scholarly journals Heme as an optical probe of a conformational transition of ovine recPrP

2004 ◽  
Vol 13 (4) ◽  
pp. 1100-1107 ◽  
Author(s):  
C. Pato
Keyword(s):  
Conformational Transition ◽  
Optical Probe

Water-soluble Polythiophene as an Optical Probe for Detection of the Helicity and Conformational Transition in Polysaccharides

2005 ◽  
Vol 34 (10) ◽  
pp. 1354-1355 ◽  
Author(s):  
Chun Li ◽  
Munenori Numata ◽  
Teruaki Hasegawa ◽  
Kazuo Sakurai ◽  
Seiji Shinkai
Keyword(s):  
Conformational Transition ◽  
Optical Probe ◽  
Water Soluble

Constant pH Molecular Dynamics Reveals How Proton Release Drives the Conformational Transition of a Transmembrane Efflux Pump

2017 ◽  
Author(s):  
Jana Shen ◽  
Zhi Yue ◽  
Helen Zgurskaya ◽  
Wei Chen
Keyword(s):  
Molecular Dynamics ◽  
Conformational Changes ◽  
Transmembrane Domain ◽  
Conformational Transition ◽  
Conformational Dynamics ◽  
Proton Release ◽  
Intrinsic Resistance ◽  
Constant Ph ◽  
Wide Range ◽  
Constant Ph Molecular Dynamics

AcrB is the inner-membrane transporter of E. coli AcrAB-TolC tripartite efflux complex, which plays a major role in the intrinsic resistance to clinically important antibiotics. AcrB pumps a wide range of toxic substrates by utilizing the proton gradient between periplasm and cytoplasm. Crystal structures of AcrB revealed three distinct conformational states of the transport cycle, substrate access, binding and extrusion, or loose (L), tight (T) and open (O) states. However, the specific residue(s) responsible for proton binding/release and the mechanism of proton-coupled conformational cycling remain controversial. Here we use the newly developed membrane hybrid-solvent continuous constant pH molecular dynamics technique to explore the protonation states and conformational dynamics of the transmembrane domain of AcrB. Simulations show that both Asp407 and Asp408 are deprotonated in the L/T states, while only Asp408 is protonated in the O state. Remarkably, release of a proton from Asp408 in the O state results in large conformational changes, such as the lateral and vertical movement of transmembrane helices as well as the salt-bridge formation between Asp408 and Lys940 and other sidechain rearrangements among essential residues.Consistent with the crystallographic differences between the O and L protomers, simulations offer dynamic details of how proton release drives the O-to-L transition in AcrB and address the controversy regarding the proton/drug stoichiometry. This work offers a significant step towards characterizing the complete cycle of proton-coupled drug transport in AcrB and further validates the membrane hybrid-solvent CpHMD technique for studies of proton-coupled transmembrane proteins which are currently poorly understood. <p><br></p>

Spectrocoulometry – a new spectro-electrochemical technique

1987 ◽  
Vol 52 (6) ◽  
pp. 1386-1396 ◽  
Author(s):  
Ján Mocák ◽  
Michal Németh ◽  
Mieczyslaw Lapkowski ◽  
Jerzy W. Strojek
Keyword(s):  
Optical Probe ◽  
Optical Signal ◽  
Open Circuit ◽  
Electrochemical Technique ◽  
Kinetics Of Oxidation ◽  
Hydrolytic Reaction ◽  
Experimental Errors ◽  
Mechanism And Kinetics ◽  
Kinetics Of

A spectrocoulometric macrocell with a direct-view optical probe was designed and constructed, where the optical signal is transferred by light-conducting glass or quartz fibres permitting to work at wavelengths above 410 or 300 nm. The method of measurement on the proposed equipment is described; it was tested in the study of the mechanism and kinetics of oxidation of Fe(bipy)32+ ions (bipy = 2,2'-bipyridyl) with the use of potentiostatic coulometric electrolysis with open-circuit relaxation at a suitable time. The primary product of electrolysis, Fe(bipy)33+, undergoes a follow-up hydrolytic reaction with the formation of a binuclear complex. The rate constant of the reaction of the first order involves the contributions, kBi, from all bases present in solution; the corresponding values for H2O, OH-, bipy, and CH3COO- ions at a ionic strength 0·5 mol dm-3 and 25 °C were determined as kOH = (5·0 ± 0·6) . 105 mol-1 dm3 s-1, kbipy = (1·3 ± 0·2) . 10-1 mol-1 dm3 s-1, kAc = (5·8 ± 1·0) . 10-2 mol-1 dm3 s-1, and kH2O is not significant with respect to experimental errors.

