Selective labeling of peptides, metalloproteins, and proteolytic enzymes with Pt(II) complexes and electron-transfer reactions of native and cross-linked metalloproteins

The transition-metal complex (Pt(trpy)Cl) [superscript]+ selectively labels the amino acids Cys and His, but is unreactive toward Met. The (Pt(trpy)Cl) [superscript]+ complex also forms complexes with nonbiological ligands to form novel compounds with metal-metal or [pi]-[pi] interactions;The homologous gold reagent, (Au(trpy)Cl) [superscript]2+ reacts with Trp, Cys, His, and Met. The oxidative properties of the gold complex makes it an invasive reagent toward proteins, however;In reactions with proteins, the complex (Pt(trpy)Cl) [superscript]+ exhibits unexpected selectivity toward amino acid side chains in cytochromes c. His residues are labeled in greater yield than the Cys residues. The Pr(trpy)[superscript]2+ tags are stable and are easily detected and quantitated. The new reagent does not alter the structural and redox properties of the cytochromes c;Subsequent research involves modification of the active sites of serine and sulfhydryl proteases with (Pt(trpy)Cl) [superscript]+. Although the tagging modifies the catalytic triad and disrupts the charge relay, the platinated enzymes retain significant activity for substrates. The (Pt(trpy)Cl) [superscript]+ complex labels both Cys and His residues in papain. Selective removal of these tags with judiciously chosen nucleophiles provides a new approach for site-selective modification of proteins;Cyt c was also modified with the negatively charged complex (Pt(sbpaphy)Cl) [superscript]-. The yield of protein derivatives is low compared with (Pt(trpy)Cl) [superscript]+ derivatives;Electron-transfer between covalently tethered cyt c and pc is investigated. The tethers prohibit surface diffusion of the proteins and therefore prohibit a productive electron-transfer complex from forming. Rates of electron transfer between the heterodimeric proteins and a third, free, monomeric protein provide an empirical approach for understanding how the 2 proteins are cross-linked and why they cannot participate in intracomplex electron transfer;Methylene blue has long been known to be a photoreductant, but its reactions with biomolecules have not been quantitated. Rates of reaction of methylene blue and derivatives of methylene blue with cyt c are measured

Contingency and Its Intersections in Writing Centers: An Introduction

Introduction to WCJ 41.1, which is a special issue on contingency in writing centers

Contingent Writing Center Work: Benefits, Risks, and the Need for Equity and Institutional Change

This study investigates and reports on the personal, professional, and programmatic benefits and risks associated with contingent writing center work. Interviews were conducted with 48 contingent writing centers workers, including directors, assistant directors, associate directors, graduate student workers, and tutors. Survey data of the interview participants showed contingent writing center workers are usually White women with advanced degrees. Most of this article focuses on interview data, analyzed using grounded theory. Interviews revealed participants’ understanding of what contingency means and revealed their struggles with instability, insecurity, and uncertainty even while they lauded the flexibility, freedom, and autonomy their contingency afforded them. The interview data also further revealed the ways in which these working conditions were created and maintained by the institution. These findings suggest the need for collective action across the composition and writing center fields—from professional organizations, tenure-line writing center workers, and contingent workers themselves. Through collective action, we can create equitable working conditions for all writing center workers

Noise-based core monitoring and diagnostics: overview of the cortex project

This paper gives an overview of the CORTEX project, which is a Research and Innovation Action funded by the European Union in the Euratom 2016-2017 work program, under the Horizon 2020 framework. CORTEX, which stands for CORe monitoring Techniques and EXperimental validation and demonstration, aims at developing an innovative core monitoring technique that allows detecting anomalies in nuclear reactors, such as excessive vibrations of core internals, flow blockage, coolant inlet perturbations, etc. The technique is based on primarily using the inherent fluctuations in neutron flux recorded by in-core and ex-core instrumentation (often referred to as neutron noise), from which the anomalies will be differentiated depending on their type, location and characteristics. In addition to be non-intrusive and not requiring any external perturbation of the system, the method allows the detection of operational problems at a very early stage. Proper actions could thus be taken by utilities before such problems have any adverse effect on plant safety and reliability

