Active site geometry stabilization of a presenilin homolog by the lipid bilayer promotes intramembrane proteolysis

Cleavage of membrane proteins in the lipid bilayer by intramembrane proteases is crucial for health and disease. Although different lipid environments can potently modulate their activity, how this is linked to their structural dynamics is unclear. Here we show that the carboxy-peptidase-like activity of the archaeal intramembrane protease PSH, a homolog of the Alzheimer's disease-associated presenilin/γ-secretase is impaired in micelles and promoted in a lipid bilayer. Comparative molecular dynamics simulations revealed that important elements for substrate binding such as transmembrane domain 6a of PSH are more labile in micelles and stabilized in the lipid bilayer. Moreover, consistent with an enhanced interaction of PSH with a transition-state analog inhibitor, the bilayer promoted the formation of the enzyme's catalytic active site geometry. Our data indicate that the lipid environment of an intramembrane protease plays a critical role in structural stabilization and active site arrangement of the enzyme-substrate complex thereby promoting intramembrane proteolysis.

Characterization of Oregano Essential Oil (Origanum vulgare L. subsp. hirtum) Particles Produced by the Novel Nano Spray Drying Technique

Oregano essential oil (OEO), due to its wide variety of biological activities, could be a “green” alternative to chemical preservatives. On the other hand, the difficulties in its use or storage have turned researchers’ interest in encapsulation strategies as a way to face stability and handling issues. Fabrication of OEO-loaded particles, using nano spray drying technique (NSD) and whey protein isolate-maltodextrin mixtures (1:1, 1:3) as wall materials appears to be a novel and promising strategy. The obtained particles were characterized in terms of volatile composition, encapsulation efficiency, and physicochemical, molecular, morphological, and antibacterial properties. The results confirmed that encapsulation of OEO using NSD achieved high levels of powder recovery (>77%) and encapsulation efficiency (>98%) while assisting in the retention of the main bioactive compounds. The partial replacement of WPI by MD significantly affected particles’ physical properties. FTIR analyses revealed the possible structural stabilization of core and wall materials, while SEM verified the very fine size and spherical shape. Finally, antibacterial studies demonstrated their activity against Escherichia coli and Staphylococcus aureus, which is much stronger in comparison with that of pure OEO, proving the positive effect of NSD and particles’ potential in future food applications.

Yeast-Based Directed-Evolution For High-Throughput Structural Stabilization of G Protein-Coupled Receptors (GPCRs)

The immense potential of G protein-coupled receptors (GPCRs) as targets for drug discovery is not fully realized due to the enormous difficulties associated with structure elucidation of these profoundly unstable membrane proteins. The existing methods of GPCR stability-engineering are cumbersome and low-throughput; in addition, the scope of GPCRs that could benefit from these techniques is limited. Here, we presented a yeast-based screening platform for a single-step isolation of GRCR variants stable in the presence of short-chain detergents, a feature essential for their successful crystallization using vapor diffusion method. The detergent-resistant cell wall of yeast provides a unique compartmentalization opportunity to physically link the receptor phenotype to its encoding DNA, and thus enable discovery of stable GPCR variants with unprecedent efficiency. The scope of mutations identified by the method offers important insights into the structural basis of GPCR stability, questioning the inherent instability of the GPCR scaffold, and revealing the potential role of the C-terminus in receptor stabilization.

Backstepping Global and Structural Stabilization of DC/DC Boost Converter

This paper deals with the stabilization of DC/DC boost converter and the nonlinear phenomena elimination using a constrained Backstepping technique. Based on the converter averaged model, the pro- posed control approach is designed and the input to state stability concept is used to proof the system global stability. Furthermore, the structural stability is proven to show the efficiency of the proposed approach to suppress the nonlinear phenomena exhibited by the converter. The simulation results illustrate the different regions of stability of the system and the bifurcation diagrams are given to show the effectiveness of the proposed approach in terms of nonlinear phenomena suppression.

Structural insights into the gating mechanism of human Cx43/GJA1 gap junction channel

Connexin family proteins assemble into hexameric hemichannels in a cell membrane, which dock together between two adjacent membranes to form gap junction intercellular channels (GJIChs). The most ubiquitously expressed connexin Cx43 plays important roles in numerous biological processes. Here we report cryo-EM structures of Cx43 GJIChs at 3.1–3.6 Å resolutions, which show dynamic conformational changes of N-terminal helices (NTHs) caused by pH change or C-terminal truncation. Cx43 GJIChs in a channel-closing condition contain 12 protomers in gate-covering NTH (GCN) conformation, while those in opening conditions have varying compositions of GCNs and pore-lining NTHs (PLNs) resulting in various pore dimensions and electrostatic surface potentials. GCN-to-PLN transition accompanies π-helix formation in the first transmembrane helix (TM1), movement of TM2-4 that creates a side opening to the membrane, and structural stabilization of the cytoplasmic loop. Our study provides structural insights into the intercellular ion/metabolite transfer and the lateral lipid transport through Cx43 GJICh.

