Search NASA⌕ Search

SEARCH · Search NASA

Results for “Circular dichroism spectroscopy”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Plant defensin MtDef4–derived antifungal peptide with multiple modes of action and potential as a bio–inspired fungicide

Chemical fungicides have been instrumental in protecting crops from fungal diseases. However, increasing fungal resistance to many of the single-site chemical fungicides calls for the development of new antifungal agents with novel modes of action (MoA). The sequence-divergent cysteine-rich antifungal defensins with multisite MoA are promising starting templates for design of novel peptide-based fungicides. Here, we experimentally tested such a set of 17-amino-acid peptides containing the γ-core motif of the antifungal plant defensin MtDef4. These designed peptides exhibited antifungal properties different from those of MtDef4. Focused analysis of a lead peptide, GMA4CG_V6, showed that it was a random coil in solution with little or no secondary structure elements. Additionally, it exhibited potent cation-tolerant antifungal activity against the plant fungal pathogen Botrytis cinerea, the causal agent of grey mould disease in fruits and vegetables. Its multisite MoA involved localization predominantly to the plasma membrane, permeabilization of the plasma membrane, rapid internalization into the vacuole and cytoplasm, and affinity for the bioactive phosphoinositides phosphatidylinositol 3-phosphate (PI3P), PI4P, and PI5P. The sequence motif RRRW was identified as a major determinant of the antifungal activity of this peptide. While topical spray application of GMA4CG_V6 on Nicotiana benthamiana and tomato plants provided preventive and curative suppression of grey mould disease symptoms, the peptide was not internalized into plant cells. Our findings open the possibility that truncated and modified defensin-derived peptides containing the γ-core sequence could serve as promising candidates for further development of bio-inspired fungicides.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1998

Helicity, membrane incorporation, orientation and thermal stability of the large conductance mechanosensitive ion channel from E. coli

In this report, we present structural studies on the large conductance mechanosensitive ion channel (MscL) from E. coli in detergent micelles and lipid vesicles. Both transmission Fourier transform infrared spectroscopy and circular dichroism (CD) spectra indicate that the protein is highly helical in detergents as well as liposomes. The secondary structure of the proteins was shown to be highly resistant towards denaturation (25-95 degrees C) based on an ellipticity thermal profile. Amide H+/D+ exchange was shown to be extensive (ca. 66%), implying that two thirds of the protein are water accessible. MscL, reconstituted in oriented lipid bilayers, was shown to possess a net bilayer orientation using dichroic ratios measured by attenuated total-reflection Fourier transform infrared spectroscopy. Here, we present and discuss this initial set of structural data on this new family of ion-channel proteins.

NASA Discipline Cell Biology↗
DOE OSTI2020

Low-temperature MnBi alloys: Electronic and magnetic properties, constitution, morphology and fabrication (Review article)

The article reviews the rich phenomena of physical properties of MnBi. The diverse phenomena include strong spin-orbit interaction, anomalous temperature dependence of the coercivity and the magneto-crystalline anisotropy field, unique magneto-optical properties. Issues addressed include the nature of the electronic ground states of MnBi, the electronic and magnetic structures, Fermi surface, magneto-crystalline anisotropy, x-ray magnetic dichroism. The discussion includes key experiments, such as optical and magneto-optical spectroscopic measurements, de Haas-van Alphen (dHvA) measurements, x-ray photoemission and x-ray absorption spectroscopy measurements as well as x-ray magnetic circular dichroism. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U were found to be crucial for the Fermi surface, cyclotron masses, magneto-optical properties, and x-ray magnetic circular dichroism. The microscopic origin of unique magneto-crystalline anisotropy and giant Kerr effect in MnBi is analyzed in detail. The huge Kerr effect in MnBi is caused by the combination of a sizable magnetic moment on manganese, the large spin-orbit coupling of bismuth, and a strong hybridization between the manganese 3d and the bismuth 6p states. The magneto-optically active states are mainly the 6p states of Bi. We show that the observed temperature dependence of the magneto-crystalline anisotropy can be explained taking into account the spin-orbit interaction together with strong Coulomb electron-electron interaction. The SO coupling of Bi is equally responsible for the large magneto-crystalline anisotropy energy as is the exchange splitting of Mn. The fabrication, morphology, and constitution of low-temperature MnBi alloys in bulk, thin films, and nanoparticles are discussed. The nanocomposite permanent magnetic materials based on MnBi, (Co, Fe) and Nd 2 Fe 14 B are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Near-infrared C-term MCD spectroscopy of octahedral uranium (V) complexes

