Making and breaking disulfide bonds

Cofilin-Mediated Filament Softening and Crosslinking Counterbalance to Enhance Actin Network Flexibility

Filamentous-actin (F-actin) crosslinking within the cell cytoskeleton mediates the transmission of mechanical forces, enabling changes in cell shape, as occurs during cell division and cell migration. Crosslinking by actin binding proteins (ABPs) generally increases the connectivity of the F-actin network, but also increases network rigidity. As a result, there is a narrow range in the concentration of crosslinker protein at which F-actin networks are both connected and labile. Another ABP, cofilin, severs F-actin filaments at high pH through increasing their bending flexibility and concentrating mechanical stress, inducing fragmentation. By contrast, at lower pH, cofilin increases filament flexibility yet does not sever. Instead, it forms disulfide bonds, which crosslink F-actin into bundles, and bundles into networks. Here, we combine light microscopy and rheology to determine the impact of two potentially opposing effects on the mechanics of F-actin networks-increased flexibility at the filament level, and increased connectivity at the network level. Indeed, by linear rheology, we find that these mechanisms are counterbalanced, such that cofilactin network moduli are only weakly dependent on cofilin concentration over a broad range, in contrast to the dramatic stiffening that occurs with F-actin crosslinking protein. Further, by nonlinear rheology, the network stiffens at a higher stress than crosslinking protein, indicative of a broader range in which the material remains flexible. These results may enable F-actin networks to increase connectivity without heavy penalties to rigidity, and thus provide a new route to modulating active polymer mechanics unseen using traditional F-actin accessory proteins.

Rational enzyme design by reducing the number of hotspots and library size

Biocatalysts that are eco-friendly, sustainable, and highly specific have great potential for applications in the production of fine chemicals, food, detergents, biofuels, pharmaceuticals, and more. However, due to factors such as low activity, narrow substrate scope, poor thermostability, or incorrect selectivity, most natural enzymes cannot be directly used for large-scale production of the desired products. To overcome these obstacles, protein engineering methods have been developed over decades and have become powerful and versatile tools for adapting enzymes with improved catalytic properties or new functions. The vastness of the protein sequence space makes screening a bottleneck in obtaining advantageous mutated enzymes in traditional directed evolution. In the realm of mathematics, there are two major constraints in the protein sequence space: (1) the number of residue substitutions (M); and (2) the number of codons encoding amino acids as building blocks (N). This feature review highlights protein engineering strategies to reduce screening efforts from two dimensions by reducing the numbers M and N, and also discusses representative seminal studies of rationally engineered natural enzymes to deliver new catalytic functions.

Anisamide-conjugated hairpin antisense oligonucleotides prodrug co-delivering doxorubicin exhibited enhanced anticancer efficacy

Antisense oligonucleotides (ASONs)-based therapeutics offers tremendous promise for the treatment of diverse diseases. However, there is still a need to develop ASONs with enhanced stability against enzymes, improved drug delivery, and enhanced biological potency. In this study, we propose a novel anisamide (AA)-conjugated hairpin oligonucleotide prodrug loading with chemotherapeutic agent (doxorubicin, DOX) (AA-loop-ASON/DOX) for oncotherapy. Results indicated that the introduction of a hairpin conformation and AA ligand in prodrug significantly improved the stability against enzymatic hydrolysis, as well as the cellar uptake of ASONs and DOX. The incorporation of disulfide bonds could trigger mechanical opening, resulting in the release of ASON and DOX in response to the intracellular glutathione (GSH) in tumors. Moreover, the composite of DOX-loading ASONs prodrug exhibited a robust and selective inhibition of tumor cell proliferation. This paper introduces a novel design concept for nucleic acid-based therapeutics, aiming to enhance the delivery of drug and improve biological effectiveness.

