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  • 1
    Publication Date: 2011-03-09
    Description: Diatoms are responsible for a large fraction of CO2 export to deep seawater, a process responsible for low modern-day CO2 concentrations in surface seawater and the atmosphere. Like other photosynthetic organisms, diatoms have adapted to these low ambient concentrations by operating a CO2 concentrating mechanism (CCM) to elevate the concentration of CO2 at the site of fixation. We used mass spectrometric measurements of passive and active cellular carbon fluxes and model simulations of these fluxes to better understand the stoichiometric and energetic efficiency and the physiological architecture of the diatom CCM. The membranes of diatoms are highly permeable to CO2, resulting in a large diffusive exchange of CO2 between the cell and external milieu. An active transport of carbon from the cytoplasm into the chloroplast is the main driver of the diatom CCM. Only one-third of this carbon flux is fixed photosynthetically, and the rest is lost by CO2 diffusion back to the cytoplasm. Both the passive influx of CO2 from the external medium and the recycling of the CO2 leaking out of the chloroplast are achieved by the activity of a carbonic anhydrase enzyme combined with the maintenance of a low concentration of HCO3− in the cytoplasm. To achieve the CO2 concentration necessary to saturate carbon fixation, the CO2 is most likely concentrated within the pyrenoid, an organelle within the chloroplast where the CO2-fixating enzyme is located.
    Keywords: Inaugural Articles
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 2
    Publication Date: 2015-03-20
    Description: The spliceosome plays a fundamental role in RNA metabolism by facilitating pre-RNA splicing. To understand how this essential complex is formed, we have used protein crystallography to determine the first complete structures of the key assembler protein, SMN, and the truncated isoform, SMN7, which is found in patients with the disease spinal muscular atrophy (SMA). Comparison of the structures of SMN and SMN7 shows many similar features, including the presence of two Tudor domains, but significant differences are observed in the C-terminal domain, including 12 additional amino acid residues encoded by exon 7 in SMN compared with SMN7. Mapping of missense point mutations found in some SMA patients reveals clustering around three spatial locations, with the largest cluster found in the C-terminal domain. We propose a structural model of SMN binding with the Gemin2 protein and a heptameric Sm ring, revealing a critical assembly role of the residues 260–294, with the differences at the C-terminus of SMN7 compared with SMN likely leading to loss of small nuclear ribonucleoprotein (snRNP) assembly. The SMN complex is proposed to form a dimer driven by formation of a glycine zipper involving α helix formed by amino acid residues 263–294. These results explain how structural changes of SMN give rise to loss of SMN-mediated snRNP assembly and support the hypothesis that this loss results in atrophy of neurons in SMA.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
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  • 3
    Publication Date: 2016-01-15
    Description: Many important natural products are produced by multidomain non-ribosomal peptide synthetases (NRPSs). During synthesis, intermediates are covalently bound to integrated carrier domains and transported to neighbouring catalytic domains in an assembly line fashion. Understanding the structural basis for catalysis with non-ribosomal peptide synthetases will facilitate bioengineering to create novel products. Here we describe the structures of two different holo-non-ribosomal peptide synthetase modules, each revealing a distinct step in the catalytic cycle. One structure depicts the carrier domain cofactor bound to the peptide bond-forming condensation domain, whereas a second structure captures the installation of the amino acid onto the cofactor within the adenylation domain. These structures demonstrate that a conformational change within the adenylation domain guides transfer of intermediates between domains. Furthermore, one structure shows that the condensation and adenylation domains simultaneously adopt their catalytic conformations, increasing the overall efficiency in a revised structural cycle. These structures and the single-particle electron microscopy analysis demonstrate a highly dynamic domain architecture and provide the foundation for understanding the structural mechanisms that could enable engineering of novel non-ribosomal peptide synthetases.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Drake, Eric J -- Miller, Bradley R -- Shi, Ce -- Tarrasch, Jeffrey T -- Sundlov, Jesse A -- Allen, C Leigh -- Skiniotis, Georgios -- Aldrich, Courtney C -- Gulick, Andrew M -- GM-068440/GM/NIGMS NIH HHS/ -- GM-115601/GM/NIGMS NIH HHS/ -- R01 GM068440/GM/NIGMS NIH HHS/ -- England -- Nature. 2016 Jan 14;529(7585):235-8. doi: 10.1038/nature16163.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Hauptman-Woodward Medical Research Institute, 700 Ellicott Street, Buffalo, New York 14203, USA. ; Department of Structural Biology, University at Buffalo, Buffalo, New York 14203, USA. ; Center for Drug Design and Department of Medicinal Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA. ; Life Sciences Institute and Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26762461" target="_blank"〉PubMed〈/a〉