C-term magnetic circular dichroism (MCD) spectroscopy is a powerful method for probing d–d and f–f transitions in paramagnetic metal complexes. However, this technique remains underdeveloped both experimentally and theoretically for studies of U(V) complexes of Oh symmetry, which have been of longstanding interest for probing electronic structure, bonding, and covalency in 5f systems. In this study, C-term NIR MCD of the Laporte forbidden f–f transitions of [UCl 6 ] - and [UF 6 ] - are reported, demonstrating the significant fine structure resolution possible with this technique including for the low energy Γ 7 → Γ 8 transitions in [UF 6 ] - . The experimental NIR MCD studies were further extended to [U(OC 6 F 5 ) 6 ] - , [U(CH 2 SiMe 3 ) 6 ] - , and [U(NC(tBu)(Ph)) 6 ] - to evaluate the effects of ligand-type on the f–f MCD fine structure features. Theoretical calculations were conducted to determine the Laporte forbidden f–f transitions and their MCD intensity experimentally observed in the NIR spectra of the U(V) hexahalide complexes, via the inclusion of vibronic coupling, to better understand the underlying spectral fine structure features for these complexes. These spectra and simulations provide an important platform for the application of MCD spectroscopy to this widely studied class of U(V) complexes and identify areas for continued theoretical development.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

State-resolved ultrafast charge and spin dynamics in [Co/Pd] multilayers

We use transient absorption spectroscopy with circularly polarized x rays to detect laser-excited hole states below the Fermi level and compare their dynamics with that of unoccupied states above the Fermi level in ferromagnetic [Co/Pd] multilayers. While below the Fermi level, an instantaneous and significantly stronger demagnetization is observed, above the Fermi level, the demagnetization is delayed by 35 ± 10 fs. This provides a direct visualization of how ultrafast demagnetization proceeds via initial spin-flip scattering of laser-excited holes to the subsequent formation of spin waves.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Nature of the Reactive Biferric Peroxy Intermediate P′ in the Arylamine Oxygenases and Related Binuclear Fe Enzymes

Binuclear nonheme iron enzymes activate O 2 to perform a wide range of chemical transformations. The process of O 2 activation typically involves a biferric peroxy-level intermediate P. It has been previously found that this intermediate undergoes further activation, either protonation or rearrangement to form P′ or further oxidation to form high-valent intermediates Q or X. Here, this study defines the structure of the P′ intermediate in the N-oxygenases CmlI (and AurF based on previous data) using nuclear resonance vibrational spectroscopy (NRVS) in conjugation with density functional theory (DFT) calculations. These results, combined with variable temperature variable field (VTVH) magnetic circular dichroism (MCD) spectroscopy on the 1-electron cryoreduced P′, define the structure of the P′ intermediate as a μ-1,2-hydroxoperoxo biferric site with a second hydroxide bridge. Reaction coordinate calculations demonstrate that single electron transfer (SET) is facilitated by protonation of the peroxo, activating its reductive cleavage, and that the additional hydroxide bridge does not impact this reaction. VTVH MCD studies further reveal that the hydroxide bridge is absent in the biferrous site, suggesting that during the O 2 reaction with the biferrous site, a water molecule forms the hydroxide bridge in providing the proton that activates the peroxide in P′ for reactivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Similarities and Differences in the Effects of Toxic Concentrations of Cadmium and Chromium on the Structure and Functions of Thylakoid Membranes in Chlorella variabilis