Hypoxia-inducible factor induces cysteine dioxygenase and promotes cysteine homeostasis in Caenorhabditis elegans

Dedicated genetic pathways regulate cysteine homeostasis. For example, high levels of cysteine activate cysteine dioxygenase, a key enzyme in cysteine catabolism in most animal and many fungal species. The mechanism by which cysteine dioxygenase is regulated is largely unknown. In an unbiased genetic screen for mutations that activate cysteine dioxygenase (cdo-1) in the nematode Caenorhabditis elegans, we isolated loss-of-function mutations in rhy-1 and egl-9, which encode proteins that negatively regulate the stability or activity of the oxygen-sensing hypoxia inducible transcription factor (hif-1). EGL-9 and HIF-1 are core members of the conserved eukaryotic hypoxia response. However, we demonstrate that the mechanism of HIF-1-mediated induction of cdo-1 is largely independent of EGL-9 prolyl hydroxylase activity and the von Hippel-Lindau E3 ubiquitin ligase, the classical hypoxia signaling pathway components. We demonstrate that C. elegans cdo-1 is transcriptionally activated by high levels of cysteine and hif-1. hif-1-dependent activation of cdo-1 occurs downstream of an H2S-sensing pathway that includes rhy-1, cysl-1, and egl-9. cdo-1 transcription is primarily activated in the hypodermis where it is also sufficient to drive sulfur amino acid metabolism. Thus, the regulation of cdo-1 by hif-1 reveals a negative feedback loop that maintains cysteine homeostasis. High levels of cysteine stimulate the production of an H2S signal. H2S then acts through the rhy-1/cysl-1/egl-9 signaling pathway to increase HIF-1-mediated transcription of cdo-1, promoting degradation of cysteine via CDO-1.

Heat Shock Protein Network: the Mode of Action, the Role in Protein Folding and Human Pathologies

Protein folding is an extremely complicated process, which has been extensively tackled during the last decades. In vivo, a certain molecular machinery is responsible for assisting the correct folding of proteins and maintaining protein homeostasis: the members of this machinery are the heat shock proteins (HSPs), which belong among molecular chaperones. Mutations in HSPs are associated with several inherited diseases, and members of this group were also proved to be involved in neurodegenerative pathologies (e.g., Alzheimer and Parkinson diseases), cancer, viral infections, and antibiotic resistance of bacteria. Therefore, it is critical to understand the principles of HSP functioning and their exact role in human physiology and pathology. This review attempts to briefly describe the main chaperone families and the interplay between individual chaperones, as well as their general and specific functions in the context of cell physiology and human diseases.

Hypoxia-inducible factor induces cysteine dioxygenase and promotes cysteine homeostasis in Caenorhabditis elegans

Dedicated genetic pathways regulate cysteine homeostasis. For example, high levels of cysteine activate cysteine dioxygenase, a key enzyme in cysteine catabolism in most animal and many fungal species. The mechanism by which cysteine dioxygenase is regulated is largely unknown. In an unbiased genetic screen for mutations that activate cysteine dioxygenase (cdo-1) in the nematode C. elegans, we isolated loss-of-function mutations in rhy-1 and egl-9, which encode proteins that negatively regulate the stability or activity of the oxygen-sensing hypoxia inducible transcription factor (hif-1). EGL-9 and HIF-1 are core members of the conserved eukaryotic hypoxia response. However, we demonstrate that the mechanism of HIF-1-mediated induction of cdo-1 is largely independent of EGL-9 prolyl hydroxylase activity and the von Hippel-Lindau E3 ubiquitin ligase, the classical hypoxia signaling pathway components. We demonstrate that C. elegans cdo-1 is transcriptionally activated by high levels of cysteine and hif-1. hif-1-dependent activation of cdo-1 occurs downstream of an H2S-sensing pathway that includes rhy-1, cysl-1, and egl-9. cdo-1 transcription is primarily activated in the hypodermis where it is also sufficient to drive sulfur amino acid metabolism. Thus, the regulation of cdo-1 by hif-1 reveals a negative feedback loop that maintains cysteine homeostasis. High levels of cysteine stimulate the production of an H2S signal. H2S then acts through the rhy-1/cysl-1/egl-9 signaling pathway to increase HIF-1-mediated transcription of cdo-1, promoting degradation of cysteine via CDO-1.

Finite temperature string method with umbrella sampling using path collective variables: application to secondary structure change in a protein

The transition of an α-helix to a β-sheet in proteins is among the most complex conformational changes seen in biomolecular systems. Due to long time scales involved in the transition, it is challenging to study such protein conformational changes using direct molecular dynamics simulations. This limitation is typically overcome using an indirect approach wherein one computes the free energy landscape associated with the transition. Computation of free energy landscapes, however, requires a suitable set of collective variables that describe the transition. In this work, we demonstrate the use of path collective variables [D. Branduardi, F. L. Gervasio and M. Parrinello, J. Chem. Phys., 2007, 126, 054103] and combine it with the finite temperature string (FTS) method [E. Weinan, W. Ren and E. Vanden-Eijnden, J. Phys. Chem. B, 2005, 109, 6688-6693] to determine the molecular mechanisms involved during the structural transition of the mini G-protein from an α-helix to a β-hairpin. The transition from the α-helix proceeds via unfolding of the terminal residues, giving rise to a β-turn unfolded intermediate to eventually form the β-hairpin. Our proposed algorithm uses umbrella sampling simulations to simulate images along the string and the weighted histogram analysis to compute the free energy along the computed transition path. This work demonstrates that the string method in combination with path collective variables can be exploited to study complex protein conformational changes such as a complete change in the secondary structure.

