Palmitoylation Affects the Interaction of Animal Toxins with Sodium Channels

PRISMS 2009 Flow Diagram. Flow chart of data extraction process. (DOC 64 kb

Applications of the novel bio-derived solvent Cyrene™ in polymer chemistry

Polar aprotic solvents such as N-methyl-2-pyrrolidone, N,N’-dimethylformamide and N,N’-dimethylacetamide are under regulatory pressure worldwide due to their toxicity. Cyrene™, a bio-based solvent first developed by the University of York in collaboration with Circa Group made from cellulosic biomass, represents a promising alternative to polar aprotic solvents with chronic toxicity or other health-related concerns. This thesis explores the use of Cyrene as polar aprotic solvents replacement in polymer dissolution for graffiti removal, extractions of flavonoids, dispersion of carbon nanotubes, polymerisation and/or production of poly(amide-imide) wire enamels and production of filtration membranes. Cyrene proved a good cleaning agent for acrylic and cellulose-based graffiti aerosols, giving comparable results to N-methyl-2-pyrrolidone, without the latter’s chronic toxicity and chemical contamination concerns. Poly(amide-imide) enamels synthesised with Cyrene were chemical resistant, showed superior adhesion strength and were flexible. Cyrene showed up to ten times better extraction capacity of flavonoids (hesperidin and rutin) when mixed with water than using established ethanol-water mixtures and an increase to 91% when heated up to 65 °C. Cyrene demonstrated an efficient liquid media to disperse carbon nanotubes and reached concentrations up to 0.27 mg mL-1, which were stable for up to six months. Cyrene produced membranes tailored for applications from reverse osmosis (˂0.001 µm pore size) to microfiltration (0.1-10 µm) by changing polymers employed and the viscosity of the casting solution. Cyrene-based membranes showed higher porosity than usual and formed pores without the use of additives. Hansen Solubility Parameters were employed in this work to predict polymer dissolutions and discover new viable blends of Cyrene with other green solvents for these applications. This study has demonstrated the applicability of Cyrene across a broad range of applications involving polymer synthesis and fabrication of advanced materials, especially those which do not require rapid evaporation of the solvent or where higher viscosity is essential

Adsorption of small polarisable molecules using mesoporous carbonaceous materials

Discovered and first reported 11 years ago by the York Green Chemistry Centre of Excellence, Starbon® is carbonaceous mesoporous material derived from polysaccharides (starch or alginic acid). These renewable materials represent a greener, more efficient, cheaper and more selective alternative than other commercial options in reducing emissions from power stations, chemical and other large scale manufacturing plants. It has been shown that the Starbon® materials were successfully applied in chromatography, noble metals and large dye molecules adsorption. The next ambition is to utilize the unique textural properties and surface chemistry of the Starbon® for adsorption adsorption of small gas molecule. It is an interesting challenge because the microporosity is the key factor in small molecules adsorption and there is a little information about role of mesoporosity in this process. Starbons® have much lower microporosities, but adsorb up to 65% more CO2 than activated carbon. Furthermore, novel Starbons®-graphene composite materials developed during the project adsorb even more CO2 due to their very microporous combination with graphene. During the project it has been demonstrated that the adsorption capacity of the micropore system to adsorb small molecules could be significantly increased in the presence of mesopore. This phenomenon has been shown on the example of adsorption of small polarizable molecules such as CO2 and NH3. It has been found that carbonaceous materials could adsorb ammonia by micropores (reversible process) and chemically interact with their surface functional groups (irreversible process). The chemisorption of ammonia onto the Starbon® being correlated with the functionality surface and the temperature of the adsorption. Moreover, the NH3 interaction with Starbons® led to new bio-based nitrile-containing mesoporous materials. The introduction of nitrogen is expected to improve CO2 capture performance, heavy-metal binding, conductivity and catalytic activity, most notably in the metal-free oxidative reduction reaction. Because Starbons® display a high adsorption of CO2 and NH3 there may be potential to use them in the adsorption of other small molecules, as NOx, SOx. Further research would need to take place in order to discover Starbon® potential in adsorption of these small molecules

Fast-activating voltage- and calcium-dependent potassium (BK) conductance promotes bursting in pituitary cells: a dynamic clamp study.

