A Genetic Screen for Dihydropyridine (DHP)-Resistant Worms Reveals New Residues Required for DHP-Blockage of Mammalian Calcium Channels

Dihydropyridines (DHPs) are L-type calcium channel (Cav1) blockers prescribed to treat several diseases including hypertension. Cav1 channels normally exist in three states: a resting closed state, an open state that is triggered by membrane depolarization, followed by a non-conducting inactivated state that is triggered by the influx of calcium ions, and a rapid change in voltage. DHP binding is thought to alter the conformation of the channel, possibly by engaging a mechanism similar to voltage dependent inactivation, and locking a calcium ion in the pore, thereby blocking channel conductance. As a Cav1 channel crystal structure is lacking, the current model of DHP action has largely been achieved by investigating the role of candidate Cav1 residues in mediating DHP-sensitivity. To better understand DHP-block and identify additional Cav1 residues important for DHP-sensitivity, we screened 440,000 randomly mutated Caenorhabditis elegans genomes for worms resistant to DHP-induced growth defects. We identified 30 missense mutations in the worm Cav1 pore-forming (α1) subunit, including eleven in conserved residues known to be necessary for DHP-binding. The remaining polymorphisms are in eight conserved residues not previously associated with DHP-sensitivity. Intriguingly, all of the worm mutants that we analyzed phenotypically exhibited increased channel activity. We also created orthologous mutations in the rat α1C subunit and examined the DHP-block of current through the mutant channels in culture. Six of the seven mutant channels examined either decreased the DHP-sensitivity of the channel and/or exhibited significant residual current at DHP concentrations sufficient to block wild-type channels. Our results further support the idea that DHP-block is intimately associated with voltage dependent inactivation and underscores the utility of C. elegans as a screening tool to identify residues important for DHP interaction with mammalian Cav1 channels

A pH Dependant Switch in DHP Oxidation Mechanism

Dehaloperoxidase (DHP) is a multifunctional enzyme found in Amphitrite ornata, a sediment-dwelling marine worm. This enzyme possess the structure of a traditional hemoglobin enzyme and serves as the primary oxygen carrier in A. ornata; however, it also possesses peroxidase and peroxygenase capabilities. These secondary oxidative functions provide a remarkable ability for A. ornata to resist the effects of toxic metabolites secreted by other organisms that cohabit its benthic ecosystem. This study will analyze the novel catalytic switching between peroxygenase and peroxidase oxidation mechanisms employed by DHP in response to pH changes

Solving propeller design problems easily with the Wageningen B-series in modified Bpu-δ form

In this volume we present the new [n-DHP], [D-DHP], [n-T] and [D-T] contour plots for the Wageningen B-series for all combinations of: z=3 to 7, AE/A0=0.5 to 1.05 step 0.05, Re75%R= 2.10^6, 2.10^7, 2.10^8, 2.10^9. [n-DHP], [D-DHP], [n-T] and [D-T] contour plots are modified forms of the classical Taylors's Bpu-δ contour plots and can be used for effortless solution of marine propeller design problems. The book starts with a brief historical exposition regarding the Bpu-δ graphs and then introduces in detail the new [n-DHP], [D-DHP], [n-T] and [D-T] contour plots. A numerical example is also presented for using the contour plots. The contents of the book are as follows: 1. Historical remarks 2. Introducing the modified Taylor’s Bpu-δ contour plots 3. Naming convention for the modified Taylor’s Bpu-δ contour plots 4. [n-DHP], [D-DHP], [n-T] and [D-T] contour plots for the Wageningen B-series 5. How to use contour plots [n-DHP], [D-DHP], [n-T] and [D-T] to solve propeller design problems effortlessly 6. Some interesting correlations 7. A numerical example 8. Useful units an conversion factors 9. References 10. List of [n-DHP], [D-DHP], [n-T] and [D-T] contour plots Total number of pages: 1143 in PDF format with detailed inde

HURDLE COUNT-DATA MODELS IN RECREATION DEMAND ANALYSIS

When a sample of recreators is drawn from the general population using a survey, many in the sample will not recreate at a recreation site of interest. This study focuses on nonparticipation in recreation demand modeling and the use of modified count-data models. We clarify the meaning of the single-hurdle Poisson (SHP) model and derive the double-hurdle Poisson (DHP) model. The latter is contrasted with the SHP and we show the DHP is consistent with Johnson and Kotz's zero-modified Poisson model.Resource /Energy Economics and Policy,

A Comparison of Learning Speed and Ability to Cope Without Exploration between DHP and TD(0)

This paper demonstrates the principal motivations for Dual Heuristic Dynamic Programming (DHP) learning methods for use in Adaptive Dynamic Programming and Reinforcement Learning, in continuous state spaces: that of automatic local exploration, improved learning speed and the ability to work without stochastic exploration in deterministic environments. In a simple experiment, the learning speed of DHP is shown to be around 1700 times faster than TD(0). DHP solves the problem without any exploration, whereas TD(0) cannot solve it without explicit exploration. DHP requires knowledge of, and differentiability of, the environment's model functions. This paper aims to illustrate the advantages of DHP when these two requirements are satisfied

The Importance of Clipping in Neurocontrol by Direct Gradient Descent on the Cost-to-Go Function and in Adaptive Dynamic Programming

In adaptive dynamic programming, neurocontrol and reinforcement learning, the objective is for an agent to learn to choose actions so as to minimise a total cost function. In this paper we show that when discretized time is used to model the motion of the agent, it can be very important to do "clipping" on the motion of the agent in the final time step of the trajectory. By clipping we mean that the final time step of the trajectory is to be truncated such that the agent stops exactly at the first terminal state reached, and no distance further. We demonstrate that when clipping is omitted, learning performance can fail to reach the optimum; and when clipping is done properly, learning performance can improve significantly. The clipping problem we describe affects algorithms which use explicit derivatives of the model functions of the environment to calculate a learning gradient. These include Backpropagation Through Time for Control, and methods based on Dual Heuristic Dynamic Programming. However the clipping problem does not significantly affect methods based on Heuristic Dynamic Programming, Temporal Differences or Policy Gradient Learning algorithms. Similarly, the clipping problem does not affect fixed-length finite-horizon problems

Cyclic di-GMP mediates a histidine kinase/phosphatase switch by noncovalent domain cross-linking

Histidine kinases are key components of regulatory networks in bacteria. Although many of these enzymes are bifunctional, mediating both phosphorylation and dephosphorylation of downstream targets, the molecular details of this central regulatory switch are unclear. We showed recently that the universal second messenger cyclic di-guanosine monophosphate (c-di-GMP) drives Caulobacter crescentus cell cycle progression by forcing the cell cycle kinase CckA from its default kinase into phosphatase mode. We use a combination of structure determination, modeling, and functional analysis to demonstrate that c-di-GMP reciprocally regulates the two antagonistic CckA activities through noncovalent cross-linking of the catalytic domain with the dimerization histidine phosphotransfer (DHp) domain. We demonstrate that both c-di-GMP and ADP (adenosine diphosphate) promote phosphatase activity and propose that c-di-GMP stabilizes the ADP-bound quaternary structure, which allows the receiver domain to access the dimeric DHp stem for dephosphorylation. In silico analyses predict that c-di-GMP control is widespread among bacterial histidine kinases, arguing that it can replace or modulate canonical transmembrane signaling