Pathogen-derived peptides in drug targeting and its therapeutic approach

Peptides, short stretches of amino acids or small proteins that occupy a strategic position between proteins and amino acids, are readily accessible by chemical and biological methods. With ideal properties for forming high-affinity and specific interactions with host target proteins, they have established an important niche in the drug development spectrum complementing small molecule and biological therapeutics. Among the most successful biomedicines in use today, peptide-based drugs show great promise. This, coupled with recent advances in synthetic and nanochemical biology, has led to the creation of tailor-made peptide therapeutics for improved biocompatibility. This review presents an overview of the latest research on pathogen-derived, host-cell-interacting peptides. It also highlights strategies for using peptide-based therapeutics that address cellular transport challenges through the introduction of nanoparticles that serve as platforms to facilitate the delivery of peptide biologics and therapeutics for treating various inflammatory diseases. Finally, this paper describes future perspectives, specific pathogen-based peptides that can enhance specificity, efficiency, and capacity in functional peptide-based therapeutics, which are in the spotlight as new treatment alternatives for various diseases, and also presents verified sequences and targets that can increase chemical and pharmacological value.

Redox-responsive self-assembled polymeric nanoprodrug for delivery of gemcitabine in B-cell lymphoma therapy

Gemcitabine, as a standard and classic strategy for B-cell lymphoma in the clinic, is limited by its poor pharmacodynamics. Although stimuli-responsive polymeric nanodelivery systems have been widely investigated in the past decade, issues such as complicated procedures, low loading capacity, and uncontrollable release kinetics still hinder their clinical translation. In view of the above considerations, we attempt to construct hyperbranched polyprodrug micelles with considerable drug loading via simple procedures and make use of the particularity of the tumor microenvironment to ensure that the micelles are "inactivated" in normal tissues and "activated" in the tumor microenvironment. Hence, in this work, a redox-responsive polymeric gemcitabine-prodrug (GEM-S-S-PEG) was one-pot synthesized via facile esterification and acylation. The self-assembled subsize (< 100 nm) GEM-S-S-PEG (GSP NPs) with considerable loading capacity (≈ 24.6%) exhibited on-demand and accurate control of gemcitabine release under a simulated tumor microenvironment and thus significantly induced the apoptosis of B-cell lymphoma in vitro. Moreover, in the A20 tumor xenograft murine model, GSP NPs efficiently decreased the expansion of tumor tissues with minimal systemic toxicity. In summary, these redox-responsive and self-assembling GSP NPs with a facile one-pot synthesis procedure may hold great potency in clinical translation for enhanced chemotherapy of B-cell lymphoma. STATEMENT OF SIGNIFICANCE: A redox-responsive polymeric gemcitabine-prodrug (GEM-S-S-PEG) was one-pot synthesized via facile esterification and acylation. The self-assembled subsize (< 100 nm) GEM-S-S-PEG (GSP NPs) exhibited significant tumor therapeutic effects in vitro and in vivo. The polyprodrug GEM-S-S-PEG prepared in this study shows the great potential of redox-responsive nanodrugs for antitumor activity, which provides a reference value for the optimization of the design of functional polyprodrugs.

Supramolecular nanoparticles self-assembled from reduction-responsive cabazitaxel prodrugs for effective cancer therapy

Using hydrophobic cabazitaxel as a target anticancer drug, we show that the conjugation of oligo(ethylene glycol)-oligolactide (OEG-OLA) via a self-immolative linkage induces the self-assembly of the resulting prodrug into injectable nanoparticles. The nanoparticles release chemically unmodified cabazitaxel after endocytosis in cancer cells. With the optimal conjugate, the nanotherapy not only potently induces tumor regression but also has a higher safety margin in animals than the free drug administered in its clinical formulation. Our studies highlight the design rationale that attaching a short amphiphilic oligomer to a toxic drug can convert it to a self-deliverable and safe nanotherapy.

