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At least 1,081 records · Page 60

Allosteric prediction via convolutional neural networks and protein structural and dynamical features

Allostery is the phenomenon whereby a binding event or covalent modification at one site in a protein modulates function at a distal site, thus changing a protein’s functional state. As such, it is a ubiquitous aspect of protein functional regulation. Computationally predicting allosteric states is important as part of the broader challenge of functional annotation, but it also has practical implications for drug development, as targeting an allosteric site often affords greater specificity compared with targeting an orthosteric site. This study introduces a machine learning approach to predict the allosteric functional state using the small G-protein KRas as the model system, due to its implication in many types of cancer and being well studied as a result with many x-ray crystallographic structures of KRas available with different mutations and ligands bound. Using structural and dynamical features that can be cast as images, namely interatomic distances, contact maps, covariance, and mutual information, supervised learning was performed using convolutional neural networks. Two pretrained convolutional neural network architectures, GoogLeNet and ResNet18, were fine-tuned to classify KRas into active or inactive states based on these features. Across training regimes, atomic contact maps emerged as the most effective structural feature, whereas linearized mutual information outperformed covariance in capturing dynamical correlations relevant to allostery. Models achieved significant validation accuracy, with atomic contact maps yielding up to 90% accuracy. In conclusion, the findings suggest that integrating global structural rearrangements and correlated motion patterns with deep learning can reliably predict protein allosteric states, offering a promising framework for understanding allosteric regulation and developing targeted therapeutics.

Rajeshwar T., Rajitha [Oak Ridge National Laborato↗

A unified multigrid solver for the Navier-Stokes equations on mixed element meshes

A unified multigrid solution technique is presented for solving the Euler and Reynolds-averaged Navier-Stokes equations on unstructured meshes using mixed elements consisting of triangles and quadrilaterals in two dimensions, and of hexahedra, pyramids, prisms, and tetrahedra in three dimensions. While the use of mixed elements is by no means a novel idea, the contribution of the paper lies in the formulation of a complete solution technique which can handle structured grids, block structured grids, and unstructured grids of tetrahedra or mixed elements without any modification. This is achieved by discretizing the full Navier-Stokes equations on tetrahedral elements, and the thin layer version of these equations on other types of elements, while using a single edge-based data-structure to construct the discretization over all element types. An agglomeration multigrid algorithm, which naturally handles meshes of any types of elements, is employed to accelerate convergence. An automatic algorithm which reduces the complexity of a given triangular or tetrahedral mesh by merging candidate triangular or tetrahedral elements into quadrilateral or prismatic elements is also described. The gains in computational efficiency afforded by the use of non-simplicial meshes over fully tetrahedral meshes are demonstrated through several examples.

Mavriplis, D. J.↗

The effects of particle loading on turbulence structure and modelling

The objective of the present research was to extend the Direct Numerical Simulation (DNS) approach to particle-laden turbulent flows using a simple model of particle/flow interaction. The program addressed the simplest type of flow, homogeneous, isotropic turbulence, and examined interactions between the particles and gas phase turbulence. The specific range of problems examined include those in which the particle is much smaller than the smallest length scales of the turbulence yet heavy enough to slip relative to the flow. The particle mass loading is large enough to have a significant impact on the turbulence, while the volume loading was small enough such that particle-particle interactions could be neglected. Therefore, these simulations are relevant to practical problems involving small, dense particles conveyed by turbulent gas flows at moderate loadings. A sample of the results illustrating modifications of the particle concentration field caused by the turbulence structure is presented and attenuation of turbulence by the particle cloud is also illustrated.

Squires, Kyle D.↗

Development of flame resistant treatment for Nomex fibrous structures

Flame resistant fibrous materials for space shuttle application were developed through chemical modification of commercially available aromatic polyamide fibrous products. The new surface treatment was achieved in the laboratory by ultraviolet activation of the fabric in the presence of fluoroolefin monomers and a diluent gas. The monomers grafted under these conditions provide the improved properties of the fabric in flame resistance, chemical inertness, and nonwettability without the sacrifice of color or physical properties. The laboratory reaction vessel was scaled-up to a batch continuous process, which treats ten yards of the commercial width textiles. The treated commercial width Nomex (HT-10-41) from the scaled-up reactor is self-extinguishing in an oxygen-enriched environment, water-repellent, soft, silky, and improved in chemical resistance. Unlike most textile processes, the grafting unit operates under dry conditions and no chemical by-products have to be washed out of the finished product.