Trace metal contaminations in natural waters, wetlands, and wastewaters pose serious threats to aquatic ecosystems—mainly via targeting microalgae. In this work, we investigated the effects of toxic amounts of chromium and cadmium ions on the structure and function of the photosynthetic machinery of Chlorella variabilis cells. To halt the propagation of cells, we used high concentrations of Cd and Cr, 50–50 mg L –1 , in the forms of CdCl 2 x 2.5 H 2 O and K 2 Cr 2 O 7 , respectively. Both treatments led to similar, about 50% gradual diminishment of the chlorophyll contents of the cells in 48 h, which was, however, accompanied by a small (~10%) but statistically significant enrichment (Cd) and loss (Cr) of ß-carotene. Both Cd and Cr inhibited the activity of photosystem II (PSII)—but with more severe inhibitions with Cr. On the contrary, the PsbA (D1) protein of PSII and the PsbO protein of the oxygen-evolving complex were retained more in Cr-treated cells than in the presence of Cd. These data and the higher susceptibility of P700 redox transients in Cr-treated cells suggest that, unlike with Cd, PSII is not the main target in the photochemical apparatus. These differences at the level of photochemistry also brought about dissimilarities at higher levels of the structural complexity of the photosynthetic apparatus. Circular dichroism (CD) spectroscopy measurements revealed moderate perturbations in the macro-organization of the protein complexes—with more pronounced decline in Cd-treated cells than in the cells with Cr. Also, as reflected by transmission electron microscopy and small-angle neutron scattering, the thylakoid membranes suffered shrinking and were largely fragmented in Cd-treated cells, whereas no changes could be discerned with Cr. The preservation of integrity of membranes in Cr-treated cells was most probably aided by high proportion of the de-epoxidized xanthophylls, which were absent with Cd. It can thus be concluded that beside strong similarities of the toxic effects of Cr and Cd, the response of the photosynthetic machinery of C. variabilis to these two trace metal ions substantially differ from each other—strongly suggesting different inhibitory and protective mechanisms following the primary toxic events.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Role of Protein-Water Interface in the Stacking Interactions of Granum Thylakoid Membranes—As Revealed by the Effects of Hofmeister Salts

The thylakoid membranes of vascular plants are differentiated into stacked granum and unstacked stroma regions. The formation of grana is triggered by the macrodomain formation of photosystem II and light-harvesting complex II (PSII-LHCII) and thus their lateral segregation from the photosystem I—light-harvesting complex I (PSI-LHCI) super-complexes and the ATP-synthase; which is then stabilized by stacking interactions of the adjacent PSII-LHCII enriched regions of the thylakoid membranes. The self-assembly and dynamics of this highly organized membrane system and the nature of forces acting between the PSII-LHCII macrodomains are not well understood. By using circular dichroism (CD) spectroscopy, small-angle neutron scattering (SANS) and transmission electron microscopy (TEM), we investigated the effects of Hofmeister salts on the organization of pigment-protein complexes and on the ultrastructure of thylakoid membranes. We found that the kosmotropic agent (NH 4 ) 2 SO 4 and the Hofmeister-neutral NaCl, up to 2 M concentrations, hardly affected the macro-organization of the protein complexes and the membrane ultrastructure. In contrast, chaotropic salts, NaClO 4 , and NaSCN destroyed the mesoscopic structures, the multilamellar organization of the thylakoid membranes and the chiral macrodomains of the protein complexes but without noticeably affecting the short-range, pigment-pigment excitonic interactions. Comparison of the concentration- and time-dependences of SANS, TEM and CD parameters revealed the main steps of the disassembly of grana in the presence of chaotropes. It begins with a rapid diminishment of the long-range periodic order of the grana membranes, apparently due to an increased stacking disorder of the thylakoid membranes, as reflected by SANS experiments. SANS measurements also allowed discrimination between the cationic and anionic effects—in stacking and disorder, respectively. This step is followed by a somewhat slower disorganization of the TEM ultrastructure, due to the gradual loss of stacked membrane pairs. Occurring last is the stepwise decrease and disappearance of the long-range chiral order of the protein complexes, the rate of which was faster in LHCII-deficient membranes. These data are interpreted in terms of a theory, from our laboratory, according to which Hofmeister salts primarily affect the hydrophylic-hydrophobic interactions of proteins, and the stroma-exposed regions of the intrinsic membrane proteins, in particular—pointing to the role of protein-water interface in the stacking interactions of granum thylakoid membranes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Non-Invasive Biophysical Techniques to Monitor the Structural Plasticity of the Photosynthetic Machinery of Live Diatom Cells

