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Tethering complex

Jie Xu, Peter Wipf
A Pd(0)-catalyzed elimination of an allylic acetate generates a π-allyl complex that is postulated to initiate a novel intramolecular Diels-Alder cycloaddition to a tethered furan (IMDAF). Under the reaction conditions, this convergent, microwave-accelerated cascade process provides substituted indoles in moderate to good yields after Pd-hydride elimination, aromatization by dehydration, and in situ N-Boc cleavage.
August 16, 2017: Organic & Biomolecular Chemistry
Seung-Yeol Baek, Takashi Kurogi, Dahye Kang, Masahiro Kamitani, Seongyeon Kwon, Douglas Solowey, Chun-Hsing Chen, Maren Pink, Patrick J Carroll, Daniel J Mindiola, Mu-Hyun Baik
The complex (PNP)Ti=CHtBu(CH2tBu) (PNP = N[2-PiPr2-4-methylphenyl]2-) dehydrogenates cyclohexane to cyclohexene by forming a transient low-valent titanium-alkyl species, [(PNP)Ti(CH2tBu)], which reacts with two equivalents of quinoline (Q) at room temperature to form H3CtBu and a Ti(IV) species where the less hindered C2=N1 bond of Q is ruptured and coupled to another equivalent of Q. The product isolated from this reaction is an imide with a tethered cycloamide group, (PNP)Ti=N[C18H13N] (1). Under photolytic conditions, intramolecular C-H bond activation across the imide-moiety in 1 occurs to form 2, and thermolysis reverses this process...
August 16, 2017: Journal of the American Chemical Society
Hua Guo, Yana Kazadaeva, Fabian E Ortega, Manjunath N Swamy, Tushar J Desai
GW182 (also known asTNRC6) family members are critically involved in the final effector phase of miRNA-mediated mRNA repression. The three mammalian paralogs, TNRC6a, b and c, are thought to be redundant based on Argonaute (Ago) binding, tethering assays, and RNAi silencing of individual members in cell lines. To test this idea, we generated TNRC6a, b and c knockout mice. TNRC6a mutants die at mid-gestation, while b- and c- deleted mice are born at a Mendelian ratio. However, the majority of TNRC6b and all TNRC6c mutants die within 24 hours after birth, the latter with respiratory failure...
August 12, 2017: Developmental Biology
Yaakov Levy
Proteins, similarly to other biomolecules, have a modular and hierarchical structure. Various building blocks serve to construct proteins of high structural complexity and diverse functionality. In multi-domain proteins, for example, domains are fused to each other in different combinations to achieve different functions. Although the LEGO bricks metaphor is justified as a means of simplifying the complexity of 3-dimensional protein structures, several fundamental properties (such as allostery or the induced-fit mechanism) make deviation from it necessary to respect the plasticity, softness, and cross-talks that are essential to protein function...
August 15, 2017: Biochemistry
Christoph Kaub, Sergei Lebedkin, Sebastian Bestgen, Ralf Köppe, Manfred M Kappes, Peter W Roesky
To force metal ions in heterometallic coinage metal complexes into preset compartments, we have synthesized a ligand with two N-heterocyclic carbenes (NHCs) separated by a methylene bridge and two bipyridine moieties tethered to each NHC moiety. By using this ligand, tetranuclear heterodimetallic gold/copper and gold/silver complexes were obtained. These complexes show an unprecedented V-shape or linear MAu2M (M = Cu, Ag) configuration in the solid state. The photophysical properties of the new compounds are significantly affected by the complexed metal ions...
August 15, 2017: Chemical Communications: Chem Comm
Christophe Lefebvre, Renaud Legouis, Emmanuel Culetto
ESCRT (endosomal sorting complex required for transport) machinery has been initially identified for its role during endocytosis, which allows membrane proteins and lipids to be degraded in the lysosome. ESCRT function is required to form intraluminal vesicles permitting internalization of cytosolic components or membrane embedded cargoes and promoting endosome maturation. ESCRT machinery also contributes to multiple key cell mechanisms in which it reshapes membranes. In addition, ESCRT actively participates in different types of autophagy processes for degrading cytosolic components, such as endosomal microautophagy and macroautophagy...
August 11, 2017: Seminars in Cell & Developmental Biology
James E Byers, Zachary C Holmes, Jennafer C Malek
Although cascading effects of top predators can help structure communities, their influence may vary across habitats that differentially protect prey. Therefore, to understand how and to what degree habitat complexity can affect trophic interactions in adjacent habitats, we used a combination of a broad regional-scale survey, manipulative field trials, and an outdoor mesocosm experiment to quantify predator-prey interaction strengths across four trophic levels. Within estuaries of the southeastern USA, bonnethead sharks (Sphyrna tiburo) hunt blue crabs on mudflats and adjacent oyster reefs, two habitats with vastly different aboveground structure...