scholarly journals Stu2p binds tubulin and undergoes an open-to-closed conformational change

2006 ◽  
Vol 172 (7) ◽  
pp. 1009-1022 ◽  
Author(s):  
Jawdat Al-Bassam ◽  
Mark van Breugel ◽  
Stephen C. Harrison ◽  
Anthony Hyman
Keyword(s):  
Conformational Change ◽  
Conformational Transition ◽  
Budding Yeast ◽  
Microtubule Dynamics ◽  
Open Structure ◽  
Microtubule Associated Proteins ◽  
Associated Proteins ◽  
The Common

Stu2p from budding yeast belongs to the conserved Dis1/XMAP215 family of microtubule-associated proteins (MAPs). The common feature of proteins in this family is the presence of HEAT repeat–containing TOG domains near the NH2 terminus. We have investigated the functions of the two TOG domains of Stu2p in vivo and in vitro. Our data suggest that Stu2p regulates microtubule dynamics through two separate activities. First, Stu2p binds to a single free tubulin heterodimer through its first TOG domain. A large conformational transition in homodimeric Stu2p from an open structure to a closed one accompanies the capture of a single free tubulin heterodimer. Second, Stu2p has the capacity to associate directly with microtubule ends, at least in part, through its second TOG domain. These two properties lead to the stabilization of microtubules in vivo, perhaps by the loading of tubulin dimers at microtubule ends. We suggest that this mechanism of microtubule regulation is a conserved feature of the Dis1/XMAP215 family of MAPs.

scholarly journals AB0566 NAILFOLD EXTENT OF REDUCED CAPILLARY DENSITY IS ASSOCIATED WITH DIGITAL ULCERS AND WITH AN INCREASED RISK OF DIGITAL ULCERS IN SYSTEMIC SCLEROSIS

2020 ◽  
Vol 79 (Suppl 1) ◽  
pp. 1580.2-1580
Author(s):  
R. De Angelis ◽  
F. Salaffi
Keyword(s):  
Systemic Sclerosis ◽  
Laboratory Data ◽  
Quantitative Measure ◽  
Capillary Density ◽  
Optical Probe ◽  
Typical Feature ◽  
Slight Reduction ◽  
Digital Ulcers ◽  
Increased Risk ◽  
Significant Difference

Background:A growing evidence supports the role of microvasculopathy as a primary pathogenic event in systemic sclerosis (SSc). The most commonly used imaging technique to identify microangiopathy in SSc is high magnification videocapillaroscopy (NVC), and reduced capillary density and/or capillary loss, which is a typical feature of “scleroderma microangiopathy”, easily identified by NVC, has been associated with digital ulcers (DUs). Different approaches have been proposed to measure capillary density or capillary loss. Some of these were qualitative methods, others semi-quantitative, others only concerned a limited nailfold area, without ever evaluating the overall density, which is more suitable for quantitative estimate.Objectives:To assess the association between the extent of different values of nailfold capillary density and the presence of DUs and to identify the risk of developing DUs, based on quantitative parameters.Methods:The study involved 54 SSc selected patients (47 women and 7 men, mean age 59.5 years, 50 with limited and 4 with diffuse). The study population came from an ongoing database, that includes clinical and laboratory data of patients with definite SSc. A videocapillaroscope (VideoCap® 3.0, DS Medica, Milan, Italy) with a 200x optical probe was used. During examination, eight fingers (fingers 2–5 of each hand), 4 fields per finger, according to the standard literature were assessed. For each patient, a total of 32 images were collected, then classified as having either “normal”, “non-specific” or the “scleroderma pattern” (SP). Capillary density was defined as the number of capillaries/mm in the distal row, regardless of its shape and morphology. Avascular areas were defined by the absence of loops within a width/area extending over more than 500 microns. For each patient, the SP images were further graded with no/slight reduction of the capillary density (7-9 loops/mm) (NOR), with a well-defined reduction of capillary density (6-4 loops/mm) (RED) and with loss of capillaries (<4) plus avascular areas (AA). Then, the overall percentages were calculated (the number with SP, the number with NOR, with RED and with AA, respect to 32), thus obtaining the quantitative measures. All data were analysed using the MedCalc® version 18.6; 64-bit (MedCalc Software, Mariakerke, Belgium).Results:A total of 1728 images were analyzed. Patients with DUs were 16/54 (29.6%). All patients had a SP, but only five patients showed a SP along the entire nailfold. A comparison between patients with or without DUs showed a significant difference both for the overall extent of AA (p=0.032), and particularly for the overall extent of RED (p<0.001). No significant difference was found regarding the overall extent of the SP (p=0.085). Factor significantly associated with DUs in multivariate analysis was the overall extent of RED (p=0.0286). The ROC curve was very effective at discriminating the capillary feature able to distinguish patients with DUs from patients without DUs. The discriminatory power of the overall extent of RED was very good, with an AUC of 0.948 (95 % CI 0.852 ± 0.990). Then, we calculated the cut-off values of the overall extent of RED for presence/absence of DUs with the highest combination of sensitivity and specificity. The resulting cut-off value (Yourden index of 0.825) was >68.7 (sensitivity 92.31 %; specificity 90.24 %) with a LR+ of 9.46.Conclusion:Our data strongly support that the capillary density between 4 and 6 loops/mm is the best capillaroscopic quantitative measure associated with DUs and able to discriminate the probability of having DUs. If all SSc-specific antibodies and/or other laboratory/clinical parameters are not yet available, the overall capillary density can allow physicians to assess SSc patients easily, regarding DUs and risk for developing DUs.Disclosure of Interests:None declared