The photosynthetic performance of diatoms depends largely on the organization and structural flexibility of their thylakoid membranes, the densely packed, highly organized membrane vesicles in which light reactions of photosynthesis occur. Different regulatory mechanisms that fine tune the photosynthetic functions affect the organization of the photosynthetic machinery at different levels of structural complexity, from the level of individual protein complexes to the macroarray of membrane proteins and the remodeling of the entire thylakoid membrane system. To monitor these reorganizations, non-invasive techniques are of special value. In this chapter, we focus our attention on three of these techniques, which have been demonstrated to provide unique and useful information on the structure and structural and functional plasticity of live diatom cells: (i) circular dichroism (CD) spectroscopy, which has provided unique information on the chiral (macro-)organization of protein complexes and on their rapid, reversible reorganizations, fine-tuning the light-harvesting processes, as well as on variations in the short-range excitonic interactions in the antenna complexes; (ii) small-angle neutron scattering (SANS), which has been used to determine the periodic organization of the thylakoid membranes and to monitor reversible ultrastructural changes on the time-scale of minutes, induced by variations in the environmental conditions such as changes in temperature or light intensity; and (iii) electrochromic shift absorbance transients (ΔA ECS ), a spectroscopic tool which has been shown to be capable of identifying distinct functional groups of the light-harvesting carotenoid fucoxanthin in different diatoms and in cells exposed to different light intensities. Future use of these techniques will most certainly contribute to the deeper understanding of key regulatory mechanisms of photosynthesis in diatoms.

Szabo, Milan↗
DOE OSTI2023

Virus‐Based Pyroelectricity

Abstract The first observation of heat‐induced electrical potential generation on a virus and its detection through pyroelectricity are presented. Specifically, the authors investigate the pyroelectric properties of the M13 phage, which possesses inherent dipole structures derived from the noncentrosymmetric arrangement of the major coat protein (pVIII) with an α‐helical conformation. Unidirectional polarization of the phage is achieved through genetic engineering of the tail protein (pIII) and template‐assisted self‐assembly techniques. By modifying the pVIII proteins with varying numbers of glutamate residues, the structure‐dependent tunable pyroelectric properties of the phage are explored. The most polarized phage exhibits a pyroelectric coefficient of 0.13 µC m −2 °C −1 . Computational modeling and circular dichroism (CD) spectroscopy analysis confirm that the unfolding of α‐helices within the pVIII proteins leads to changes in phage polarization upon heating. Moreover, the phage is genetically modified to enable its pyroelectric function in diverse chemical environments. This phage‐based approach not only provides valuable insights into bio‐pyroelectricity but also opens up new opportunities for the detection of various viral particles. Furthermore, it holds great potential for the development of novel biomaterials for future applications in biosensors and bioelectric materials.

Kim, Han↗
DOE OSTI2023

Genetic Fusion of Thermoresponsive Polypeptides with UCST‐type Behavior Mediates 1D Assembly of Coiled‐Coil Bundlemers

Abstract Thermoresponsive resilin‐like polypeptides (RLPs) of various lengths were genetically fused to two different computationally designed coiled coil‐forming peptides with distinct thermal stability, to develop new strategies to assemble coiled coil peptides via temperature‐triggered phase separation of the RLP units. Their successful production in bacterial expression hosts was verified via gel electrophoresis, mass spectrometry, and amino acid analysis. Circular dichroism (CD) spectroscopy, ultraviolet‐visible (UV/Vis) turbidimetry, and dynamic light scattering (DLS) measurements confirmed the stability of the coiled coils and showed that the thermosensitive phase behavior of the RLPs was preserved in the genetically fused hybrid polypeptides. Cryogenic‐transmission electron microscopy and coarse‐grained modeling revealed that functionalizing the coiled coils with thermoresponsive RLPs leads to their thermally triggered noncovalent assembly into nanofibrillar assemblies.

