-
Proceedings of the National Academy of... Aug 2023Polyelectrolyte complexation plays an important role in materials science and biology. The internal structure of the resultant polyelectrolyte complex (PEC) phase...
Polyelectrolyte complexation plays an important role in materials science and biology. The internal structure of the resultant polyelectrolyte complex (PEC) phase dictates properties such as physical state, response to external stimuli, and dynamics. Small-angle scattering experiments with X-rays and neutrons have revealed structural similarities between PECs and semidilute solutions of neutral polymers, where the total scattering function exhibits an Ornstein-Zernike form. In spite of consensus among different theoretical predictions, the existence of positional correlations between polyanion and polycation charges has not been confirmed experimentally. Here, we present small-angle neutron scattering profiles where the polycation scattering length density is matched to that of the solvent to extract positional correlations among anionic monomers. The polyanion scattering functions exhibit a peak at the inverse polymer screening radius of Coulomb interactions, ≈ 0.2 Å. This peak, attributed to Coulomb repulsions between the fragments of polyanions and their attractions to polycations, is even more pronounced in the calculated charge scattering function that quantifies positional correlations of all polymer charges within the PEC. Screening of electrostatic interactions by adding salt leads to the gradual disappearance of this correlation peak, and the scattering functions regain an Ornstein-Zernike form. Experimental scattering results are consistent with those calculated from the random phase approximation, a scaling analysis, and molecular simulations.
PubMed: 37523553
DOI: 10.1073/pnas.2302151120 -
Nature Communications Jul 2023Separating deuterium from hydrogen isotope mixtures is of vital importance to develop nuclear energy industry, as well as other isotope-related advanced technologies. As...
Separating deuterium from hydrogen isotope mixtures is of vital importance to develop nuclear energy industry, as well as other isotope-related advanced technologies. As one of the most promising alternatives to conventional techniques for deuterium purification, kinetic quantum sieving using porous materials has shown a great potential to address this challenging objective. From the knowledge gained in this field; it becomes clear that a quantum sieve encompassing a wide range of practical features in addition to its separation performance is highly demanded to approach the industrial level. Here, the rational design of an ultra-microporous squarate pillared titanium oxide hybrid framework has been achieved, of which we report the comprehensive assessment towards practical deuterium separation. The material not only displays a good performance combining high selectivity and volumetric uptake, reversible adsorption-desorption cycles, and facile regeneration in adsorptive sieving of deuterium, but also features a cost-effective green scalable synthesis using chemical feedstock, and a good stability (thermal, chemical, mechanical and radiolytic) under various working conditions. Our findings provide an overall assessment of the material for hydrogen isotope purification and the results represent a step forward towards next generation practical materials for quantum sieving of important gas isotopes.
Topics: Deuterium; Adsorption; Biological Transport; Hydrogen
PubMed: 37443163
DOI: 10.1038/s41467-023-39871-x -
ACS Catalysis Nov 2023Two bench-stable Fe(II) alkyl complexes [Fe(κPCP-PCP-Pr)(CO)(R)] (R = CHCHCH, CH) were obtained by the treatment of [Fe(κPCP-PCP-Pr)(CO)(H)] with NaNH and subsequent...
Two bench-stable Fe(II) alkyl complexes [Fe(κPCP-PCP-Pr)(CO)(R)] (R = CHCHCH, CH) were obtained by the treatment of [Fe(κPCP-PCP-Pr)(CO)(H)] with NaNH and subsequent addition of CHCHCHBr and CHI, respectively. The reaction proceeds via the anionic Fe(0) intermediate Na[Fe(κPCP-PCP-Pr)(CO)]. The catalytic performance of both alkyl complexes was investigated for the transfer hydrogenation of terminal and internal alkynes utilizing PhSiH and PrOH as a hydrogen source. Precatalyst activation is initiated by migration of the alkyl ligand to the carbonyl C atom of an adjacent CO ligand. In agreement with previous findings, the rate of alkyl migration follows the order Pr > Me. Accordingly, [Fe(κPCP-PCP-Pr)(CO)(CHCHCH)] is the more active catalyst. The reaction takes place at 25 °C with a catalyst loading of 0.5 mol%. There was no overhydrogenation, and in the case of internal alkynes, exclusively, -alkenes are formed. The implemented protocol tolerates a variety of electron-donating and electron-withdrawing functional groups including halides, nitriles, unprotected amines, and heterocycles. Mechanistic investigations including deuterium labeling studies and DFT calculations were undertaken to provide a reasonable reaction mechanism.