A Tale of Drug-Carrier Optimization: Controlling Stimuli Sensitivity via Nanoparticle Hydrophobicity through Drug Loading

Interactions between drug molecules, nanocarrier components, and surrounding media influence the properties and therapeutic efficacies of nanomedicines. In this study, we investigate the role that reversible covalent loading of a hydrophobic drug exerts on intra-nanoparticle physical properties and explore the utility of this payload control strategy for tuning the access of active agents and, thereby, the stimuli sensitivity of smart nanomaterials. Glutathione sensitivity was controlled via altering the degree of hydrophobic payload loading of disulfide-linked camptothecin-conjugated sugar-based nanomaterials. Increases in degrees of camptothecin conjugation (f_CPT) decreased aqueous accessibility and reduced glutathione-triggered release. Although the lowest f_CPT gave the fastest camptothecin release, it resulted in the lowest camptothecin concentration. Remarkably, the highest f_CPT resulted in a 5.5-fold improved selectivity against cancer vs noncancerous cells. This work represents an advancement in drug carrier design by demonstrating the importance of controlling the amount of drug loading on the overall payload and its availability.

Protein Disulfide Exchange by the Intramembrane Enzymes DsbB, DsbD, and CcdA

The formation of disulfide bonds in proteins is an essential process in both prokaryotes and eukaryotes. In gram-negative bacteria including Escherichia coli, the proteins DsbA and DsbB mediate the formation of disulfide bonds in the periplasm. DsbA acts as the periplasmic oxidant of periplasmic substrate proteins. DsbA is reoxidized by transfer of reducing equivalents to the 4 TM helix membrane protein DsbB, which transfers reducing equivalents to ubiquinone or menaquinone. Multiple structural studies of DsbB have provided detailed structural information on intermediates in the process of DsbB catalyzed oxidation of DsbA. These structures and the insights gained are described. In proteins with more than one pair of Cys residues, there is the potential for formation of non-native disulfide bonds, making it necessary for the cell to have a mechanism for the isomerization of such non-native disulfide bonds. In E. coli, this is mediated by the proteins DsbC and DsbD. DsbC reduces mis-formed disulfide bonds. The eight-TM-helix protein DsbD reduces DsbC and is itself reduced by cytoplasmic thioredoxin. DsbD also contributes reducing equivalents for the reduction of cytochrome c to facilitate heme attachment. The DsbD functional homolog CcdA is a six-TM-helix membrane protein that provides reducing equivalents for the reduction of cytochrome c. A recent structure determination of CcdA has provided critical insights into how reducing equivalents are transferred across the membrane that likely also provides understanding how this is achieved by DsbD as well. This structure and the insights gained are described.

Rhodium-Catalyzed Synthesis of Organosulfur Compounds Involving S-S Bond Cleavage of Disulfides and Sulfur

Organosulfur compounds are widely used for the manufacture of drugs and materials, and their synthesis in general conventionally employs nucleophilic substitution reactions of thiolate anions formed from thiols and bases. To synthesize advanced functional organosulfur compounds, development of novel synthetic methods is an important task. We have been studying the synthesis of organosulfur compounds by transition-metal catalysis using disulfides and sulfur, which are easier to handle and less odiferous than thiols. In this article, we describe our development that rhodium complexes efficiently catalyze the cleavage of S-S bonds and transfer organothio groups to organic compounds, which provide diverse organosulfur compounds. The synthesis does not require use of bases or organometallic reagents; furthermore, it is reversible, involving chemical equilibria and interconversion reactions.

Stimuli-responsive Drug Delivery Nanocarriers in the Treatment of Breast Cancer

Stimuli-responsive drug-delivery nanocarriers (DDNs) have been increasingly reported in the literature as an alternative for breast cancer therapy. Stimuli-responsive DDNs are developed with materials that present a drastic change in response to intrinsic/chemical stimuli (pH, redox and enzyme) and extrinsic/physical stimuli (ultrasound, Near-infrared (NIR) light, magnetic field and electric current). In addition, they can be developed using different strategies, such as functionalization with signaling molecules, leading to several advantages, such as (a) improved pharmaceutical properties of liposoluble drugs, (b) selectivity with the tumor tissue decreasing systemic toxic effects, (c) controlled release upon different stimuli, which are all fundamental to improving the therapeutic effectiveness of breast cancer treatment. Therefore, this review summarizes the use of stimuli-responsive DDNs in the treatment of breast cancer. We have divided the discussions into intrinsic and extrinsic stimuli and have separately detailed them regarding their definitions and applications. Finally, we aim to address the ability of these stimuli-responsive DDNs to control the drug release in vitro and the influence on breast cancer therapy, evaluated in vivo in breast cancer models.