This is the final version of the article. Available from the Society for Neuroscience via the DOI in this record.The electrical activity pattern of endocrine pituitary cells regulates their basal secretion level. Rat somatotrophs and lactotrophs exhibit spontaneous bursting and have high basal levels of hormone secretion, while gonadotrophs exhibit spontaneous spiking and have low basal hormone secretion. It has been proposed that the difference in electrical activity between bursting somatotrophs and spiking gonadotrophs is due to the presence of large conductance potassium (BK) channels on somatotrophs but not on gonadotrophs. This is one example where the role of an ion channel type may be clearly established. We demonstrate here that BK channels indeed promote bursting activity in pituitary cells. Blocking BK channels in bursting lacto-somatotroph GH4C1 cells changes their firing activity to spiking, while further adding an artificial BK conductance via dynamic clamp restores bursting. Importantly, this burst-promoting effect requires a relatively fast BK activation/deactivation, as predicted by computational models. We also show that adding a fast-activating BK conductance to spiking gonadotrophs converts the activity of these cells to bursting. Together, our results suggest that differences in BK channel expression may underlie the differences in electrical activity and basal hormone secretion levels among pituitary cell types and that the rapid rate of BK channel activation is key to its role in burst promotion.This work was supported by NIH Grant DK43200 and National Science Foundation Grant DMS0917664

Dwell time symmetry in random walks and molecular motors

The statistics of steps and dwell times in reversible molecular motors differ from those of cycle completion in enzyme kinetics. The reason is that a step is only one of several transitions in the mechanochemical cycle. As a result, theoretical results for cycle completion in enzyme kinetics do not apply to stepping data. To allow correct parameter estimation, and to guide data analysis and experiment design, a theoretical treatment is needed that takes this observation into account. In this paper, we model the distribution of dwell times and number of forward and backward steps using first passage processes, based on the assumption that forward and backward steps correspond to different directions of the same transition. We extend recent results for systems with a single cycle and consider the full dwell time distributions as well as models with multiple pathways, detectable substeps, and detachments. Our main results are a symmetry relation for the dwell time distributions in reversible motors, and a relation between certain relative step frequencies and the free energy per cycle. We demonstrate our results by analyzing recent stepping data for a bacterial flagellar motor, and discuss the implications for the efficiency and reversibility of the force-generating subunits. Key words: motor proteins; single molecule kinetics; enzyme kinetics; flagellar motor; Markov process; non-equilibrium fluctuations.Comment: revtex, 15 pages, 8 figures, 2 tables. v2: Minor revision, corrected typos, added references, and moved mathematical parts to new appendice

Enhancement of cargo processivity by cooperating molecular motors

Cellular cargo can be bound to cytoskeletal filaments by one or multiple active or passive molecular motors. Recent experiments have shown that the presence of auxiliary, nondriving motors, results in an enhanced processivity of the cargo, compared to the case of a single active motor alone. We model the observed cooperative transport process using a stochastic model that describes the dynamics of two molecular motors, an active one that moves cargo unidirectionally along a filament track and a passive one that acts as a tether. Analytical expressions obtained from our analysis are fit to experimental data to estimate the microscopic kinetic parameters of our model. Our analysis reveals two qualitatively distinct processivity-enhancing mechanisms: the passive tether can decrease the typical detachment rate of the active motor from the filament track or it can increase the corresponding reattachment rate. Our estimates unambiguously show that in the case of microtubular transport, a higher average run length arises mainly from the ability of the passive motor to keep the cargo close to the filament, enhancing the reattachment rate of an active kinesin motor that has recently detached. Instead, for myosin-driven transport along actin, the passive motor tightly tethers the cargo to the filament, suppressing the detachment rate of the active myosin.Comment: 11 pages, 8 figures, submitted to PCC

From foe to friend: using animal toxins to investigate ion channel function

Ion channels are vital contributors to cellular communication in a wide range of organisms, a distinct feature that renders this ubiquitous family of membrane-spanning proteins a prime target for toxins found in animal venom. For many years, the unique properties of these naturally-occurring molecules have enabled researchers to probe the structural and functional features of ion channels and to define their physiological roles in normal and diseased tissues. To illustrate their considerable impact on the ion channel field, this review will highlight fundamental insights into toxin-channel interactions as well as recently developed toxin screening methods and practical applications of engineered toxins