BiP-mediated closing of the Sec61 channel limits Ca(2+) leakage from the ER

In mammalian cells, signal peptide-dependent protein transport into the endoplasmic reticulum (ER) is mediated by a dynamic protein-conducting channel, the Sec61 complex. Previous work has characterized the Sec61 channel as a potential ER Ca(2+) leak channel and identified calmodulin as limiting Ca(2+) leakage in a Ca(2+)-dependent manner by binding to an IQ motif in the cytosolic aminoterminus of Sec61α. Here, we manipulated the concentration of the ER lumenal chaperone BiP in cells in different ways and used live cell Ca(2+) imaging to monitor the effects of reduced levels of BiP on ER Ca(2+) leakage. Regardless of how the BiP concentration was lowered, the absence of available BiP led to increased Ca(2+) leakage via the Sec61 complex. When we replaced wild-type Sec61α with mutant Sec61αY344H in the same model cell, however, Ca(2+) leakage from the ER increased and was no longer affected by manipulation of the BiP concentration. Thus, BiP limits ER Ca(2+) leakage through the Sec61 complex by binding to the ER lumenal loop 7 of Sec61α in the vicinity of tyrosine 344.     

Electrochemical biofilm control: mechanism of action

Although it has been previously demonstrated that an electrical current can be used to control biofilm growth on metal surfaces, the literature results are conflicting and there is no accepted mechanism of action. One of the suggested mechanisms is the production of hydrogen peroxide (H(2)O(2)) on metal surfaces. However, there are literature studies in which H(2)O(2) could not be detected in the bulk solution. This is most likely because H(2)O(2) was produced at a low concentration near the surface and could not be detected in the bulk solution. The goals of this research were (1) to develop a well-controlled system to explain the mechanism of action of the bioelectrochemical effect on 316L stainless steel (SS) surfaces and (2) to test whether the produced H(2)O(2) can reduce cell growth on metal surfaces. It was found that H(2)O(2) was produced near 316L SS surfaces when a negative potential was applied. The H(2)O(2) concentration increased towards the surface, while the dissolved oxygen decreased when the SS surface was polarized to?-600 mV(Ag/AgCl). When polarized and non-polarized surfaces with identical Pseudomonas aeruginosa PAO1 biofilms were continuously fed with air-saturated growth medium, the polarized surfaces showed minimal biofilm growth while there was significant biofilm growth on the non-polarized surfaces. Although there was no detectable H(2)O(2) in the bulk solution, it was found that the surface concentration of H(2)O(2) was able to prevent biofilm growth.     

Fatigue resistance of acrylic resin denture base material reinforced with E-glass fibres

doi: 10.1111/j.1741‐2358.2011.00548.x
Fatigue resistance of acrylic resin denture base material reinforced with E‐glass fibres Objective: The purpose of the study was to determine the effect of different forms and concentrations (2.5, 3, 4, 5% by volume) of glass fibres (chopped strand mat, continuous and woven) on fatigue resistance of acrylic denture base resin. Material and Methods: The fatigue resistance was measured by applying repeated three‐point bending deflection to the specimens, the cycle frequency of 1.05 g and magnitude of deflection of 2.0 mm. The number of loading cycles needed to cause a fracture in the test specimen was considered the fatigue resistance of the specimen. Results: The results of this study revealed that the addition of three different glass fibre forms at all concentrations to acrylic resin did not produce a statistically significant increase in the fatigue resistance (p ≥ 0.05). This study also revealed that there were significant differences (p < 0.05) between glass fibres forms used concerning the effects on the fatigue resistance. Conclusion: This study showed that the woven glass fibres had a definite superiority over the chopped fibres and the continuous fibres in regard to the fatigue resistance of the acrylic denture base resin.     