scholarly journals A Radiometric Technique for Monitoring the Desulfurization Process of Blister Copper

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 842
Author(s):  
Alejandro Vásquez ◽  
Francisco Pérez ◽  
Maximiliano Roa ◽  
Ignacio Sanhueza ◽  
Hugo Rojas ◽  
...  
Keyword(s):  
Near Infrared ◽  
Spectral Emissivity ◽  
Optical Probe ◽  
Blister Copper ◽  
Optical Absorption Spectroscopy ◽  
Total Irradiance ◽  
Desulfurization Process ◽  
Radiometric Technique ◽  
Collimating Lens ◽  
Total Emissivity

In this paper, a novel optical technique for following the progress of the blister copper desulfurization process is presented. The technique is based on the changes observed in the continuous spectrum of the visible–near-infrared (VIS–NIR) radiation that the blister melt emits while the chemical reactions of the sulfur elimination process are taking place. Specifically, the proposed technique uses an optical probe composed of an optical fiber, a collimating lens, and a quartz tube, which is immersed in the melt. This optical probe provides a field of view of the blowing zone where the desulfurization reaction occurs. The experimental results show that the melt VIS–NIR total irradiance evolves inversely to the SO2 concentration reported by a gas analyzer based on differential optical absorption spectroscopy. Furthermore, the blister copper spectral emissivity as well as the total emissivity observed throughout the process show strong correlation with the sulfur content during desulfurization reaction.

scholarly journals DNA Aptamer Functionalized Hydrogels for Interferometric Fiber-Optic Based Continuous Monitoring of Potassium Ions

Biosensors ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 266
Author(s):  
Nataša Žuržul ◽  
Bjørn Torger Stokke
Keyword(s):  
Conformational Transition ◽  
Polymer Network ◽  
Potassium Ion ◽  
Ion Concentration ◽  
Dna Aptamer ◽  
Blood Levels ◽  
Label Free ◽  
Practical Applications ◽  
Hydrogel Matrix ◽  
K Concentration

In the present paper, we describe a potassium sensor based on DNA-aptamer functionalized hydrogel, that is capable of continuous label-free potassium ion (K+) monitoring with potential for in situ application. A hydrogel attached to the end of an optical fiber is designed with di-oligonucleotides grafted to the polymer network that may serve as network junctions in addition to the covalent crosslinks. Specific affinity toward K+ is based on exploiting a particular aptamer that exhibits conformational transition from single-stranded DNA to G-quadruplex formed by the di-oligonucleotide in the presence of K+. Integration of this aptamer into the hydrogel transforms the K+ specific conformational transition to a K+ concentration dependent deswelling of the hydrogel. High-resolution interferometry monitors changes in extent of swelling at 1 Hz and 2 nm resolution for the hydrogel matrix of 50 µm. The developed hydrogel-based biosensor displayed high selectivity for K+ ions in the concentration range up to 10 mM, in the presence of physiological concentrations of Na+. Additionally, the concentration dependent and selective K+ detection demonstrated in the artificial blood buffer environment, both at room and physiological temperatures, suggests substantial potential for practical applications such as monitoring of potassium ion concentration in blood levels in intensive care medicine.

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