Patkar, Sai S.↗
DOE OSTI2023

Genetic Fusion of Thermoresponsive Polypeptides with UCST–type Behavior Mediates 1D Assembly of Coiled–Coil Bundlemers

Thermoresponsive resilin-like polypeptides (RLPs) of various lengths were genetically fused to two different computationally designed coiled coil-forming peptides with distinct thermal stability, to develop new strategies to assemble coiled coil peptides via temperature-triggered phase separation of the RLP units. Furthermore, their successful production in bacterial expression hosts was verified via gel electrophoresis, mass spectrometry, and amino acid analysis. Circular dichroism (CD) spectroscopy, ultraviolet-visible (UV/Vis) turbidimetry, and dynamic light scattering (DLS) measurements confirmed the stability of the coiled coils and showed that the thermosensitive phase behavior of the RLPs was preserved in the genetically fused hybrid polypeptides. Cryogenic-transmission electron microscopy and coarse-grained modeling revealed that functionalizing the coiled coils with thermoresponsive RLPs leads to their thermally triggered noncovalent assembly into nanofibrillar assemblies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Improving the bioaccessibility of lipophilic ingredient in its oral intestinal delivery by ultrasound and biological cross‐linker

Abstract BACKGROUND Great efforts have been made to improve the oral bioaccessibility of lipophilic ingredients with multi‐functionalities. Achieving intestinal delivery of lipophilic ingredients and their encapsulation in micelles composed of bile salts and lipid hydrolysates (i.e. fatty acids) is critical for improving oral bioaccessibility. Therefore, oil‐core microcapsules are considered ideal carriers of lipophilic ingredients. Previous studies have reported oil‐core/zein‐shell microcapsules constructed by a one‐step anti‐solvent process. Still, its efficacy as an intestinal delivery system was limited because if the porous shell structure. RESULTS Zein solution was pretreated with ultrasound and tannic acid (TA) cross‐linking. Composite oil‐core microcapsule (COM) with a compact shell structure was successfully prepared by using modified zein solution in the anti‐solvent process. Fourier‐transform infrared spectroscopy and circular dichroism analyses indicated that ultrasound and TA synergistically promote the conformational transition of zein from α‐helix to β‐sheet and enhance the hydrophobic interactions among protein chains. The above changes contribute to the strengthen of shell zein network. Correspondingly, COM presents superior encapsulation efficiency and environmental stability over the simple oil‐core microcapsule (SOM) prepared without the use of ultrasound and TA. Furthermore, antioxidant activity of β‐carotene was well retained during the encapsulation process. In vitro studies indicated that COM was more resistant to digestibility and acid‐induced swelling. More than 87% of β‐carotene could be released in the intestine in a sustainable way. The controllable release behavior thus promoted a significant increase in bioaccessibility of β‐carotene encapsulated in COM compared to SOM (85.9% versus 48.5%). CONCLUSION The COM generated here shows potential for bioaccessibility improvement of lipophilic ingredients. © 2022 Society of Chemical Industry.

