption cross section allows to experimentally constrain photon strength functions by investigating the photo-response of atomic nuclei. [Purpose] We determine the photoresponse of $^{66}$Zn in the energy region of 5.6 MeV to 9.9 MeV and analyze the contribution of the "elastic" decay channel back to the ground state. In addition, for the elastic channel electric and magnetic dipole transitions were separated. [Methods] Nuclear resonance fluorescence experiments were performed using a linearly-polarized quasi-monoenergetic photon beam at the High Intensity $\gamma$-ray Source. Photon beam energies from 5.6 to 9.9 MeV with an energy spread of about 3% were selected in steps of 200-300 keV. Two High Purity Germanium detectors were used for the subsequent $\gamma$-ray spectroscopy. [Results] Full photoabsorption cross sections are extracted from the data making use of the monoenergetic character of the photon beam. For the ground-state decay channel, the average contribution of electric and magnetic dipole strengths is disentangled. The average branching ratio back to the ground state is determined as well. [Conclusions] The new results indicate lower cross sections when compared to the values extracted from a former experiment using bremsstrahlung on $^{66}$Zn. In the latter, the average branching ratio to the ground state is estimated from statistical-model calculations in order to analyze the data. Corresponding estimates from statistical-model calculations underestimate this branching ratio compared to the values extracted from the present analysis, which would partly explain the high cross sections determined from the bremsstrahlung data.

Structural studies of human fission protein FIS1 reveal a dynamic region important for GTPase DRP1 recruitment and mitochondrial fission

Fission protein 1 (FIS1) and dynamin-related protein 1 (DRP1) were initially described as being evolutionarily conserved for mitochondrial fission, yet in humans the role of FIS1 in this process is unclear and disputed by many. In budding yeast where Fis1p helps to recruit the DRP1 ortholog from the cytoplasm to mitochondria for fission, an N-terminal "arm" of Fis1p is required for function. The yeast Fis1p arm interacts intramolecularly with a conserved tetratricopeptide repeat core and governs invitro interactions with yeast DRP1. In human FIS1, NMR and X-ray structures show different arm conformations, but its importance for human DRP1 recruitment is unknown. Here, we use molecular dynamics simulations and comparisons to experimental NMR chemical shifts to show the human FIS1 arm can adopt an intramolecular conformation akin to that observed with yeast Fis1p. This finding is further supported through intrinsic tryptophan fluorescence and NMR experiments on human FIS1 with and without the arm. Using NMR, we observed the human FIS1 arm is also sensitive to environmental changes. We reveal the importance of these findings in cellular studies where removal of the FIS1 arm reduces DRP1 recruitment and mitochondrial fission similar to the yeast system. Moreover, we determined that expression of mitophagy adapter TBC1D15 can partially rescue arm-less FIS1 in a manner reminiscent of expression of the adapter Mdv1p in yeast. These findings point to conserved features of FIS1 important for its activity in mitochondrial morphology. More generally, other tetratricopeptide repeat-containing proteins are flanked by disordered arms/tails, suggesting possible common regulatory mechanisms.