Introduction of the Carotenoid Biosynthesis α-Branch Into Synechocystis sp. PCC 6803 for Lutein Production

Lutein, made by the α-branch of the methyl-erythritol phosphate (MEP) pathway, is one of the most abundant xanthophylls in plants. It is involved in the structural stabilization of light-harvesting complexes, transfer of excitation energy to chlorophylls and photoprotection. In contrast, lutein and the α-branch of the MEP pathway are not present in cyanobacteria. In this study, we genetically engineered the cyanobacterium Synechocystis for the missing MEP α-branch resulting in lutein accumulation. A cassette comprising four Arabidopsis thaliana genes coding for two lycopene cyclases (AtLCYe and AtLCYb) and two hydroxylases (AtCYP97A and AtCYP97C) was introduced into a Synechocystis strain that lacks the endogenous, cyanobacterial lycopene cyclase cruA. The resulting synlut strain showed wild-type growth and only moderate changes in total pigment composition under mixotrophic conditions, indicating that the cruA deficiency can be complemented by Arabidopsis lycopene cyclases leaving the endogenous β-branch intact. A combination of liquid chromatography, UV-Vis detection and mass spectrometry confirmed a low but distinct synthesis of lutein at rates of 4.8 ± 1.5 nmol per liter culture at OD730 (1.03 ± 0.47 mmol mol–1 chlorophyll). In conclusion, synlut provides a suitable platform to study the α-branch of the plastidic MEP pathway and other functions related to lutein in a cyanobacterial host system.

Chemical Modulation of Local Transition Metal Environment Enables Reversible Oxygen Redox in Mn-Based Layered Cathodes

<p>Oxygen redox plays a prominent role in enhancing the energy density of Mn-based layered cathodes. However, understanding the factors affecting the reversibility of oxygen redox is nontrivial due to the complicated concurrent structural and chemical transformations. Herein, we show that local Mn‒O symmetry induced structural and chemical evolutions majorly dictate the reversibility of oxygen redox of Na_xLi_yMn_1-yO₂ in Na cells. We find that Na_xLi­_yMn_1-yO₂ with Jahn-Teller distorted MnO₆ octahedra undergoes severe Mn dissolution during cycling, which destabilizes the transition metal layer resulting in poor Li retention and irreversible oxygen redox. Jahn-Teller distortion of MnO₆ octahedra can be suppressed by modulating the local charge of Mn and Mn‒O distance through Mg/Ti dual doping. This leads to reduced Mn dissolution resulting in more reversible oxygen redox. Such stabilization significantly improves the electrochemical performance of Mg/Ti dual doped Na_xLi_yMn_1-yO₂. Through this work, we show that promoting reversible oxygen redox can benefit from structural stabilization at local length scale, and that modifying the chemical environment through doping chemistry is an efficient strategy to promote local structural stability and thus, oxygen redox.</p>

Chemical Modulation of Local Transition Metal Environment Enables Reversible Oxygen Redox in Mn-Based Layered Cathodes

<p>Oxygen redox plays a prominent role in enhancing the energy density of Mn-based layered cathodes. However, understanding the factors affecting the reversibility of oxygen redox is nontrivial due to the complicated concurrent structural and chemical transformations. Herein, we show that local Mn‒O symmetry induced structural and chemical evolutions majorly dictate the reversibility of oxygen redox of Na_xLi_yMn_1-yO₂ in Na cells. We find that Na_xLi­_yMn_1-yO₂ with Jahn-Teller distorted MnO₆ octahedra undergoes severe Mn dissolution during cycling, which destabilizes the transition metal layer resulting in poor Li retention and irreversible oxygen redox. Jahn-Teller distortion of MnO₆ octahedra can be suppressed by modulating the local charge of Mn and Mn‒O distance through Mg/Ti dual doping. This leads to reduced Mn dissolution resulting in more reversible oxygen redox. Such stabilization significantly improves the electrochemical performance of Mg/Ti dual doped Na_xLi_yMn_1-yO₂. Through this work, we show that promoting reversible oxygen redox can benefit from structural stabilization at local length scale, and that modifying the chemical environment through doping chemistry is an efficient strategy to promote local structural stability and thus, oxygen redox.</p>

A New Drug Discovery Approach Based on Thermal Proteome Profiling to Develop More Effective Drugs

: The search for disease-related targets and studying drug-protein and protein-protein interactions are central issues that would accelerate the clinical approval of a drug. Also, by developing an accurate method in this regard, time and resource consumption will significantly decrease. The low efficiency of some drugs in humans is a grave issue leading to a low rate of FDA approval after spending billions of dollars and decades of research. Several strategies and methods have been expanded to fill this gap, such as drug affinity responsive target stability (DARTS), stability of proteins from rates of oxidation (SPROX), cellular thermal shift assay (CETSA), and finally, thermal proteome profiling (TPP). The TPP is based on the combination of CETSA and quantitative mass spectrometry. Among recently introduced proteomics technologies, TPP demonstrates the ability to offer detailed proteomic profiles for the large-scale analysis of protein-ligand interactions, including endogenous ligands and proteins like cofactors and metabolites. TPP facilitates the identification of the markers governing drug efficacy and toxicity and provides an unbiased measure for estimating the rate of drug-target engagement. At a glance at TPP steps, after protein extraction, the molecule is exposed to different temperatures and drug concentrations. After discarding solubilized and stabilized proteins, the protein’s identity is investigated by mass spectrometry analysis. As a result of the protein’s structural stabilization after binding to its substrate, TTP helps to accurately identify target proteins with high throughput. In this study, we aimed to introduce the basics of this method and review most recent studies on this technique.