Toy, M. S.↗

Enzymatic reconstitution of ribosomal peptide backbone thioamidation

Methyl-coenzyme M reductase (MCR) is an essential enzyme found strictly in methanogenic and methanotrophic archaea. MCR catalyzes a reversible reaction involved in the production and consumption of the potent greenhouse gas methane. The α-subunit of this enzyme (McrA) contains several unusual posttranslational modifications, including the only known naturally occurring example of protein thioamidation. We have recently demonstrated by genetic deletion and mass spectrometry that the tfuA and ycaO genes of Methanosarcina acetivorans are involved in thioamidation of Gly465 in the MCR active site. Modification to thioGly has been postulated to stabilize the active site structure of MCR. Herein, we report the in vitro reconstitution of ribosomal peptide thioamidation using heterologously expressed and purified YcaO and TfuA proteins from M. acetivorans . Like other reported YcaO proteins, this reaction is ATP-dependent but requires an external sulfide source. We also reconstitute the thioamidation activity of two TfuA-independent YcaOs from the hyperthermophilic methanogenic archaea Methanopyrus kandleri and Methanocaldococcus jannaschii . Using these proteins, we demonstrate the basis for substrate recognition and regioselectivity of thioamide formation based on extensive mutagenesis, biochemical, and binding studies. Finally, we report nucleotide-free and nucleotide-bound crystal structures for the YcaO proteins from M. kandleri . Sequence and structure-guided mutagenesis with subsequent biochemical evaluation have allowed us to assign roles for residues involved in thioamidation and confirm that the reaction proceeds via backbone O -phosphorylation. We conclude these data assign a new biochemical reaction to the YcaO superfamily and paves the way for further characterization of additional peptide backbone posttranslational modifications.

59 BASIC BIOLOGICAL SCIENCES↗

Findings of the Joint Workshop on Evaluation of Impacts of Space Station Freedom Ground Configurations

A workshop to consider the effects of various proposed Space Station Freedom (SSF) grounding schemes was held. Expert from the plasma interactions community evaluated the impacts of environmental interactions on SSF under each of three proposed grounding schemes. The choice of the grounding scheme for the SSF power system was found to have important implications for SSF design. Interactions of the SSF power system and structure with the low earth orbit (LEO) plasma differ significantly between different grounding schemes. Environmental constraints will require modification of current SSF designs under any grounding scheme. Maintaining the present negative ground scheme may compromise SSF safety, structural integrity, and electromagnetic compatibility, and will increase contamination rates over alternate schemes. Positive grounding of the array requires redesign of the primary power system. Floating the array reduces the number of circuit changes in the primary power system but adds new hardware. Maintaining the present design will affect all parts of SSF. However, no impacts were identified on SSF systems outside of the electrical power system by positively grounding or floating the array.

Ferguson, Dale C.↗

30S subunit recognition and G1405 modification by the aminoglycoside-resistance 16S ribosomal RNA methyltransferase RmtC

Acquired ribosomal RNA (rRNA) methylation has emerged as a significant mechanism of aminoglycoside resistance in pathogenic bacterial infections. Modification of a single nucleotide in the ribosome decoding center by the aminoglycoside-resistance 16S rRNA (m 7 G1405) methyltransferases effectively blocks the action of all 4,6-deoxystreptamine ring-containing aminoglycosides, including the latest generation of drugs. To define the molecular basis of 30S subunit recognition and G1405 modification by these enzymes, we used a S-adenosyl-L-methionine analog to trap the complex in a postcatalytic state to enable determination of a global 3.0 Å cryo-electron microscopy structure of the m 7 G1405 methyltransferase RmtC bound to the mature Escherichia coli 30S ribosomal subunit. This structure, together with functional analyses of RmtC variants, identifies the RmtC N-terminal domain as critical for recognition and docking of the enzyme on a conserved 16S rRNA tertiary surface adjacent to G1405 in 16S rRNA helix 44 (h44). To access the G1405 N7 position for modification, a collection of residues across one surface of RmtC, including a loop that undergoes a disorder-to order transition upon 30S subunit binding, induces significant distortion of h44. This distortion flips G1405 into the enzyme active site where it is positioned for modification by two almost universally conserved RmtC residues. Further, these studies expand our understanding of ribosome recognition by rRNA modification enzymes and present a more complete structural basis for future development of strategies to inhibit m 7 G1405 modification to resensitize bacterial pathogens to aminoglycosides.