Development of dual-targeted nano-dandelion based on an oligomeric hyaluronic acid polymer targeting tumor-associated macrophages for combination therapy of non-small cell lung cancer

In this study, the novel carrier materials were screened to structure targeting nano-micelles (named ‘nano-dandelion’) for synchronous delivery of curcumin (Cur) and baicalin (Bai), which could effectively overcome the tumor resistance. Mannose (Man) was found to bind better to CD206 receptors on the surface of tumor-associated macrophages (TAMs), thereby increasing the number of nano-dandelion engulfed by TAMs. Furthermore, oligomeric hyaluronic acid (oHA) was able to target CD44 receptors, resulting in recruitment of a higher number of nano-dandelion to locate and engulf tumor cells. The disulfide bond (S–S) in 3,3′-dithiodipropionic acid (DA) could be broken by the high concentration of glutathione (GSH) in the tumor microenvironment (TME). Based on this, we selected DA to connect hydrophobic fragments (quercetin, Que) and oHA. A reduction-sensitive amphiphilic carrier material, quercetin–dithiodipropionic acid–oligomeric hyaluronic acid–mannose–ferulic acid (Que–S–S–oHA–Man–FA; QHMF) was fabricated and synthesized by ¹H NMR. Next, QHMF self-assembled into nano-dandelion, i.e. encapsulated Cur and Bai in water. Critical experimental conditions in the preparation process of nano-dandelion that could affect its final properties were explored. Nano-dandelion with a small particle size (121.0 ± 15 nm) and good normal distribution (PI = 0.129) could easily enter tumor tissue through vascular barrier. In addition, nano-dandelion with a suitable surface potential (–20.33 ± 4.02 mV) could remain stable for a long duration. Furthermore, good cellular penetration and tumor cytotoxicity of nano-dandelion were demonstrated through in vitro cellular studies. Finally, effective antitumor activity and reduced side effects were confirmed through in vivo antitumor experiments in A549 tumor-bearing nude mice.

Cys.sqlite: A Structured-Information Approach to the Comprehensive Analysis of Cysteine Disulfide Bonds in the Protein Databank

Cysteine is a multifaceted amino acid that is central to the structure and function of many proteins. A disulfide bond formed between two cysteines restrains protein conformations through the strong covalent bond and torsions about the bond that prefer, energetically, ±90°. In this study, we transform over 30 000 Protein Databank files (PDBx/mmCIFs) into a single file, the SQLite database (Cys.sqlite). The database schema is designed to accommodate the structural information on both oxidized and reduced cysteines and to retain essential protein metadata to establish informational and biological provenance. Cys.sqlite contains over 95 000 peptide chains and 500 000 cysteines (700 000 structural conformers); there are over 265 000 cysteine disulfide bond conformations from structures solved with all available experimental methods. The structural information is analyzed with respect to sequence identity cutoff, the experimental method, and energetics of the disulfide. We find that as the experimental information becomes limiting and the influence of modeling becomes more pronounced, the observed average strain increases artificially. The database and analyses presented here can be used to improve the refinement of biological structures from experiments that are known to contain one or more disulfide bonds.

Engineering of Bone- and CD44-Dual-Targeting Redox-Sensitive Liposomes for the Treatment of Orthotopic Osteosarcoma