Wei, Yun‐Shan↗
DOE OSTI2024

Structural Characterization of Disulfide-Linked p53-Derived Peptide Dimers

Disulfide bonds provide a convenient method for chemoselective alteration of peptide and protein structure and function. We previously reported that mild oxidation of a p53-derived bisthiol peptide (CTFANLWRLLAQNC) under dilute non-denaturing conditions led to unexpected disulfide-linked dimers as the exclusive product. The dimers were antiparallel, significantly α-helical, resistant to protease degradation, and easily reduced back to the original bisthiol peptide. Here, in this work, we examine the intrinsic factors influencing peptide dimerization using a combination of amino acid substitution, circular dichroism (CD) spectroscopy, and X-ray crystallography. CD analysis of peptide variants suggests critical roles for Leu6 and Leu10 in the formation of stable disulfide-linked dimers. The 1.0 Å resolution crystal structure of the peptide dimer supports these data, revealing a leucine-rich LxxLL dimer interface with canonical knobs-into-holes packing. Two levels of higher-order oligomerization are also observed in the crystal: an antiparallel “dimer of dimers” mediated by Phe3 and Trp7 residues in the asymmetric unit and a tetramer of dimers mediated by Trp7 and Leu10. In CD spectra of Trp-containing peptide variants, minima at 227 nm provide evidence for the dimer of dimers in dilute aqueous solution. Importantly, and in contrast to the original dimer model, the canonical leucine-rich core and robust dimerization of most peptide variants suggests a tunable molecular architecture to target various proteins and evaluate how folding and oligomerization impact various properties, such as cell permeability.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Dirigent isoflavene-forming PsPTS2: 3D structure, stereochemical, and kinetic characterization comparison with pterocarpan-forming PsPTS1 homolog in pea

Pea (legume plant defense) phytoalexin pterocarpans (–)-maackiain and (+)-pisatin have opposite C6a and C11a configurations, but how this occurs biosynthetically is unknown. Herein, pea dirigent-protein (DP) PsPTS2, which generates 7,2'-dihydroxy-4',5'-methylenedioxyisoflav-3-ene (DMDIF), was investigated as regards stereoselectivity towards four possible 7,2'-dihydroxy-4',5'-methylenedioxyisoflavan-4-ol (DMDI) stereoisomers. Each DMDI stereoisomer configuration was determined using NMR spectroscopy, electronic circular dichroism, and molecular orbital analyses. PsPTS2 efficiently converted cis-(3R,4R)-DMDI into DMDIF, this being 20-fold faster than with the trans-(3R,4S)-isomer. The 4R-configured substrate’s near ß-axial OH orientation significantly enhanced its leaving group abilities in creating intermediate A-ring mono-quinone methide (QM), whereas the 4S-isomer’s 4-OH group α-equatorial orientation was a poorer leaving group. Substrate docking simulations also indicated that the 4R-configured ß-axial OH was closest to the Asp catalytic center, whereas the 4S-isomer’s α-equatorial OH was further away. Neither cis-(3S,4S)- nor trans-(3S, 4R)-DMDIs were substrates, even with the former having the same C3/C4 stereochemistry as (+)-pisatin. PsPTS2, assayed with cis-(3R,4R)-7,2'-dihydroxy-4'-methoxyisoflavan-4-ol [cis-(3R,4R)-DMI] and its C3/C4 stereoisomers, gave 2',7-dihydroxy-4'-methoxyisoflav-3-ene (DMIF), with the same substrate stereoselectivity. DP homologs may exist in licorice (Glycyrrhiza pallidiflora) and the tree legume Bolusanthus speciosus, as DMIF is found in both. PsPTS1 preferentially utilized cis-(3R,4R)-DMDI to give (–)-maackiain, this being 2200-fold more efficient than with cis-(3R,4R)-DMI. PsPTS1 also slowly converted trans-(3S,4R)-DMDI into (+)-maackiain, again reflecting the better 4R configured OH leaving group. Pea PsPTS2 and PsPTS1 provisionally provide a facile DP-engendered means to enable differing C6a and C11a configurations in (+)-pisatin and (–)-maackiain. Both DP transformations are considered to occur via DP-engendered generation of an identical mono-QM bound intermediate, which with PsPTS2 either re-aromatizes to give DMDIF or with PsPTS1 undergoes intramolecular cyclization to afford (–)-maackiain. Substrate docking simulations using PsPTS2 (2.5 Å resolution) and PsPTS1 (1.5 Å resolution) plausibly indicate that cis-(3R,4R)-DMDI binds in the anti-configuration in the PsPTS2 active site to afford DMDIF, and the syn-configuration in PsPTS1 to give maackiain.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Hyperfusogenic Mutations Destabilize the Postfusion Six-Helix Bundle of the Measles Virus Fusion Glycoprotein

