86 research outputs found
Secretory vesicle transport velocity in living cells depends on the myosin-V lever arm length
Myosins are molecular motors that exert force against actin filaments. One widely conserved myosin class, the myosin-Vs, recruits organelles to polarized sites in animal and fungal cells. However, it has been unclear whether myosin-Vs actively transport organelles, and whether the recently challenged lever arm model developed for muscle myosin applies to myosin-Vs. Here we demonstrate in living, intact yeast that secretory vesicles move rapidly toward their site of exocytosis. The maximal speed varies linearly over a wide range of lever arm lengths genetically engineered into the myosin-V heavy chain encoded by the MYO2 gene. Thus, secretory vesicle polarization is achieved through active transport by a myosin-V, and the motor mechanism is consistent with the lever arm model
Multimodel Evaluation of Nitrous Oxide Emissions From an Intensively Managed Grassland
Processâbased models are useful for assessing the impact of changing management practices and climate on yields and greenhouse gas (GHG) emissions from agricultural systems such as grasslands. They can be used to construct national GHG inventories using a Tier 3 approach. However, accurate simulations of nitrous oxide (NO) fluxes remain challenging. Models are limited by our understanding of soilâplantâmicrobe interactions and the impact of uncertainty in measured input parameters on simulated outputs. To improve model performance, thorough evaluations against in situ measurements are needed. Experimental data of NO emissions under two management practices (control with typical fertilization versus increased clover and no fertilization) were acquired in a Swiss field experiment. We conducted a multimodel evaluation with three commonly used biogeochemical models (DayCent in two variants, PaSim, APSIM in two variants) comparing four years of data. DayCent was the most accurate model for simulating NO fluxes on annual timescales, while APSIM was most accurate for daily NO fluxes. The multimodel ensemble average reduced the error in estimated annual fluxes by 41% compared to an estimate using the Intergovernmental Panel on Climate Change (IPCC)âderived method for the Swiss agricultural GHG inventory (IPCCâSwiss), but individual models were not systematically more accurate than IPCCâSwiss. The model ensemble overestimated the NO mitigation effect of the cloverâbased treatment (measured: 39â45%; ensemble: 52â57%) but was more accurate than IPCCâSwiss (IPCCâSwiss: 72â81%). These results suggest that multimodel ensembles are valuable for estimating the impact of climate and management on NO emissions
Identification of biomolecule mass transport and binding rate parameters in living cells by inverse modeling
BACKGROUND: Quantification of in-vivo biomolecule mass transport and reaction rate parameters from experimental data obtained by Fluorescence Recovery after Photobleaching (FRAP) is becoming more important. METHODS AND RESULTS: The Osborne-Moré extended version of the Levenberg-Marquardt optimization algorithm was coupled with the experimental data obtained by the Fluorescence Recovery after Photobleaching (FRAP) protocol, and the numerical solution of a set of two partial differential equations governing macromolecule mass transport and reaction in living cells, to inversely estimate optimized values of the molecular diffusion coefficient and binding rate parameters of GFP-tagged glucocorticoid receptor. The results indicate that the FRAP protocol provides enough information to estimate one parameter uniquely using a nonlinear optimization technique. Coupling FRAP experimental data with the inverse modeling strategy, one can also uniquely estimate the individual values of the binding rate coefficients if the molecular diffusion coefficient is known. One can also simultaneously estimate the dissociation rate parameter and molecular diffusion coefficient given the pseudo-association rate parameter is known. However, the protocol provides insufficient information for unique simultaneous estimation of three parameters (diffusion coefficient and binding rate parameters) owing to the high intercorrelation between the molecular diffusion coefficient and pseudo-association rate parameter. Attempts to estimate macromolecule mass transport and binding rate parameters simultaneously from FRAP data result in misleading conclusions regarding concentrations of free macromolecule and bound complex inside the cell, average binding time per vacant site, average time for diffusion of macromolecules from one site to the next, and slow or rapid mobility of biomolecules in cells. CONCLUSION: To obtain unique values for molecular diffusion coefficient and binding rate parameters from FRAP data, we propose conducting two FRAP experiments on the same class of macromolecule and cell. One experiment should be used to measure the molecular diffusion coefficient independently of binding in an effective diffusion regime and the other should be conducted in a reaction dominant or reaction-diffusion regime to quantify binding rate parameters. The method described in this paper is likely to be widely used to estimate in-vivo biomolecule mass transport and binding rate parameters
Seasonality in malaria transmission: implications for case-management with long-acting artemisinin combination therapy in sub-Saharan Africa
Fluid-mobile elements in serpentinites: Constraints on serpentinisation environments and element cycling in subduction zones
Fluid-mobile element (FME) systematics in serpentinites are key to unravel the environments of mantle rock
hydration, dehydration, and element recycling in subduction zones. Here we compile serpentinite geochemical
data and, for the first time, report discriminative FME enrichment trends for mid ocean ridge vs. forearc serpentinisation
by applying alkali element-U ratios. Characteristic element fractionations are thereby governed by
redox-dependent differential U mobility at mid ocean ridges and in forearcs, and by high Cs input in forearcs due
to fluids equilibrated with sediments. Simple modelling reproduces the observed enrichment trends in serpentinites
that range over several orders of magnitude. From these systematics, first constraints on potentially
discriminative fractionation trends for unconventional fluid tracers such as B, As, and Sb can be deduced.
Prominent W enrichments that correlate with FMEs suggest significant W mobility in low-temperature serpentinising
environments.
Application of the alkali element-U systematics to the subducted metaperidotites of Erro Tobbio (recording
initial brucite +antigorite breakdown during subduction) and Almirez (recording final antigorite breakdown)
reveal that pre-subduction FME enrichment signatures are retained in progressively subducted hydrous mantle
rocks to beyond subarc levels. Associated dehydration veins and fluid inclusions reveal subordinate alkali element-
U fractionation trends during dehydration. Subducted hydrous mantle rocks therefore may introduce
characteristic element signatures and thus contribute towards mantle geochemical heterogeneities
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