PubMed: 37942266
DOI: 10.1021/acscatal.3c04156 -
BioRxiv : the Preprint Server For... Nov 2023Protein tyrosine phosphatase 1B (PTP1B) is a validated therapeutic target for obesity, diabetes, and certain types of cancer. In particular, allosteric inhibitors hold...
Protein tyrosine phosphatase 1B (PTP1B) is a validated therapeutic target for obesity, diabetes, and certain types of cancer. In particular, allosteric inhibitors hold potential for therapeutic use, but an incomplete understanding of conformational dynamics and allostery in this protein has hindered their development. Here, we interrogate solution dynamics and allosteric responses in PTP1B using high-resolution hydrogen-deuterium exchange mass spectrometry (HDX-MS), an emerging and powerful biophysical technique. Using HDX-MS, we obtain a detailed map of the solution dynamics of apo PTP1B, revealing several flexible loops interspersed among more constrained and rigid regions within the protein structure, as well as local regions that exchange faster than expected from their secondary structure and buriedness. We demonstrate that our HDX rate data obtained in solution adds value to predictions of dynamics derived from a pseudo-ensemble constructed from ~200 crystal structures of PTP1B. Furthermore, we report HDX-MS maps for PTP1B with active-site vs. allosteric small-molecule inhibitors. These maps reveal distinct, dramatic, and widespread effects on protein dynamics relative to the apo form, including changes to dynamics in locations distal (>35 Å) from the respective ligand binding sites. These results help shed light on the allosteric nature of PTP1B and the surprisingly far-reaching consequences of inhibitor binding in this important protein. Overall, our work showcases the potential of HDX-MS for elucidating protein conformational dynamics and allosteric effects of small-molecule ligands, and highlights the potential of integrating HDX-MS alongside other complementary methods to guide the development of new therapeutics.
PubMed: 37503000
DOI: 10.1101/2023.07.12.548582 -
Journal of Thrombosis and Haemostasis :... Sep 2023High-molecular weight kininogen (HK) circulates in plasma as a complex with zymogen prekallikrein (PK). HK is both a substrate and a cofactor for activated plasma...
BACKGROUND
High-molecular weight kininogen (HK) circulates in plasma as a complex with zymogen prekallikrein (PK). HK is both a substrate and a cofactor for activated plasma kallikrein, and the principal exosite interactions occur between PK N-terminal apple domains and the C-terminal D6 domain of HK.
OBJECTIVES
To determine the structure of the complex formed between PK apple domains and an HKD6 fragment and compare this with the coagulation factor XI (FXI)-HK complex.
METHODS
We produced recombinant FXI and PK heavy chains (HCs) spanning all 4 apple domains. We cocrystallized PKHC (and subsequently FXIHC) with a 31-amino acid synthetic peptide spanning HK residues Ser565-Lys595 and determined the crystal structure. We also analyzed the full-length FXI-HK complex in solution using hydrogen deuterium exchange mass spectrometry.
RESULTS
The 2.3Å PKHC-HK peptide crystal structure revealed that the HKD6 sequence WIPDIQ (Trp569-Gln574) binds to the apple 1 domain and HK FNPISDFPDT (Phe582-Thr591) binds to the apple 2 domain with a flexible intervening sequence resulting in a bent double conformation. A second 3.2Å FXIHC-HK peptide crystal structure revealed a similar interaction with the apple 2 domain but an alternate, straightened conformation of the HK peptide where residues LSFN (Leu579-Asn583) interacts with a unique pocket formed between the apple 2 and 3 domains. HDX-MS of full length FXI-HK complex in solution confirmed interactions with both apple 2 and apple 3.