Fusion of the host membrane and viral envelope by class I viral fusion proteins is driven by the assembly of a postfusion six-helix bundle formed through antiparallel interactions between N-terminal (HR1) and C-terminal (HR2) heptad-repeat regions. Although mutations in these regions of the measles virus (MeV) fusion (F) glycoprotein are known to promote neuropathogenic and hyperfusogenic phenotypes, their effects on postfusion core stability have not been systematically examined. Here, we combine peptide biophysics and X-ray crystallography to interrogate how mutations within the HR2 domain, present in native neuropathogenic MeV isolates (e.g., L454W and N462K) and laboratory-generated hyperfusogenic variants (e.g., L454M and T461A), influence postfusion 6HB assembly. Circular dichroism (CD) spectroscopy reveals that, with few exceptions, these mutations decrease postfusion core stability, despite their association with enhanced fusion activity. We also report the first crystal structure of the wild-type MeV postfusion core as well as structures of six hyperfusogenic variants, enabling high-resolution comparison of the molecular basis of destabilization. Structural analysis shows that these effects arise from localized perturbations to steric packing, hydrogen bonding networks, and helix-stabilizing interactions within HR2, while the overall 6HB architecture remains conserved. Together, these results indicate that hyperfusogenic mutations are not associated with stabilization of the postfusion state and are instead consistent with models in which hyperfusogenicity arises from a reduction in the energetic barrier to fusion, potentially through effects on prefusion stability or triggering efficiency. These findings establish key sequence-structure–stability relationships governing coiled-coil assembly and provide a framework for the design of HR1- and HR2-based fusion inhibitors.

Genetics↗
DOE OSTI2022

Donor–Acceptor Conjugated Copolymers Containing Transition-Metal Complex: Intrachain Magnetic Exchange Interactions and Magneto-Optical Activity

A donor-acceptor conjugated copolymer containing thienothiophene (TT) (Donor) units and Co(II) complexes (Acceptor) has been synthesized and characterized. The studies of magnetic properties of the polymers by SQUID and EPR measurements showed antiferromagnetic exchange interaction between neighboring spin centers along with the polymer backbone through intrachain in-teractions. It is the first time that D-A conjugated polymer backbone serving as bridging ligands for magnetic couplings, making this type of polymers promising as magnetic materials. Moreover, the magneto-optical activity (MOA) of polymer LCP1 was char-acterized using magnetic circular dichroism (MCD) spectroscopy. It was found that the material exhibits a large magneto-optic rotation with a peak Verdet constant of 2980 deg*T -1 *m -1 at 590 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Molecular Dynamical and Quantum Mechanical Exploration of the Site-Specific Dynamics of Cy3 Dimers Internally Linked to dsDNA

Performing spectroscopic measurements on biomolecules labeled with fluorescent probes is a powerful approach to locating the molecular behavior and dynamics of large systems at specific sites within their local environments. The indocarbocyanine dye Cy3 has emerged as one of the most commonly used chromophores. The incorporation of Cy3 dimers into DNA enhances experimental resolution owing to the spectral characteristics influenced by the geometric orientation of excitonically coupled monomeric units. Various theoretical models and simulations have been utilized to aid in the interpretation of the experimental spectra. In this study, we employ all-atom molecular dynamics simulations to study the structural dynamics of Cy3 dimers internally linked to the dsDNA backbone. We used quantum mechanical calculations to derive insights from both the linear absorption spectra and the circular dichroism data. Furthermore, we explore potential limitations within a commonly used force field for cyanine dyes. The molecular dynamics simulations suggest the presence of four possible Cy3 dimeric populations. The spectral simulations on the four populations show one of them to agree better with the experimental signatures, suggesting it to be the dominant population. Furthermore, the relative orientation of Cy3 in this population compares very well with previous predictions from the Holstein–Frenkel Hamiltonian model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