This study aimed to develop an efficient step-by-step osteosarcoma (OS)-targeting liposome system functionalized with a redox-cleavable, bone- and cluster of differentiation 44 (CD44)-dual-targeting polymer. Furthermore, the effect of coadministration of a tumor-penetrating peptide, internalizing RGD (iRGD), was investigated. First, a bone-targeting moiety, alendronate (ALN), was conjugated with hyaluronic acid (HA), a ligand for CD44. This ALN-HA conjugate was coupled with DSPE-PEG₂₀₀₀-COOH through a bioreducible disulfide linker (-SS-) to obtain a functionalized lipid, ALN-HA-SS-L, to be postinserted into preformed liposomes loaded with doxorubicin (DOX). The roles of ALN, HA, and the redox sensitivity of the ALN-HA-SS-L liposomes (ALN-HA-SS-L-L) in the anti-OS effect were critically evaluated against various reference liposomal formulations (with only ALN, HA, or redox sensitivity). ALN-HA-SS-L-L displayed a zeta potential of -26.07 ± 0.32 mV and selectively disassembled in the presence of a reducing agent, 10 mM glutathione, which can be found in cancer cells. Compared to various reference liposomes, ALN-HA-SS-L-L/DOX had significantly higher cytotoxicity to human OS MG-63 cells alongside high and rapid cellular uptake. In the orthotopic OS nude mouse models, ALN-HA-SS-L-L/DOX showed remarkable tumor growth suppression and prolonged survival time. This result was further improved by the coadministration of iRGD. The antitumor effects of various liposomes were ranked in the same order as the degree of tumor biodistribution shown by in vivo/ex vivo imaging: ALN-HA-SS-L-L coadministered with iRGD > ALN-HA-SS-L-L > HA-SS-L-L > HA-L-L > PEG-L> free drug. ALN-HA-SS-L-L/DOX also reduced the cardiotoxicity of DOX and lung metastases. Overall, this study demonstrated that ALN-HA-SS-L-L/DOX, equipped with bone- and CD44-dual-targeting abilities and redox sensitivity, could be a promising OS-targeted therapy. The efficacy could also be augmented by coadministration of iRGD.

A cupin domain is involved in α-amylase inhibitory activity

Proteinaceous α-amylase inhibitors have specialized activities that make some strong inhibition of α-amylases. New α-amylase inhibitors continue to be discovered so far. A proteinaceous α-amylase inhibitor CL-AI was isolated and identified from chickpea seeds. CL-AI, encoded by Q9SMJ4, was a storage legumin precursor containing one α-chain and one β-chain, and each chain possessed a same conserved cupin domain. Amino acid mutation and deficiency of cupin domain would lead to loss of α-amylase inhibitory activity, indicating that it was essential for inhibitory activity. CL-AI(α + β) in its single stranded state in vivo had inhibitory activity. After it was processed into one α-chain and one β-chain, the two chains were connected to each other via disulfide bond, which would cover the cupin domains and lead to the loss of inhibitory activity. The CL-AI(α + β), α-chain and β-chain could inhibit various α-amylases and delay the seed germination of wheat, rice and maize as well as the growth and development of potato beetle larva. Two cupin proteins, Glycinin G1 in soybean and Glutelinin in rice were also found to have inhibitory activity. Our results indicated that the cupin domain is involved in α-amylase inhibitory activity and the proteins with a cupin domain may be a new kind of proteinaceous α-amylase inhibitor.

Heavy Metal Removal by Bioaccumulation Using Genetically Engineered Microorganisms

Wastewater effluents from mines and metal refineries are often contaminated with heavy metal ions, so they pose hazards to human and environmental health. Conventional technologies to remove heavy metal ions are well-established, but the most popular methods have drawbacks: chemical precipitation generates sludge waste, and activated carbon and ion exchange resins are made from unsustainable non-renewable resources. Using microbial biomass as the platform for heavy metal ion removal is an alternative method. Specifically, bioaccumulation is a natural biological phenomenon where microorganisms use proteins to uptake and sequester metal ions in the intracellular space to utilize in cellular processes (e.g., enzyme catalysis, signaling, stabilizing charges on biomolecules). Recombinant expression of these import-storage systems in genetically engineered microorganisms allows for enhanced uptake and sequestration of heavy metal ions. This has been studied for over two decades for bioremediative applications, but successful translation to industrial-scale processes is virtually non-existent. Meanwhile, demands for metal resources are increasing while discovery rates to supply primary grade ores are not. This review re-thinks how bioaccumulation can be used and proposes that it can be developed for bioextractive applications-the removal and recovery of heavy metal ions for downstream purification and refining, rather than disposal. This review consolidates previously tested import-storage systems into a biochemical framework and highlights efforts to overcome obstacles that limit industrial feasibility, thereby identifying gaps in knowledge and potential avenues of research in bioaccumulation.

