Ion Selectivity and Allostery in the NaK Channel

Ion channels require proper ion selectivity and regulated gating in order to perform their cellular functions. Bacterial ion channels serve as excellent model systems to study structure/function relationships concerning the fundamental processes of ion selectivity and gating. NaK, a non-selective cation channel from Bacillus cereus, has the conserved pore structure of K+ channels. However, its non-canonical selectivity filter structure leads to non-selectivity between Na+ and K+. Full selectivity is restored with two mutations that lead to the restoration of a Kcsa-like selectivity filter structure. Many mutations can be made to the selectivity filter of NaK without loss of protein stability or function, and this structural stability makes it an excellent model system to study the molecular mechanism of ion selectivity. Experimental measurements on the dynamics and stability of the selectivity filter and how this relates to ion selective have not been performed in this system. The data presented in this thesis establishes that solution NMR dynamic studies of NaK that will lead to a better understanding of how backbone dynamics tune ion selectivity. The results presented here also reveal an unexpected allostery between the selectivity filter and inner gate of NaK. Allosteric coupling between the selectivity filter and inner gate links gating at the selectivity filter (C-type inactivation) to the state of the inner gate, thus regulating the cycle of channel gating. My work demonstrates that this coupling is an intrinsic structural and dynamic property of NaK and is mechanistically distinct from the well-studied KcsA model. Allostery in channel gating is also important for transmitting signals from regulatory domains to the channel pore. I investigated this coupling of the amphipathic regulatory helix of NaK to the inner gate and found that interaction is mediated through inter- and intra-molecular side chain interactions between M0 and the pore domain. When these interactions are disrupted, the channel reverts to a state similar to what is seen without the regulatory helix

Microchannel heat transfer with slip flow and wall effects

Cataloged from PDF version of article.Analysis is presented for conjugate heat transfer in a parallel-plate microchannel. Axial conduction in the fluid and in the adjacent wall is included. The fluid is a constant property gas with a slip-flow velocity distribution. The microchannel is heated by a small region on the channel wall. The analytic solution is given in the form of integrals by the method of Green's functions. Quadrature is used to obtain numerical results for the temperature and heat transfer coefficient on the heated region for various Peclet number, Knudsen number, and wall materials. A region downstream of the heater is also explored. These results have application in the optimal design of small-scale heat transfer devices for biomedical applications, electronic cooling, and advanced fuel cells

Effect of Superplasticizers on Concrete-Steel Bond Strength

The effects of superp 1 asti ci zers on concrete-steel bond strength are studied. Key variables are degree of consolidation, concrete slump, both with and without a superplasticizer, concrete temperature, and bar position. #8 deformed reinforcing bars were used with a 2 in. cover and a 10 in. bonded length. Concrete slumps ranged from 1-3/4 in. to 9 in. Three specimen depths were used. All specimens were modified cantilever beam specimens. Based on the experimental results, high slump superplasticized concrete pro vi des a 1 ower bond strength than 1 ow slump concrete of the same strength. Superpl asti ci zed concrete pro vi des a higher bond strength than high slump regular concrete with the same slump and water-cement ratio. Vibration of high slump concrete increases the bond strength compared to high slump concrete without vibration. Bond strength decreases as the amount of concrete below a bar increases, but the greatest effect appears to occur with top-cast (i.e. upper surface) bars

Conformational plasticity of NaK2K and TREK2 potassium channel selectivity filters

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Amorphous formulations of indomethacin and griseofulvin prepared by electrospinning

Following an array of optimization experiments, two series of electrospun polyvinylpyrrolidone (PVP) fibers were prepared. One set of fibers contained various loadings of indomethacin, known to form stable glasses, and the other griseofulvin (a poor glass former). Drug loadings of up to 33% w/w were achieved. Electron microscopy data showed the fibers largely to comprise smooth and uniform cylinders, with evidence for solvent droplets in some samples. In all cases, the drug was found to exist in the amorphous physical state in the fibers on the basis of X-ray diffraction and differential scanning calorimetry (DSC) measurements. Modulated temperature DSC showed that the relationship between a formulation’s glass transition temperature (<i>T</i>_g) and the drug loading follows the Gordon–Taylor equation, but not the Fox equation. The results of Gordon–Taylor analysis indicated that the drug/polymer interactions were stronger with indomethacin. The interactions between drug and polymer were explored in more detail using molecular modeling simulations and again found to be stronger with indomethacin; the presence of significant intermolecular forces was further confirmed using IR spectroscopy. The amorphous form of both drugs was found to be stable after storage of the fibers for 8 months in a desiccator (relative humidity <25%). Finally, the functional performance of the fibers was studied; in all cases, the drug-loaded fibers released their drug cargo very rapidly, offering accelerated dissolution over the pure drug

Microchannel heat transfer with slip flow and wall effects

Analysis is presented for conjugate heat transfer in a parallel-plate microchannel. Axial conduction in the fluid and in the adjacent wall is included. The fluid is a constant property gas with a slip-flow velocity distribution. The microchannel is heated by a small region on the channel wall. The analytic solution is given in the form of integrals by the method of Green's functions. Quadrature is used to obtain numerical results for the temperature and heat transfer coefficient on the heated region for various Peclet number, Knudsen number, and wall materials. A region downstream of the heater is also explored. These results have application in the optimal design of small-scale heat transfer devices for biomedical applications, electronic cooling, and advanced fuel cells. © 2014 by the American Institute of Aeronautics and Astronautics, Inc

Bond of Reinforcement to Superplasticized Concrete

The effects of superplasticizers on concrete-steel bond strength were studied. Key variables were degree of consolidation; concrete slump, both with and without a superplasticizer; concrete temperature; and bar position. No. 8 deformed reinforcing bars were used with a 2-in (51mm) cover and a 10 in. (254 mm) bonded length. Concrete slumps ranged from 1 3/4 in to 9in. (44 to 229 mm). Three specimens depths were used. All specimens were modified cantilever beam specimens. The experimental results show that high-slump superplasticized concrete provides a lower bond strength than low-slump concrete of the same strength. Vibration of high-slump concrete increases the bond strength compared to high-slump concrete without vibration. The current ACI top-bar requirements appear to be unconservative for top-cast bars with less than 12 in. (305 mm) of concrete below the bar and are possibly overconservative for nontop-cast bars with more than 12 in. 305 (mm) of concrete below the bar when low-slump concrete is used