Disulfides as redox switches : from molecular mechanisms to functional significance

The molecular mechanisms underlying thiol-based redox control are poorly defined. Disulfide bonds between Cys residues are commonly thought to confer extra rigidity and stability to their resident protein, forming a type of proteinaceous spot weld. Redox biologists have been redefining the role of disulfides over the last 30&ndash;40 years. Disulfides are now known to form in the cytosol under conditions of oxidative stress. Isomerization of extracellular disulfides is also emerging as an important regulator of protein function. The current paradigm is that the disulfide proteome consists of two subproteomes: a structural group and a redox-sensitive group. The redoxsensitive group is less stable and often associated with regions of stress in protein structures. Some characterized redox-active disulfides are the helical CXXC motif, often associated with thioredoxin-fold proteins; and forbidden disulfides, a group of metastable disulfides that disobey elucidated rules of protein stereochemistry. Here we discuss the role of redox-active disulfides as switches in proteins.<br /

A mild, efficient and catalyst-free thermoreversible ligation system based on dithiooxalates

We demonstrate a novel and ready to prepare thermoreversible hetero Diels–Alder dilinker on the basis of dithiooxalates, enabling the mild, rapid and catalyst-free linkage of diverse diene species under ambient conditions for applications in the fields of, for example, modular ligation, self-healing or recyclable materials and surface modification amongst others. The linker was studied using quantum chemical calculations, and experimentally in small molecular reactions via UV/Vis spectroscopy, mass spectrometry and NMR as well as in step-growth polymerizations with diene-difunctional building blocks – characterized via (temperature dependent) SEC and HT NMR – as an example for efficient polymer ligation

Insulin in motion: The A6-A11 disulfide bond allosterically modulates structural transitions required for insulin activity

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.The structural transitions required for insulin to activate its receptor and initiate regulation of glucose homeostasis are only partly understood. Here, using ring-closing metathesis, we substitute the A6-A11 disulfide bond of insulin with a rigid, non-reducible dicarba linkage, yielding two distinct stereo-isomers (cis and trans). Remarkably, only the cis isomer displays full insulin potency, rapidly lowering blood glucose in mice (even under insulin-resistant conditions). It also posseses reduced mitogenic activity in vitro. Further biophysical, crystallographic and molecular-dynamics analyses reveal that the A6-A11 bond configuration directly affects the conformational flexibility of insulin A-chain N-terminal helix, dictating insulin’s ability to engage its receptor. We reveal that in native insulin, contraction of the Cα-Cα distance of the flexible A6-A11 cystine allows the A-chain N-terminal helix to unwind to a conformation that allows receptor engagement. This motion is also permitted in the cis isomer, with its shorter Cα-Cα distance, but prevented in the extended trans analogue. These findings thus illuminate for the first time the allosteric role of the A6-A11 bond in mediating the transition of the hormone to an active conformation, significantly advancing our understanding of insulin action and opening up new avenues for the design of improved therapeutic analogues

Modeling Flexible Molecules in Solution: A p<i>K</i>_<i>a</i> Case Study

Continuum solvation models have been incredibly successful for the computationally efficient study of chemical reactions in solution. However, their development and application has generally been on focused on investigations of small, rigid molecules. Additional factors must be considered when studying large, flexible and multiply ionizable species. These include whether the use of thermocycle or entirely solution-phase approaches are more appropriate for the calculation of solution-phase free energies, which metrics can be used to reliably identify the conformation(s) adopted by flexible molecules in solution, and how errors due to inaccuracies in the prediction of low energy vibrational frequencies can be avoided. Here we explore these issues using the calculation of p<i>K</i>_<i>a</i>s for a diverse set of amine-containing species as a case study. We show that thermocycle-based approaches should only be applied where there are relatively small structural changes between the gas- and solution-phase molecular geometries, and that these methods are generally not appropriate for conformational searching. Using gas- or solution-phase energies or gas-phase free energies can also lead to errors in the identification of the most stable molecular conformation(s). Scaling of low energy vibrational modes (i.e., use of the quasi-harmonic oscillator approximation) is helpful, however care must be taken to ensure modes that change as part of the reaction are not disregarded. Entirely solution-phase approaches to the Gibbs free energy and hence p<i>K</i>_<i>a</i> calculations were found to yield accurate p<i>K</i>_<i>a</i> values for the amine test set studied when each charged site is complexed with an explicit water molecule and a proton exchange scheme is applied with an appropriately chosen reference acid

The effect of leaving radical on the formation of tetrahydroselenophene by SHi ring closure: an experimental and computational study

Competition kinetic studies augmented with laser-flash photolysis and high-level computational techniques [G3(MP2)-RAD], with [COSMO-RS, SMD] and without solvent correction, provide kinetic parameters for the ring closures of a series of 4-(alkylseleno)butyl radicals 1. At 22 °C rate constants (kc) that lie between 10(4)-10(7) s(-1) were determined experimentally and correlate with expectations based on leaving group ability. Activation energies (Eact) were determined to lie between 10.6 (R = Ph2CH) and 28.0 (R = n-Bu) kJ mol(-1), while log(A/s(-1)) values were generally between 9 and 10 in benzene. Computationally determined rate constants were in good-to-excellent agreement with those determined experimentally, with the COSMO-RS solvation model providing values that more closely resemble those from experiment than SMD.Generous support of the Australian Research Council through the Centres of Excellence Scheme is gratefully acknowledged. This research was undertaken with the assistance of resources provided at the NCI National Facility systems at the Australian National University through the National Computational Merit Allocation Scheme supported by the Australian Government. MLC also gratefully acknowledges financial support from the Australian Research Council and an ARC Future Fellowship