59 BASIC BIOLOGICAL SCIENCES↗

Multifunctional Polymers and Composites for Aerospace Applications

System needs and challenges for commercial aviation and space exploration are constantly changing. Multifunctional materials are ideal for aerospace applications because their integration into structural components has potential to not only improve efficiency, but it can also increase payload and mission capabilities without the burden of significant additions to mass and volume. Multi-constituent materials will play an important role in enabling structures with the potential to demonstrate true multi-functionality; however, modifications to many mature polymer processing methods may be necessary. This presentation will cover multifunctional materials development efforts underway at the NASA Glenn Research Center related to formulating and characterizing novel electrical insulation for high voltage aircraft. Incorporating functionality into the reinforcement material is another materials development technique that will be discussed, which includes braiding with hybrid fibers to enhance toughness in composite structures, stitching with carbon nanotube yarns to make durable electrically conductive textiles, and treating fabrics with shear thickening fluid suspensions to produce impact-resistant inflatable habitats.

multi-functional composites↗

Confronting Domain Shift in Trained Neural Networks

Neural networks (NNs) are known as universal function approximators and can interpolate nonlinear functions between observed data points. However, when the target domain for deployment shifts from the training domain and NNs must extrapolate, the results are notoriously poor. Prior work Martinez et al. (2019) has shown that NN uncertainty estimates can be used to correct binary predictions in shifted domains without retraining the model. We hypothesize that this approach can be extended to correct real-valued time series predictions. As an exemplar, we consider two mechanical systems with nonlinear dynamics. The first system consists of a spring-mass system where the stiffness changes abruptly, and the second is a real experimental system with a frictional joint that is an open challenge for structural dynamicists to model efficiently. Our experiments will test whether 1) NN uncertainty estimates can identify when the input domain has shifted from the training domain and 2) whether the information used to calculate uncertainty estimates can be used to correct the NN’s time series predictions. While the method as proposed did not significantly improve predictions, our results did show potential for modifications that could improve models’ predictions and play a role in structural health monitoring systems that directly impact public safety.

97 MATHEMATICS AND COMPUTING↗

An Investigation of Process Parameter Modifications on Additively Manufactured Inconel 718 Parts

Additive manufacturing (AM) allows for the fabrication of complex parts via layer-by-layer melting of metal powder. Laser powder-bed AM processes use a variety of process parameters including beam power, beam velocity, and hatch spacing to control melting. Alterations to these parameters have often been attempted to reduce porosity, for example, but less work has been done to on comprehensive effects of process parameter modifications. This study looks at the effects of altering these parameters on microstructure, porosity, and mechanical performance of Inconel 718. The results showed that process parameter modifications that result in porosity formation can significantly reduce fatigue life, while microstructure changes were minimal and had little effect on tensile properties. The precipitate structure was not found to be changed significantly. These results can inform future process parameter modifications, as well as heat treatments to optimize mechanical properties.

36 MATERIALS SCIENCE↗

Pseudouridinylation of mRNA coding sequences alters translation

Chemical modifications of RNAs have long been established as key modulators of nonprotein-coding RNA structure and function in cells. There is a growing appreciation that messenger RNA (mRNA) sequences responsible for directing protein synthesis can also be posttranscriptionally modified. The enzymatic incorporation of mRNA modifications has many potential outcomes, including changing mRNA stability, protein recruitment, and translation. In this work, we tested how one of the most common modifications present in mRNA coding regions, pseudouridine (Ψ), impacts protein synthesis using a fully reconstituted bacterial translation system and human cells. Our work reveals that replacing a single uridine nucleotide with Ψ in an mRNA codon impedes amino acid addition and EF-Tu GTPase activation. A crystal structure of the Thermus thermophilus 70S ribosome with a tRNA Phe bound to a ΨUU codon in the A site supports these findings. We also find that the presence of Ψ can promote the low-level synthesis of multiple peptide products from a single mRNA sequence in the reconstituted translation system as well as human cells, and increases the rate of near-cognate Val-tRNA Val reacting on a ΨUU codon. The vast majority of Ψ moieties in mRNAs are found in coding regions, and our study suggests that one consequence of the ribosome encountering Ψ can be to modestly alter both translation speed and mRNA decoding.