August 12, 2017: Oecologia
Azuma Taoka, Ayako Kiyokawa, Chika Uesugi, Yousuke Kikuchi, Zachery Oestreicher, Kaori Morii, Yukako Eguchi, Yoshihiro Fukumori
Magnetotactic bacteria are a unique group of bacteria that synthesize a magnetic organelle termed the magnetosome, which they use to assist with their magnetic navigation in a specific type of bacterial motility called magneto-aerotaxis. Cytoskeletal filaments consisting of the actin-like protein MamK are associated with the magnetosome chain. Previously, the function of MamK was thought to be in positioning magnetosome organelles; this was proposed based on observations via electron microscopy still images...
August 8, 2017: MBio
María Teresa Quirós, César Hurtado-Rodrigo, María Paz Muñoz
An unprecedented Pt-catalysed cyclisation of N-tethered 1,5-bisallenes in the presence of oxygen nucleophiles is reported, where formation of 6- or 7-membered rings is driven by the choice of nucleophile and the mechanism dictated by the nucleophile and the electronic properties of the bisallene. The reaction in the presence of alcohols gives preferentially vinyltetrahydropyridines with an extra alkoxy group and Pt-H as the active species in the catalytic cycle, while formation of di- and tetrahydroazepines with an extra hydroxyl group is favoured when water is used as nucleophile, via nucleophilic attack/carbocyclization as the favoured pathway...
August 16, 2017: Organic & Biomolecular Chemistry
Caroline C Ahrens, Ziye Dong, Wei Li
Ex vivo cell aggregates must overcome significant limitations in the transport of nutrients, drugs, and signaling proteins compared to vascularized native tissue. Further, engineered extracellular environments often fail to sufficiently replicate tethered signaling cues and the complex architecture of native tissue. Co-cultures of cells with microparticles (MPs) is a growing field directed towards overcoming many of these challenges by providing local and controlled presentation of both soluble and tethered proteins and small molecules...
August 4, 2017: Acta Biomaterialia
Juanita Garces, Mansour Mathkour, Tyler Scullen, Lora Kahn, Erin Biro, Olawale A R Sulaiman, Roger Smith, Cuong J Bui
BACKGROUND: Spinal cord transection is a radical but effective treatment for highly selective cases of symptomatic spinal re-tethering in paraplegic spina bifida patients. Autonomic dysreflexia (AD) is a potentially life-threatening syndrome involving a dysregulated sympathetic discharge reflex commonly seen following cervical and high thoracic spinal cord injury leading to a disconnect between autonomic pathways above and below the lesion that can lead to severe complications including uncontrolled hypertension, bradycardia, stroke, and potentially death...
August 3, 2017: World Neurosurgery
Miguel A Ruiz, Belén Alvarez, M Angeles Alvarez, M Esther García, Daniel Garcia Vivo
Reaction of [Mo2Cp2(μ-κ1:κ1,η6-PMes*)(CO)2] with S or Se followed by protonation with [H(OEt2)2](BAr´4) gave the cationic derivatives [Mo2Cp2{μ-κ2P,E:κ1P,η5-EP(C6H3tBu3)}(CNR)(CO)2](BAr´4) (E = S; R = tBu, iPr, Ph, 4-C6H4OMe, Xyl. E = Se; R = tBu. Ar´= 3,5-C6H3(CF3)2). Reaction of the latter with K[BHsBu3] yielded the aldimine complexes [Mo2Cp2{μ-κ2P,E:κ2P,N,η4-SP(C6H3tBu3(CHNR))}(CO)2] and their aminocarbene isomers [Mo2Cp2{μ-κ2P,E:κ2P,C,η4-SP(C6H3tBu3(NRCH))}(CO)2] (R ≠ Xyl), following respectively from C-C and C-N couplings...
August 4, 2017: Chemistry: a European Journal
Marvin Parasram, Vladimir Gevorgyan
Selective and efficient functionalization of ubiquitous C-H bonds is the Holy Grail of organic synthesis. Most advances in this area rely on employment of strongly or weakly coordinating directing groups (DGs) which have proven effective for transition-metal-catalyzed functionalization of C(sp(2))-H and C(sp(3))-H bonds. Although most directing groups are important functionalities in their own right, in certain cases, the DGs become static entities that possess very little synthetic leverage. Moreover, some of the DGs employed are cumbersome or unpractical to remove, which precludes the use of this approach in synthesis...
August 3, 2017: Accounts of Chemical Research
Jaeyeon Bae, Kangkyun Baek, Daqiang Yuan, Wooram Kim, Kimoon Kim, Hong-Cai Zhou, Jinhee Park
We report a new approach for photoinduced reduction of Cu(2+) that will enrich the structural diversity of coordination complexes and be a valuable contributor to the development of Cu(+)/Cu(0)-based catalysts. To realize controlled Cu(2+) reduction, coumarin as a triplet quencher of excited benzophenone was tethered to Cu(ii)-metal-organic polyhedra (MOPs). The photoinduced catalytic activity of the coumarin-MOPs was also examined in a Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC).