Redox-Responsive Nanoparticle-Mediated Systemic RNAi for Effective Cancer Therapy

Biodegradable polymeric nanoparticles (NPs) have demonstrated significant potential to improve the systemic delivery of RNA interference (RNAi) therapeutics, such as small interfering RNA (siRNA), for cancer therapy. However, the slow and inefficient siRNA release inside tumor cells generally observed for most biodegradable polymeric NPs may result in compromised gene silencing efficacy. Herein, a biodegradable and redox-responsive NP platform, composed of a solid poly(disulfide amide) (PDSA)/cationic lipid core and a lipid-poly(ethylene glycol) (lipid-PEG) shell for systemic siRNA delivery to tumor cells, is developed. This newly generated NP platform can efficiently encapsulate siRNA under extracellular environments and can respond to the highly concentrated glutathione (GSH) in the cytoplasm to induce fast intracellular siRNA release. By screening a library of PDSA polymers with different structures and chain lengths, the optimized NP platform shows the unique features of i) long blood circulation, ii) high tumor accumulation, iii) fast GSH-triggered intracellular siRNA release, and iv) exceptionally effective gene silencing. Together with the facile polymer synthesis technique and robust NP formulation enabling scale-up, this new redox-responsive NP platform may become an effective tool for RNAi-based cancer therapy.

Disulfide Connectivity Analysis of Peptides Bearing Two Intramolecular Disulfide Bonds Using MALDI In-Source Decay

Disulfide connectivity in peptides bearing at least two intramolecular disulfide bonds is highly important for the structure and the biological activity of the peptides. In that context, analytical strategies allowing a characterization of the cysteine pairing are of prime interest for chemists, biochemists, and biologists. For that purpose, this study evaluates the potential of MALDI in-source decay (ISD) for characterizing cysteine pairs through the systematic analysis of identical peptides bearing two disulfide bonds, but not the same cysteine connectivity. Three different matrices have been tested in positive and/or in negative mode (1,5-DAN, 2-AB and 2-AA). As MALDI-ISD is known to partially reduce disulfide bonds, the data analysis of this study rests firstly on the deconvolution of the isotope pattern of the parent ions. Moreover, data analysis is also based on the formed fragment ions and their signal intensities. Results from MS/MS-experiments (MALDI-ISD-MS/MS) constitute the last reference for data interpretation. Owing to the combined use of different ISD-promoting matrices, cysteine connectivity identification could be performed on the considered peptides. Graphical Abstract ᅟ.

Redox-sensitive micelles for targeted intracellular delivery and combination chemotherapy of paclitaxel and all-trans-retinoid acid

The application of paclitaxel (PTX) in clinic has been restricted due to its poor solubility. Several traditional nano-medicines have been developed to improve this defect, while they are still lack of tumor targeting ability and rapid drug release. In this work, an amphiphilic polymeric micelle of hyaluronic acid (HA) – all-trans-retinoid acid (ATRA) with a disulfide bond, was developed successfully for the co-delivery of PTX and ATRA. The combination chemotherapy of PTX and ATRA can strengthen the anti-tumor activity. Along with self-assembling to micelles in water, the delivery system displayed satisfying drug loading capacities for both PTX (32.62% ± 1.39%) and ATRA, due to directly using ATRA as the hydrophobic group. Rapid drug release properties of the PTX-loaded redox-sensitive micelles (HA-SS-ATRA) in vitro were confirmed under reducing condition containing GSH. Besides, HA-CD44 mediated endocytosis promoted the uptake of HA-SS-ATRA micelles by B16F10 cells. Due to these properties, cytotoxicity assay verified that PTX-loaded HA-SS-ATRA micelles showed concentration-dependent cytotoxicity and displayed obvious combination therapy of PTX and ATRA. Importantly, HA-SS-ATRA micelles could remarkably prolong plasma circulation time after intravenously administration. Therefore, redox-sensitive HA-SS-ATRA micelles could be utilized and explored as a promising drug delivery system for cancer combination chemotherapy.

l-Serine-modified polyamidoamine dendrimer as a highly potent renal targeting drug carrier

