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  • 1
    ISSN: 1075-2617
    Keywords: FMDV ; structure ; NMR spectrocopy ; NEO constraints ; RGD (Arg-Gly-Asp) ; Chemistry ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution structure of a 20 amino acid long peptide corresponding to the region 141-160 of the envelope protein Vp1 from foot-and-mouth disease virus (FMDV) serotype A, variant A, has been determined by a combination of NMR experiments and computer calculations. The peptide contains both the immunodominant epitope as well as the sequence (RGD) used by the virus to bind the cell receptor in the initial stages of infection. These two sites have been shown to partially overlap.One hundred and thirty-five NMR distance constraints were used to obtain a set of 11 structures by distance geometry, minimization and molecular dynamics simulations. These structures were divided into two homogeneous families based upon backbone superimposition. The first and most populated family was characterized by a backbone RMS of 1.5±0.4 Å, the second by a backbone RMS of 0.8±0.2 Å. The two families had similar structural features and differed mainly in the backbone angles of G149. In the larger of the two families these angles favoured the formation of a loop comprising residues 147 to 152 and stabilized by a H-bond between the NH of D147 and the CO of A152. In the second family, where this bond was absent, the peptide adopted in this region the shape of an irregular helix. The C-terminal half of the peptide (152-159) was similar in both families and largely helical. Similar structural features were also found within the VRGDS sequence (144-148) which was assigned to a β-turn type IV. The features of the two families of structures were found to be different from those of the recently published X-ray structure of the antigenic loop of a chemically modified form of FMDV. Proposals accounting for these differences are provided which take into account the dual activity of the 141-160 sequence (i.e. antibody binding and cell invasion through receptor binding).
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1075-2617
    Keywords: FMDV ; NMR spectrocopy ; RGD (Arg-Gly-Asp) ; NEO constraints ; structure-activity correlation ; Chemistry ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution structure of a peptide corresponding to the VP1 region 141-160 of foot-and-mouth disease virus (FMDV) serotype A variant USA has been studied by NMR and computer calculations and compared with the results from a study on a highly homologous peptide deriving from serotype A, variant A. The two peptides differ in their serological behaviour and contain the immunodominant epitope of the virus which partly overlaps with its receptor binding region. Distance constraints, derived both from 2D and 3D homonuclear NMR and 2D-heteronuclear NMR experiments, were combined with DG calculations to yield 50 structures. After refinement through EM and restrained molecular dynamics simulations the selected structures shared several general features. In particular the 151-158 region was a helix in all cases while a large loop similar to that found in peptide A but comprising less residues and stabilized by an H-bond between the side chains of D147 and S150 was found in the majority of structures. A further loop, common to all structures, was identified around the RGD sequence (145-147). This was different from that found in the corresponding region of peptide A as were the conformations of the individual residues within the RGDX sequence.The different structural features shown by the two peptides were rationalized in terms of the S148 (peptide A) to F148 (peptide USA) mutation. The second mutation, that at position 153 (L in A, P in USA) did not appear to affect the structure of the peptide significantly although the different dimensions of the loop in the central region and the type of H-bond stabilizing it could be potentially ascribed to this second mutation.All criteria used pointed to different structural features for the two peptides consistent with their serological behaviour.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2019-07-17
    Description: The Vegetation Canopy Lidar (VCL) mission, expected to launch in the spring of 2002, will carry a unique Multi-Beam Laser Altimeter (MBLA) instrument designed to observe vegetative canopy structure for a nominal mission duration of 2 years. The VCL MBLA is a three-beam instrument where each laser is capable of producing returns with 30-m along-track spacing and 25-m-diameter footprints. Identifying the precise location of the point on the Earth's surface from which the laser energy reflects is a critical issue in the validation and application of the data. The resultant geolocation accuracy is dependent on the performance of many components of the VCL system including: laser pulse round trip travel time observation to surface, navigation tracking data, attitude determination system data, timing, laser pointing and body orientation stability, knowledge of instrument and navigation tracking point positions, media and geophysical corrections. Additionally, it is critical to calibrate on-orbit instrument parameters including pointing and range corrections. The geolocation and calibration methodology and algorithms will be summarized. A detailed geolocation error analysis identifying the contributions from each system component, along with the resultant expected geolocation accuracy, will be presented. A brief discussion of the operational geolocation process will also be presented. Science and data validation implications from geolocation performance will be summarized.
    Keywords: Earth Resources and Remote Sensing
    Type: 2000 Fall Meeting; Dec 15, 2000 - Dec 19, 2000; San Francisco, CA; United States
    Format: text
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  • 4
    Publication Date: 2019-07-18
    Description: With the launch of CHAMP and GRACE, we have entered a new phase in the history of satellite geodesy. For the first time, geopotential models are now available based almost exclusively on satellite-satellite tracking either with GPS in the case of the CHAMP-based geopotential models, or co-orbital intersatellite ultra-precise ranging in the case of GRACE. Different groups have analyzed these data, and produced a series of geopotential models (e.g., EIGENlS, EIGEN2, GGM0lS, GGMOlC) that incorporate the new data. We will compare the performance of these "newer" geopotential models with the standard models now used for computations, (e.g., JGM-3, BGM-96, PGS7727, and GRIMS-C1) for TOPEX, JASON, Geosat-Follow-On (GFO), and Envisat using standard metrics such as SLR RMS of fit, altimeter crossovers, and orbit overlaps. Where covariances are available we can evaluate the predicted geographically correlated orbit error. These predicted results can be compared with the Earth-fixed differences between dynamic and reduced-dynamic orbits to test the predictive accuracy of the covariances, as well as to calibrate the error of the solutions.
    Keywords: Earth Resources and Remote Sensing
    Type: TOPEX JASON Science Working Team Meeting; Nov 18, 2003 - Nov 21, 2003; Arles; France
    Format: text
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  • 5
    Publication Date: 2019-07-13
    Description: Launched in the summer of 1992, TOPEX/POSEIDON (T/P) was a joint mission between NASA and the Centre National d Etudes Spatiales (CNES), the French Space Agency, to make precise radar altimeter measurements of the ocean surface. After the remarkably successful 13-years of mapping the ocean surface T/P lost its ability to maneuver and was de-commissioned January 2006. T/P revolutionized the study of the Earth s oceans by vastly exceeding pre-launch estimates of surface height accuracy recoverable from radar altimeter measurements. The precision orbit lies at the heart of the altimeter measurement providing the reference frame from which the radar altimeter measurements are made. The expected quality of orbit knowledge had limited the measurement accuracy expectations of past altimeter missions, and still remains a major component in the error budget of all altimeter missions. This paper describes critical improvements made to the T/P orbit time series over the 13-years of precise orbit determination (POD) provided by the GSFC Space Geodesy Laboratory. The POD improvements from the pre-launch T/P expectation of radial orbit accuracy and Mission requirement of 13-cm to an expected accuracy of about 1.5-cm with today s latest orbits will be discussed. The latest orbits with 1.5 cm RMS radial accuracy represent a significant improvement to the 2.0-cm accuracy orbits currently available on the T/P Geophysical Data Record (GDR) altimeter product.
    Keywords: Earth Resources and Remote Sensing
    Type: AIAA/AAS Astrodynamics Conference; Aug 21, 2006 - Aug 24, 2006; Keystone, CO; United States
    Format: application/pdf
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