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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.

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At least 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Cryo-EM structure of RNA-induced tau fibrils reveals a small C-terminal core that may nucleate fibril formation

In neurodegenerative diseases including Alzheimer’s and amyotrophic lateral sclerosis, proteins that bind RNA are found in aggregated forms in autopsied brains. Evidence suggests that RNA aids nucleation of these pathological aggregates; however, the mechanism has not been investigated at the level of atomic structure. Here, we present the 3.4-Å resolution structure of fibrils of full-length recombinant tau protein in the presence of RNA, determined by electron cryomicroscopy (cryo-EM). The structure reveals the familiar in-register cross-β amyloid scaffold but with a small fibril core spanning residues Glu391 to Ala426, a region disordered in the fuzzy coat in all previously studied tau polymorphs. RNA is bound on the fibril surface to the positively charged residues Arg406 and His407 and runs parallel to the fibril axis. The fibrils dissolve when RNase is added, showing that RNA is necessary for fibril integrity. While this structure cannot exist simultaneously with the tau fibril structures extracted from patients’ brains, it could conceivably account for the nucleating effects of RNA cofactors followed by remodeling as fibrils mature.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

The structure of the Thermococcus gammatolerans McrB N-terminal domain reveals a new mode of substrate recognition and specificity among McrB homologs

McrBC is a two-component, modification-dependent restriction system that cleaves foreign DNA-containing methylated cytosines. Previous crystallographic studies have shown that Escherichia coli McrB uses a base-flipping mechanism to recognize these modified substrates with high affinity. The side chains stabilizing both the flipped base and the distorted duplex are poorly conserved among McrB homologs, suggesting that other mechanisms may exist for binding modified DNA. In this paper we present the structures of the Thermococcus gammatolerans McrB DNA-binding domain (TgΔ185) both alone and in complex with a methylated DNA substrate at 1.68 and 2.27 Å resolution, respectively. The structures reveal that TgΔ185 consists of a YT521-B homology (YTH) domain, which is commonly found in eukaryotic proteins that bind methylated RNA and is structurally unrelated to the E. coli McrB DNA-binding domain. Structural superposition and co-crystallization further show that TgΔ185 shares a conserved aromatic cage with other YTH domains, which forms the binding pocket for a flipped-out base. Mutational analysis of this aromatic cage supports its role in conferring specificity for the methylated adenines, whereas an extended basic surface present in TgΔ185 facilitates its preferential binding to duplex DNA rather than RNA. Together, these findings establish a new binding mode and specificity among McrB homologs and expand the biological roles of YTH domains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Theory of oblique-field magnetoresistance from spin centers in three-terminal spintronic devices

Here, we present a general stochastic Liouville theory of electrical transport across a barrier between two conductors that occurs via sequential hopping through a single defect's spin-0 to spin-1/2 transition. We find magnetoconductances similar to Hanle features (pseudo Hanle features) that originate from Pauli blocking without spin accumulation, and also predict that evolution of the defect's spin modifies the conventional Hanle response, producing an inverted Hanle signal from spin center evolution. We propose studies in oblique magnetic fields that would unambiguously determine if a magnetoconductance results from spin-center assisted transport.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Determination of rutile transition metal oxide (110) surface terminations by scanning tunneling microscopy contrast reversal

The surfaces of rutile transition-metal oxides (TMO 2 ) are widely investigated for catalysis, photoelectrochemical solar cells, memristors, and supercapacitors, but their structures have remained controversial. Here we employ density functional theory to predict that a universal behavior of metallic TMO 2 surfaces, i.e., the stoichiometric TMO 2 surfaces, exhibit a contrast reversal in simulated scanning tunneling microscopy (STM) images at different scanning biases. The predictions are verified by experimental STM imaging of RuO 2 (110) surfaces and this feature is shown to enable accurate determinations of the TMO 2 (110) surface structures under various conditions. This research provides different insights into the electronic properties of TMO 2 (110) surfaces and offers an effective method to directly map the surface structure and point defects using bias-dependent STM.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