Temporal variation in drug interaction between lithium and morphine-induced analgesia

The administration-time-dependent aspects of the drug interaction between lithium and morphine-induced analgesia were studied using the mouse hot-plate test at six different times of day, each scheduled at 4 h intervals. Lithium treatment alone, in doses of 1 to 10 mmol/kg administered intraperitoneally (i.p.) did not significantly alter test latencies compared to the corresponding clock-time in saline-injected controls. Basal pain sensitivity and morphine-induced antinociceptive activity displayed significant circadian rhythms as assessed by the hot-plate response latencies, with higher values occurring during the nocturnal activity than during the daytime rest span. Acute administration of lithium, in a dose of 3 mmol/kg, 30 min prior to morphine dosing did not influence morphine-induced analgesia compared to all the clock-time test-matched morphine groups, except the 9 HALO (Hours After Lights On) one. There was a prominent potentiation of the morphine-induced antinociception at this biological time during combined drug treatment. The latter finding demonstrates that administration-time-dependent differences in drug-drug interactions need to be considered in both experimental designs and clinical settings.     

Amperometric glucose biosensor based on gold-deposited polyvinylferrocene film on Pt electrode

The preparations and performances of the novel amperometric biosensors for glucose based on immobilized glucose oxidase (GOD) on modified Pt electrodes are described. Two types of modified electrodes for the enzyme immobilization were used in this study, polyvinylferrocene (PVF) coated Pt electrode and gold deposited PVF coated Pt electrode. A simple method for the immobilization of GOD enzyme on the modified electrodes was described. The enzyme electrodes developed in this study were called as PVF-GOD enzyme electrode and PVF-Au-GOD enzyme electrode, respectively. The amperometric responses of the enzyme electrodes were measured at constant potential, which was due to the electrooxidation of enzymatically produced H2O2. The electrocatalytic effects of the polymer, PVF, and the gold particles towards the electrooxidation of the enzymatically generated H2O2 offers sensitive and selective monitoring of glucose. The biosensor based on PVF-Au-GOD electrode has 6.6 times larger maximum current, 3.8 times higher sensitivity and 1.6 times larger linear working portion than those of the biosensor based on PVF-GOD electrode. The effects of the applied potential, the thickness of the polymeric film, the amount of the immobilized enzyme, pH, the amount of the deposited Au, temperature and substrate concentration on the responses of the biosensors were investigated. The optimum pH was found to be pH 7.4 at 25 degrees C. Finally the effects of interferents, stability of the biosensors and applicability to serum analysis of the biosensor were also investigated.     

Analysis and network representation of hotspots in protein interfaces using minimum cut trees

We propose a novel approach to analyze and visualize residue contact networks of protein interfaces by graph‐based algorithms using a minimum cut tree (mincut tree). Edges in the network are weighted according to an energy function derived from knowledge‐based potentials. The mincut tree, which is constructed from the weighted residue network, simplifies and summarizes the complex structure of the contact network by an efficient and informative representation. This representation offers a comprehensible view of critical residues and facilitates the inspection of their organization. We observed, on a nonredundant data set of 38 protein complexes with experimental hotspots that the highest degree node in the mincut tree usually corresponds to an experimental hotspot. Further, hotspots are found in a few paths in the mincut tree. In addition, we examine the organization of hotspots (hot regions) using an iterative clustering algorithm on two different case studies. We find that distinct hot regions are located on specific sites of the mincut tree and some critical residues hold these clusters together. Clustering of the interface residues provides information about the relation of hot regions with each other. Our new approach is useful at the molecular level for both identification of critical paths in the protein interfaces and extraction of hot regions by clustering of the interface residues. Proteins 2010. © 2010 Wiley‐Liss, Inc.     

Prediction of the extent of thermal damage in the cornea during conductive keratoplasty

Conductive keratoplasty (CK) is a sub-ablative thermal therapy used to treat hyperopia and presbyopia. In this study, a 3-D finite element model of the cornea was developed to predict the transient temperature distributions and the resultant thermal damage fields in the cornea during simulated CK procedures. The model incorporated collagen denaturation and vaporization of water as well as ablation-induced thermal/electrical contact loss. The effects of the radiofrequency power applied on the electrode and the duration of the treatment on the extent of thermal damage in the tissue were examined and compared with the previously published experimental results on human cornea. It was shown that with clinical settings (60% power and 0.6 s treatment duration), the temperature maximum near the tip of the radiofrequency probe exceeded the temperature for vaporization. The results also indicated that the increase in the treatment duration had a much more significant effect on the size of the thermally modified region than increased radiofrequency power (as verified by the experimental results). The model predictions matched the experimental results well and showed the feasibility of using simulations to optimize thermal treatment of the cornea.