868 research outputs found
THE DYNAMICS OF FEEDER CATTLE MARKET RESPONSES TO CORN PRICE CHANGE
No full textA feeder-calf price model is estimated which incorporates elements of break-even budget analysis, including estimates of placement weights, slaughter weights, ration cost, and feed-conversion rates. From this model, a corn price multiplier is calculated which quantifies the corn/feeder-calf price relationship. Because the multiplier includes information on cattle weight, feed conversion, and ration cost, it also provides insight into how feeding programs are altered in response to corn price changes. Changes in feeding programs which occur in response to corn price changes are illustrated with dynamic simulation based on weight, ration cost, and price models presented here.corn, corn price multiplier, dynamic simulation, feeder cattle, Demand and Price Analysis,
The Architecture of the Multisubunit TRAPP I Complex Suggests a Model for Vesicle Tethering
No full textTransport protein particle (TRAPP) I is a multisubunit vesicle tethering factor composed of seven subunits involved in ER-to-Golgi trafficking. The functional mechanism of the complex and how the subunits interact to form a functional unit are unknown. Here, we have used a multidisciplinary approach that includes X-ray crystallography, electron microscopy, biochemistry, and yeast genetics to elucidate the architecture of TRAPP I. The complex is organized through lateral juxtaposition of the subunits into a flat and elongated particle. We have also localized the site of guanine nucleotide exchange activity to a highly conserved surface encompassing several subunits. We propose that TRAPP I attaches to Golgi membranes with its large flat surface containing many highly conserved residues and forms a platform for protein-protein interactions. This study provides the most comprehensive view of a multisubunit vesicle tethering complex to date, based on which a model for the function of this complex, involving Rab1-GTP and long, coiled-coil tethers, is presentedNRC publication: Ye
Direct comparison of elastic incoherent neutron scattering experiments with molecular dynamics simulations of DMPC phase transitions
No full textNeutron scattering techniques have been employed to investigate 1,2 dimyristoyl sn glycero 3 phosphocholine DMPC membranes in the form of multilamellar vesicles MLVs and deposited, stacked multilamellar bilayers MLBs , covering transitions from the gel to the liquid phase. Neutron diffraction was used to characterise the samples in terms of transition temperatures, whereas elastic incoherent neutron scattering EINS demonstrates that the dynamics on the sub macromolecular length scale and pico to nano second time scale are correlated with the structural transitions through a discontinuity in the observed elastic intensities and the derived mean square displacements. Molecular dynamics simulations have been performed in parallel focussing on the length , time and temperature scales of the neutron experiments. They correctly reproduce the structural features of the main gel liquid phase transition. Particular emphasis is placed on the dynamical amplitudes derived from experiment and simulations. Two methods are used to analyse the experimental data and mean square displacements. They agree within a factor of 2 irrespective of the probed time scale, i.e. the instrument utilized. Mean square displacements computed from simulations show a comparable level of agreement with the experimental values, albeit, the best match with the two methods varies for the two instruments. Consequently, experiments and simulations together give a consistent picture of the structural and dynamical aspects of the main lipid transition and provide a basis for future, theoretical modelling of dynamics and phase behaviour in membranes. The need for more detailed analytical models is pointed out by the remaining variation of the dynamical amplitudes derived in two different ways from experiments on the one hand and simulations on the othe
Interactions between Transport Protein Particle (TRAPP) complexes and Rab GTPases in Arabidopsis.
No full textTransport Protein Particle II (TRAPPII) is essential for exocytosis, endocytosis, protein sorting and cytokinesis. In spite of a considerable understanding of its biological role, little information is known about Arabidopsis TRAPPII complex topology and molecular function. In this study, independent proteomic approaches initiated with TRAPP components or Rab-A GTPase variants converge on the TRAPPII complex. We show that the Arabidopsis genome encodes the full complement of 13 TRAPPC subunits, including four previously unidentified components. A dimerization model is proposed to account for binary interactions between TRAPPII subunits. Preferential binding to dominant negative (GDP-bound) versus wild-type or constitutively active (GTP-bound) RAB-A2a variants discriminates between TRAPPII and TRAPPIII subunits and shows that Arabidopsis complexes differ from yeast but resemble metazoan TRAPP complexes. Analyzes of Rab-A mutant variants in trappii backgrounds provide genetic evidence that TRAPPII functions upstream of RAB-A2a, allowing us to propose that TRAPPII is likely to behave as a guanine nucleotide exchange factor (GEF) for the RAB-A2a GTPase. GEFs catalyze exchange of GDP for GTP; the GTP-bound, activated, Rab then recruits a diverse local network of Rab effectors to specify membrane identity in subsequent vesicle fusion events. Understanding GEF-Rab interactions will be crucial to unravel the co-ordination of plant membrane traffic
Mislocalized TRAPP-II complex can ectopically target vesicles and tubulovesicular membrane structures to mitochondria.
No full text(A–D) EM images (A–C) and quantification (D) showing post-Golgi secretory vesicles (arrowheads) or elongated tubulovesicular membrane structures (yellow arrows, maybe specialized late-Golgi cisternae or recycling endosomes) mis-targeted and tethered to mitochondria (M) in cells expressing Tom20-GBP Sec3-GFP (B) or Tom20-GBP Trs120-3GFP (C) but not Tom20-GBP alone (A). Some free vesicles (asterisks) or tubulovesicular structures (red arrows) accumulated in the cytoplasm or near the active growth sites were marked. N = Nucleus, S = septum. (D) Quantification of the mitochondria associated with mis-targeted secretory vesicles or tubulovesicular structures. (E) A working model for the roles of the exocyst and TRAPP-II complexes in vesicle trafficking and membrane deposition at the cleavage furrow during cytokinesis. The events 1–6 are symmetrical at the division site and omitted at some locations for clarity. 1. New membrane is deposited throughout the cleavage furrow. 2. Endocytic vesicles are mostly generated at the rim of the division plane or the adjacent regions and may become tubulovesicular structures like recycling endosomes. 3. Myosin-Vs transport secretory vesicles or recycling endosome equivalents along actin cables to the division plane. 4. Secretory vesicles can also reach the division site by actin-independent random walk. 5. Exocyst complexes localize to the rim of the cleavage furrow and preferentially tether 90-nm secretory vesicles probably through interaction with Rab8 GTPase Ypt2. 6. TRAPP-II complexes localize along the cleavage furrow (slightly biased to the leading edge) to directly tether or indirectly promote the tethering of Rab11 GTPase Ypt3-labeled recycling endosome equivalents or 90-nm secretory vesicles.</p
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