    Keywords: Acinetobacter baumannii/*enzymology ; Biocatalysis ; Carrier Proteins/metabolism ; Coenzymes/metabolism ; Crystallography, X-Ray ; Escherichia coli/*enzymology ; Holoenzymes/*chemistry/metabolism ; Models, Molecular ; Pantetheine/analogs & derivatives/metabolism ; Peptide Synthases/*chemistry/metabolism ; Protein Structure, Tertiary
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 174 (1997), S. 359-366 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Imaging spectroscopic data of the Sii 1082.7 nm (photospheric) and Hei 1083.0 nm (chromospheric) spectral lines were taken starting 22:05 UT on 23 July, 1996 with the NASA/NSO Spectromagnetograph at the NSO/Kitt Peak Vacuum Telescope. Observations were made near the north solar pole, with a field of view of 100 by 400 arc sec and with a temporal cadence of 53 s for 2 hr. Simple fitting to the line profiles measured the line position, depth, and spectral full-width at half-maximum. Power spectra of the velocity oscillations in each line were computed, and the oscillation power in the 2 to 6 mHz frequency band versus view angle was measured to search for horizontal oscillations. Horizontal waves are not detected to limiting amplitudes (1σ) of 22 m s-1 in the chromosphere and 9 m s-1 in the photosphere. These values are used to estimate limits for the energy flux into the corona. The amplitude of radial oscillations in the chromosphere is twice that of the photosphere. No statistically meaningful oscillation power is measured in the spectral parameters of the Hei line in the emission shell seen above the continuum limb. Finally, rapidly evolving red-shift events are observed in the Hei 1083 nm line on the disk; these events are some sort of coronal rain, and there are about 40 of these events on the solar disk at any moment.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2003-10-01
    Print ISSN: 0261-4189
    Electronic ISSN: 1460-2075
    Topics: Biology , Medicine
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  • 6
    Publication Date: 2019-06-28
    Description: In the early stages of spacecraft conceptual design, an investigation of subsystem requirements and their impacts on the total system provides insight into many aspects of the spacecraft design. Such an analysis has been performed on the dual keel space station to examine the system effects contributed by three international payloads provided by the Canadian, Japanese, and European Space Agencies. This example is used to illustrate some capabilities of available computer-driven tools and methods for a system analysis. Two space station configurations were examined, one without international payloads (the baseline configuration for the study) and one with the three international payloads. Each configuration was evaluated to define viewing limitations, rigid body dynamics and controls, structural dynamics, orbit lifetime, environmental control and life support, and thermal management effects. The performance, based on each subsystem evaluation, was then compared for the two configurations, and the results and recommendations are presented.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 86-1226
    Format: text
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  • 7
    Publication Date: 2019-08-28
    Description: Megatransport objectives and constraints are briefly reviewed, and certain solutions developed by student design teams at Perdue University are summarized. Particular attention is given to the market needs and the economic risks involved in such a project; and the different approaches taken to solve the problem and difficulties faced by the design teams. A long range megatransport aircraft is aimed at carrying more than 600 passengers at reduced cost, and at the same time, reducing airport and airway congestion. The design effort must take into account airport terminal facilities; passenger loading and unloading; and defeating the 'square-cube' law to design large structures.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 93-1109 , ; 12 p.|AIAA, AHS, and ASEE, Aerospace Design Conference; Feb 16, 1993 - Feb 19, 1993; Irvine, CA; United States
    Format: text
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  • 8
    Publication Date: 2019-07-13
    Description: The Core Driven Fan Stage (CDFS) Variable Cycle Engine (VCE) has been identified as a leading candidate for advanced supersonic cruise aircraft. A scale demonstrator version of this engine has been designed and tested. This testbed engine features a split fan with double bypass capability, variable forward and aft mixers, and a variable area low pressure turbine nozzle to permit exploration and optimization of the cycle in both single and double bypass modes. This paper presents the aerodynamic performance characteristics and experimental results obtained from both the core engine and full engine tests.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AIAA PAPER 81-1594 , Joint Propulsion Conference; Jul 27, 1981 - Jul 29, 1981; Colorado Springs, CO; US
    Format: text
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