Polymorphism and selection of rpoS in pathogenic Escherichia coli

<p>Abstract</p> <p>Background</p> <p>Though RpoS is important for survival of pathogenic <it>Escherichia coli </it>in natural environments, polymorphism in the <it>rpoS </it>gene is common. However, the causes of this polymorphism and consequential physiological effects on gene expression in pathogenic strains are not fully understood.</p> <p>Results</p> <p>In this study, we found that growth on non-preferred carbon sources can efficiently select for loss of RpoS in seven of ten representative verocytotoxin-producing <it>E. coli </it>(VTEC) strains. Mutants (Suc⁺⁺) forming large colonies on succinate were isolated at a frequency of 10^-8mutants per cell plated. Strain O157:H7 EDL933 yielded mainly mutants (about 90%) that were impaired in catalase expression, suggesting the loss of RpoS function. As expected, inactivating mutations in <it>rpoS </it>sequence were identified in these mutants. Expression of two pathogenicity-related phenotypes, cell adherence and RDAR (red dry and rough) morphotype, were also attenuated, indicating positive control by RpoS. For the other Suc⁺⁺mutants (10%) that were catalase positive, no mutation in <it>rpoS </it>was detected.</p> <p>Conclusion</p> <p>The selection for loss of RpoS on poor carbon sources is also operant in most pathogenic strains, and thus is likely responsible for the occurrence of <it>rpoS </it>polymorphisms among <it>E. coli </it>isolates.</p

Towards Quantum Sensing of Chiral-Induced Spin Selectivity: Probing Donor-Bridge-Acceptor Molecules with NV Centers in Diamond

Photoexcitable donor-bridge-acceptor (D-B-A) molecules that support intramolecular charge transfer are ideal platforms to probe the influence of chiral-induced spin selectivity (CISS) in electron transfer and resulting radical pairs. In particular, the extent to which CISS influences spin polarization or spin coherence in the initial state of spin-correlated radical pairs following charge transfer through a chiral bridge remains an open question. Here, we introduce a quantum sensing scheme to measure directly the hypothesized spin polarization in radical pairs using shallow nitrogen-vacancy (NV) centers in diamond at the single- to few-molecule level. Importantly, we highlight the perturbative nature of the electron spin-spin dipolar coupling within the radical pair, and demonstrate how Lee-Goldburg decoupling can preserve spin polarization in D-B-A molecules for enantioselective detection by a single NV center. The proposed measurements will provide fresh insight into spin selectivity in electron transfer reactions.Comment: 7 pages and 4 pages appendix including an extensive description of the initial spin state of photo-generated radical pair

Tracking the precession of single nuclear spins by weak measurements

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for analyzing the structure and function of molecules, and for performing three-dimensional imaging of the spin density. At the heart of NMR spectrometers is the detection of electromagnetic radiation, in the form of a free induction decay (FID) signal, generated by nuclei precessing around an applied magnetic field. While conventional NMR requires signals from 1e12 or more nuclei, recent advances in sensitive magnetometry have dramatically lowered this number to a level where few or even individual nuclear spins can be detected. It is natural to ask whether continuous FID detection can still be applied at the single spin level, or whether quantum back-action modifies or even suppresses the NMR response. Here we report on tracking of single nuclear spin precession using periodic weak measurements. Our experimental system consists of carbon-13 nuclear spins in diamond that are weakly interacting with the electronic spin of a nearby nitrogen-vacancy center, acting as an optically readable meter qubit. We observe and minimize two important effects of quantum back-action: measurement-induced decoherence and frequency synchronization with the sampling clock. We use periodic weak measurements to demonstrate sensitive, high-resolution NMR spectroscopy of multiple nuclear spins with a priori unknown frequencies. Our method may provide the optimum route for performing single-molecule NMR at atomic resolution.Comment: 29 pages including methods and extended data figures; for supplementary material, see v1 of this submissio

Asymptotics and local constancy of characters of p-adic groups

In this paper we study quantitative aspects of trace characters $\Theta_\pi$ of reductive $p$-adic groups when the representation $\pi$ varies. Our approach is based on the local constancy of characters and we survey some other related results. We formulate a conjecture on the behavior of $\Theta_\pi$ relative to the formal degree of $\pi$, which we are able to prove in the case where $\pi$ is a tame supercuspidal. The proof builds on J.-K.~Yu's construction and the structure of Moy-Prasad subgroups.Comment: Proceedings of Simons symposium on the trace formul