CONCLUSIONS
The alternate conformations and exosite binding of the HKD6 peptide likely reflects the diverging relationship of HK to the functions of PK and FXI.
Topics: Humans; Kininogen, High-Molecular-Weight; Factor XI; Prekallikrein; Molecular Weight; Binding Sites; Kininogens; Peptides
PubMed: 37068593
DOI: 10.1016/j.jtha.2023.03.042 -
Nature Communications Dec 2023The conformational ensembles of G protein-coupled receptors (GPCRs) include inactive and active states. Spectroscopy techniques, including NMR, show that agonists,...
The conformational ensembles of G protein-coupled receptors (GPCRs) include inactive and active states. Spectroscopy techniques, including NMR, show that agonists, antagonists and other ligands shift the ensemble toward specific states depending on the pharmacological efficacy of the ligand. How receptors recognize ligands and the kinetic mechanism underlying this population shift is poorly understood. Here, we investigate the kinetic mechanism of neurotensin recognition by neurotensin receptor 1 (NTS) using F-NMR, hydrogen-deuterium exchange mass spectrometry and stopped-flow fluorescence spectroscopy. Our results indicate slow-exchanging conformational heterogeneity on the extracellular surface of ligand-bound NTS. Numerical analysis of the kinetic data of neurotensin binding to NTS shows that ligand recognition follows an induced-fit mechanism, in which conformational changes occur after neurotensin binding. This approach is applicable to other GPCRs to provide insight into the kinetic regulation of ligand recognition by GPCRs.
Topics: Neurotensin; Receptors, Neurotensin; Ligands; Receptors, G-Protein-Coupled; Protein Binding
PubMed: 38071229
DOI: 10.1038/s41467-023-44010-7 -
The Journal of Biological Chemistry Oct 2023Most serine proteases are synthesized as inactive zymogens that are activated by cleavage by another protease in a tightly regulated mechanism. The urokinase-type...
Most serine proteases are synthesized as inactive zymogens that are activated by cleavage by another protease in a tightly regulated mechanism. The urokinase-type plasminogen activator (uPA) and plasmin cleave and activate each other, constituting a positive feedback loop. How this mutual activation cycle begins has remained a mystery. We used hydrogen deuterium exchange mass spectrometry to characterize the dynamic differences between the inactive single-chain uPA (scuPA) and its active form two-chain uPA (tcuPA). The results show that the C-terminal β-barrel and the area around the new N terminus have significantly reduced dynamics in tcuPA as compared with scuPA. We also show that the zymogen scuPA is inactive but can, upon storage, become active in the absence of external proteases. In addition to plasmin, the tcuPA can activate scuPA by cleavage at K158, a process called autoactivation. Unexpectedly, tcuPA can cleave at position 158 even when this site is mutated. TcuPA can also cleave scuPA after K135 or K136 in the disordered linker, which generates the soluble protease domain of uPA. Plasmin cleaves scuPA exclusively after K158 and at a faster rate than tcuPA. We propose a mechanism by which the uPA receptor dimerization could promote autoactivation of scuPA on cell surfaces. These results resolve long-standing controversies in the literature surrounding the mechanism of uPA activation.
PubMed: 37607618
DOI: 10.1016/j.jbc.2023.105179 -
ArXiv Oct 2023Information on the metabolism of tissues in healthy and diseased states plays a significant role in the detection and understanding of tumors, neurodegenerative...
OBJECTIVE
Information on the metabolism of tissues in healthy and diseased states plays a significant role in the detection and understanding of tumors, neurodegenerative diseases, diabetes, and other metabolic disorders. Hyperpolarized carbon-13 magnetic resonance imaging (C-HPMRI) and deuterium metabolic imaging (H-DMI) are two emerging X-nuclei used as practical imaging tools to investigate tissue metabolism. However due to their low gyromagnetic ratios (ɣ = 10.7 MHz/T; ɣ = 6.5 MHz/T) and natural abundance, such method required a sophisticated dual-tuned radiofrequency (RF) coil.