59 BASIC BIOLOGICAL SCIENCES↗

Neutron stars structure in the context of massive gravity

Motivated by the recent interests in spin−2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

79 ASTRONOMY AND ASTROPHYSICS↗

Wing design for a civil tiltrotor transport aircraft

The goal of this research is the proper tailoring of the civil tiltrotor's composite wing-box structure leading to a minimum-weight wing design. With focus on the structural design, the wing's aerodynamic shape and the rotor-pylon system are held fixed. The initial design requirement on drag reduction set the airfoil maximum thickness-to-chord ratio to 18 percent. The airfoil section is the scaled down version of the 23 percent-thick airfoil used in V-22's wing. With the project goal in mind, the research activities began with an investigation of the structural dynamic and aeroelastic characteristics of the tiltrotor configuration, and the identification of proper procedures to analyze and account for these characteristics in the wing design. This investigation led to a collection of more than thirty technical papers on the subject, some of which have been referenced here. The review of literature on the tiltrotor revealed the complexity of the system in terms of wing-rotor-pylon interactions. The aeroelastic instability or whirl flutter stemming from wing-rotor-pylon interactions is found to be the most critical mode of instability demanding careful consideration in the preliminary wing design. The placement of wing fundamental natural frequencies in bending and torsion relative to each other and relative to the rotor 1/rev frequencies is found to have a strong influence on the whirl flutter. The frequency placement guide based on a Bell Helicopter Textron study is used in the formulation of frequency constraints. The analysis and design studies are based on two different finite-element computer codes: (1) MSC/NASATRAN and (2) WIDOWAC. These programs are used in parallel with the motivation to eventually, upon necessary modifications and validation, use the simpler WIDOWAC code in the structural tailoring of the tiltrotor wing. Several test cases were studied for the preliminary comparison of the two codes. The results obtained so far indicate a good overall agreement between the two codes.

Rais-Rohani, Masoud↗

Residual flexibility test method for verification of constrained structural models

A method is presented for deriving constrained modes and frequencies from a model correlated to a set of free-free test modes and a set of measured residual flexibilities. The method involves a simple modification of the MacNeal and Rubin component mode representation to allow verification of a constrained structural model. Results for two spaceflight structures show quick convergence of constrained modes using an easily measurable set of free-free modes plus the residual flexibility matrix or its boundary partition. This paper further validates the residual flexibility approach as an alternative test/analysis method when fixed-base testing proves impractical.

Admire, John R.↗

Findings of the Joint Workshop on Evaluation of Impacts of Space Station Freedom Ground Configurations

At the workshop, experts from the plasma interactions community evaluated the impacts of environmental interactions on the Space Station Freedom (SSF) under each of the proposed grounding schemes. The grounding scheme chosen for the SSF power system was found to have serious implications for SSF design. Interactions of the SSF power system and structure with the low Earth orbit (LEO) plasma differ significantly between different proposed grounding schemes. Environmental constraints will require modification of current SSF designs under any grounding scheme. Maintaining the present negative-grounding scheme compromises SSF safety, structural integrity, and electromagnetic compatibility. It also will increase contamination rates over alternative grounding schemes. One alternative, positive grounding of the array, requires redesign of the primary power system in work package four. Floating the array reduces the number of circuit changes to work package four but adds new hardware. Maintaining the current design will affect all work packages; however, no impacts were identified on work packages one, two, or three by positively grounding or floating the array, with the possible exception of extra corona protection in multi-wire connectors.