August 2, 2017: Chemical Communications: Chem Comm
Caroline Kampmeyer, Antonina Karakostova, Signe M Schenstrøm, Amanda B Abildgaard, Anne-Marie Lauridsen, Isabelle Jourdain, Rasmus Hartmann-Petersen
Exocytosis involves fusion of secretory vesicles with the plasma membrane, thereby delivering membrane proteins to the cell surface and releasing material into the extracellular space. The tethering of the secretory vesicles before membrane fusion is mediated by the exocyst, an essential phylogenetically conserved octameric protein complex. Exocyst biogenesis is regulated by several processes, but the mechanisms by which the exocyst is degraded are unknown. Here, to unravel the components of the exocyst degradation pathway, we screened for extragenic suppressors of a temperature-sensitive fission yeast strain mutated in the exocyst subunit Sec3 (sec3-913)...
August 1, 2017: Journal of Biological Chemistry
Goran Stjepanovic, Sulochanadevi Baskaran, Mary G Lin, James H Hurley
The class III phosphatidylinositol 3-kinase complex I (PI3KC3-C1) is required for the initiation of essentially all macroautophagic processes. PI3KC3-C1 consists of the lipid kinase catalytic subunit VPS34, the VPS15 scaffold, and the regulatory BECN1 and ATG14 subunits. The VPS34 catalytic domain and BECN1:ATG14 subcomplex do not touch, and it is unclear how allosteric signals are transmitted to VPS34. We used EM and crosslinking mass spectrometry to dissect five conformational substates of the complex, including one in which the VPS34 catalytic domain is dislodged from the complex but remains tethered by an intrinsically disordered linker...
August 3, 2017: Molecular Cell
Roshan L Shrestha, Duccio Conti, Naoka Tamura, Dominique Braun, Revathy A Ramalingam, Konstanty Cieslinski, Jonas Ries, Viji M Draviam
Human chromosomes are captured along microtubule walls (lateral attachment) and then tethered to microtubule-ends (end-on attachment) through a multi-step end-on conversion process. Upstream regulators that orchestrate this remarkable change in the plane of kinetochore-microtubule attachment in human cells are not known. By tracking kinetochore movements and using kinetochore markers specific to attachment status, we reveal a spatially defined role for Aurora-B kinase in retarding the end-on conversion process...
July 28, 2017: Nature Communications
David J K Swainsbury, Stefan Scheidelaar, Nicholas Foster, Rienk van Grondelle, J Antoinette Killian, Michael R Jones
Solubilisation of biological lipid bilayer membranes for analysis of their protein complement has traditionally been carried out using detergents, but there is increasing interest in the use of amphiphilic copolymers such as styrene maleic acid (SMA) for the solubilisation, purification and characterisation of integral membrane proteins in the form of protein/lipid nanodiscs. Here we survey the effectiveness of various commercially-available formulations of the SMA copolymer in solubilising Rhodobacter sphaeroides reaction centres (RCs) from photosynthetic membranes...
July 24, 2017: Biochimica et Biophysica Acta
Brian P Weiser, James T Stivers, Philip A Cole
Uracil DNA Glycosylase (UNG2) is the primary enzyme in humans that prevents the stable incorporation of deoxyuridine monophosphate into DNA in the form of U/A basepairs. During S-phase, UNG2 remains associated with the replication fork through its interactions with two proteins, Proliferating Cell Nuclear Antigen (PCNA) and Replication Protein A (RPA), which are critical for DNA replication and repair. In this work, we used protein semisynthesis and fluorescence anisotropy assays to explore the interactions of UNG2 with PCNA and RPA and to determine the effects of two UNG2 phosphorylation sites (Thr(6) and Tyr(8)) located within its PCNA-interacting motif (PIP-box)...
July 25, 2017: Biophysical Journal
Charles Thivolet, Guillaume Vial, Romeo Cassel, Jennifer Rieusset, Anne-Marie Madec
Type 2 diabetes develops when beta cells are not able to fulfill insulin needs. The role of the endoplasmic reticulum-mitochondria junction in coordinating the functions of these two organelles throughout the natural history of type 2 diabetes is determinant and may explain the alterations of insulin biosynthesis. Our goal was to study endoplasmic reticulum and mitochondrial interactions in human beta cells from organ donors with type 2 diabetes. Pancreas samples were obtained via the network for pancreatic organ donors with diabetes (nPOD) based on disease status with 12 subjects with type 2 diabetes and 9 non-diabetic controls...
2017: PloS One
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