METHODS
Here, we report a dual-tuned coaxial transmission line (CTL) RF coil agile for metabolite information operating at 7T with independent tuning capability. The design analysis has demonstrated how both resonant frequencies can be individually controlled by simply varying the constituent of the design parameters.
RESULTS
Numerical results have demonstrated a broadband tuning range capability, covering most of the X-nucleus signal, especially the C and H spectra at 7T. Furthermore, in order to validate the feasibility of the proposed design, both dual-tuned H/C and H/H CTLs RF coils are fabricated using a semi-flexible RG-405 .086" coaxial cable and bench test results (scattering parameters and magnetic field efficiency/distribution) are successfully obtained.
CONCLUSION
The proposed dual-tuned RF coils reveal highly effective magnetic field obtained from both proton and heteronuclear signal which is crucial for accurate and detailed imaging.
SIGNIFICANCE
The successful development of this new dual-tuned RF coil technique would provide a tangible and efficient tool for ultrahigh field metabolic MR imaging.
PubMed: 37502626
DOI: No ID Found -
African Health Sciences Sep 2023This study aims to evaluate the relation of body mass index (BMI) to fat mass among children by two techniques impedancemetry and deuterium oxide dilution (DO).
OBJECTIVES
This study aims to evaluate the relation of body mass index (BMI) to fat mass among children by two techniques impedancemetry and deuterium oxide dilution (DO).
METHODS
This study was carried out in 156 schoolchildren aged between 8 and 11 years. The children received interrogation specifying lifestyle and food habits. Body composition was determined using the impedancemetry and D2O technique.
RESULTS
The results showed a difference between the percentage of obese and overweight children according to BMIZ classification (30.1%), bioelectrical impedance method (14.7%) and DO technique (42.9%). Despite the difference between the last two classifications, we found a significant correlation between body fat percentages determined by impedancemetry and DO technique (r = 0.695, p<0.01). Bioelectrical impedance analysis underestimated %BF by 78.02% in overall children, by 70.05% in boys and by 84.73% in girls compared to DO technique.
CONCLUSION
This study has demonstrated that the percentage of overweight and obesity varied according the methods used. Further development of body composition methods is needed in children for the real determination of the obesity prevalence and therefore a better monitoring of this public health problem.
Topics: Male; Female; Child; Humans; Body Mass Index; Deuterium; Overweight; Adipose Tissue; Body Composition; Obesity
PubMed: 38357184
DOI: 10.4314/ahs.v23i3.77 -
International Journal of Molecular... Aug 2023Over the last few years, there has been increasing interest in the use of amorphous carbon thin films with low secondary electron yield (SEY) to mitigate electron...
Over the last few years, there has been increasing interest in the use of amorphous carbon thin films with low secondary electron yield (SEY) to mitigate electron multipacting in particle accelerators and RF devices. Previous works found that the SEY increases with the amount of incorporated hydrogen and correlates with the Tauc gap. In this work, we analyse films produced by magnetron sputtering with different contents of hydrogen and deuterium incorporated via the target poisoning and sputtering of CD molecules. XPS was implemented to estimate the phase composition of the films. The maximal SEY was found to decrease linearly with the fraction of the graphitic phase in the films. These results are supported by Raman scattering and UPS measurements. The graphitic phase decreases almost linearly for hydrogen and deuterium concentrations between 12% and 46% (at.), but abruptly decreases when the concentration reaches 53%. This vanishing of the graphitic phase is accompanied by a strong increase of SEY and the Tauc gap. These results suggest that the SEY is not dictated directly by the concentration of H/D, but by the fraction of the graphitic phase in the film. The results are supported by an original model used to calculate the SEY of films consisting of a mixture of graphitic and polymeric phases.
Topics: Deuterium; Electrons; Motion Pictures; Graphite; Hydrogen; Soot
PubMed: 37629181
DOI: 10.3390/ijms241612999