Ferguson, Dale C.↗

Use of lightweight composites for GAS payload structures

A key element in the design of a small self-contained payload is the supporting structure. This structure must support the experiments and other components while using as little space and weight as possible. Hence, the structure material must have characteristics of being both strong and light. Aluminum was used for the structure on the first Purdue University payload, but consumed a relatively large percentage of the total payload weight. The current payload has a larger power supply requirement than did the previous payload. To allow additional weight for the batteries, a composite material has been chosen for the structure which has the required strength while being considerably lighter than aluminum. A radial fin design has been chosen for ease of composite material lay-up and its overall strength of design. A composite plate will connect the free ends of the fins and add strength and reduce vibration. The physical characteristics of the composite material and the method of open lay-up construction is described. Also discussed are the testing, modifications, and problems encountered during assembly of the experiments to the structure.

Spencer, Mark B.↗

Novel Amorphous Carbons for the Adsorption of Phosphate: Part I. Elucidation of Chemical Structure of N-Metal-Doped Chars

Due to phosphate’s necessity in agriculture and its danger to the environment, the development of adsorbents for its removal has been the subject of intensive research activity. Although the introduction of nitrogen functionality to chars and modification of biochar with metals have proven to change the character of the char structure, making it more active toward nutrients, there is no study regarding the doping of biochar with metals and nitrogen simultaneously for the adsorption of phosphates. This paper is the first of two in which we report the production, characterization, and evaluation of N-metal-doped biochars from cellulose for phosphate removal from liquid effluents. In this part, we describe the production and characterization of N-Ca-, N-Fe-, and N-Mg-doped biochars. The elemental composition and surface area of each of the materials produced is reported. Elemental and surface characterization of the chars are reported with the largest N content appearing at a temperature of 800 °C (12.5 wt %) and a maximum surface area for biochar produced at 900 °C (1314 m2/g). All of the adsorbents were visualized by scanning electron microscope (SEM), confirming that although there are some crystals on the surface of the biochar produced, most of the N, Mg, and Ca are part of the polyaromatic ring structure. Transmission electron microscope (TEM) images clearly show the formation of nanoclusters with the metals in the case of N-Fe and N-Ca biochars. The N-Mg biochars show a uniform distribution of the Mg through the carbon surface. X-ray photoelectron spectroscopy (XPS) studies of the biochars produced with metals and varying nitrogen levels clearly show Mg and Ca peaks shifting their position in the presence of N, suggesting the formation of stable structures between metals and N in the carbon polyaromatic ring system. To elucidate the nature of these structures, we conducted DFT-based calculations on different configurations of the nitrogenated structures. The calculated binding energy shifts were found to closely match the XPS experimental binding energy, confirming the likelihood of these structures in biochar. Finally, based on our experimental and modeling results, we hypothesize that an important fraction of the Mg and Ca is introduced to these biochars at the edges. Another fraction of Mg and Ca is in the form of phthalocyanine-like internal structures. More experimental studies are needed to confirm the formation of these very interesting structures and their potential use as adsorbents or catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

A divergent synthetic route to functional copolymer libraries via modular polymers

High-throughput polymer synthesis enables rapid exploration of chemical space but remains limited by batch-to-batch inconsistencies that can obscure structure–property relationship trends. To address this challenge, we developed a synthetic approach to produce multifunctional copolymers using post-polymerization modification of activated ester modular polymers with commercially available amines. Easily derivitized parent polymers—poly(tetrafluorophenyl acrylate) and poly(tetrafluorophenyl styrene sulfonate)—were synthesized by RAFT polymerization to yield single polymer batches containing highly reactive tetrafluorophenyl esters or sulfonate esters on each repeat unit. Tuning post-polymerization modification reaction conditions enabled the addition of sub-stoichiometric amounts of amines (relative to the repeat unit) to yield partially functionalized intermediates that could then be further derivatized. Reaction monitoring by 19 F NMR spectroscopy confirmed good control over these sequential post-polymerization modifications. This synthetic route produced a variety of copolymers with defined comonomer ratios while preserving the underlying polymer structure (degree of polymerization, dispersity, tacticity) for both the acrylate and styrene sulfonate backbones. We further applied this approach in a divergent manner to create a small library of structurally distinct copolymers from a single parent batch in three synthetic steps. This modular, divergent synthesis demonstrates a general route to structurally consistent copolymer libraries that enable systematic studies of structure–property relationships and can accelerate functional materials discovery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