Effective delivery of drug carriers selectively to the kidney is challenging because of their uptake by the reticuloendothelial system in the liver and spleen, which limits effective treatment of kidney diseases and results in side effects. To address this issue, we synthesized l-serine (Ser)-modified polyamidoamine dendrimer (PAMAM) as a potent renal targeting drug carrier. Approximately 82% of the dose was accumulated in the kidney at 3 h after i.v. injection of ¹¹¹In-labeled Ser-PAMAM in mice, while i.v. injection of ¹¹¹In-labeled unmodified PAMAM, l-threonine modified PAMAM, and l-tyrosine modified PAMAM resulted in kidney accumulations of 28%, 35%, and 31%, respectively. Single-photon emission computed tomography/computed tomography (SPECT/CT) images also indicated that ¹¹¹In-labeled Ser-PAMAM specifically accumulated in the kidneys. An intrakidney distribution study showed that fluorescein isothiocyanate-labeled Ser-PAMAM accumulated predominantly in renal proximal tubules. Results of a cellular uptake study of Ser-PAMAM in LLC-PK1 cells in the presence of inhibitors [genistein, 5-(N-ethyl-N-isopropyl)amiloride, and lysozyme] revealed that caveolae-mediated endocytosis, micropinocytosis, and megalin were associated with the renal accumulation of Ser-PAMAM. The efficient renal distribution and angiotensin-converting enzyme (ACE) inhibition effect of captopril (CAP), an ACE inhibitor, was observed after i.v. injection of the Ser-PAMAM-CAP conjugate. These findings indicate that Ser-PAMAM is a promising renal targeting drug carrier for the treatment of kidney diseases. Thus, the results of this study demonstrate efficient renal targeting of a drug carrier via Ser modification.

Redox-Responsive Core-Cross-Linked Block Copolymer Micelles for Overcoming Multidrug Resistance in Cancer Cells

Success of chemotherapy as a treatment for cancer has been often inhibited by multidrug resistance (MDR) of the cancer cells. There is a clear need to generate strategies to overcome this resistance. In this work, we have developed redox-responsive and core-cross-linked micellar nanocarriers using poly(ethylene glycol)-block-poly(2-(methacryloyloxy)ethyl 5-(1,2-dithiolan-3-yl)pentanoate) diblock copolymers (PEG-b-PLAHEMA) with tunable swelling properties for the delivery of drugs toward drug-sensitive MDA-MB-231 and drug-resistant MDA-MB-231 (231R) cancer cells. PEG-b-PLAHEMA containing varying number of 2-(methacryloyloxy)ethyl 5-(1,2-dithiolan-3-yl)pentanoate (LAHEMA) units were synthesized by employing the reversible addition-fragmentation chain transfer polymerization technique. The block copolymer self-assembly, cross-linking induced by reduction, and de-cross-linking triggered time-dependent controlled swelling of micelles were studied using dynamic light scattering, fluorescence spectroscopy, and transmission electron microscopy. In vitro cytotoxicity, cellular uptake efficiency, and glutathione-responsive anticancer activity of doxorubicin (DOX) encapsulated in core-cross-linked block copolymer micelles (CCMs) toward both drug-sensitive and drug-resistant cancer cell lines were evaluated. Significant reduction in IC₅₀ was observed by DOX-loaded CCMs toward drug-resistant 231R cancer cell lines, which was further improved by coencapsulating DOX and verapamil (a P-glycoprotein inhibitor) in CCMs. Thus, these reduction-sensitive biocompatible CCMs with tunable swelling property are very promising in overcoming MDR in cancer cells.

Enhanced Antiglioma Efficacy of Ultrahigh Loading Capacity Paclitaxel Prodrug Conjugate Self-Assembled Targeted Nanoparticles

Glioblastoma multiforme (GBM) presents one of the most lethal brain tumor with a dismal prognosis. And nanodrug delivery system (nano-DDS) have raised a lot of concern, while the conventional nanoformulations addressed many limitations, especially the low drug loading capacity and poor stability in vivo. Herein, we proposed PTX prodrug (PTX-SS-C₁₈) conjugate self-assembled nanoparticles (PSNPs) functionalized with Pep-1, glioma homing peptide, to overcome the blood brain tumor barrier (BBTB) via interleukin 13 receptor α2 (IL-13Rα2)-mediated endocytosis for targeting GMB. This nanocarrier was with ultrahigh drug loading capacity (56.03%) and redox-sensitivity to the up-expression of glutathione in glioma tumors. And compared with PEG-PSNPs, Pep-PSNPs could significantly enhance cellular uptake in U87MG cells via IL-13Rα2-mediated endocytosis. Enhanced cytotoxicity of Pep-PSNPs against U87MG cells and BCEC cells pretreated with glutathione monoester (GSH-OEt) confirmed that this nanosystem was sensitive to reduction environment, and there was significant difference between targeting and nontargeting groups in MTT assay. Real-time fluorescence image of intracranialU87MG glioma-bearing mice revealed that Pep-PSNPs could more efficiently accumulate at tumor site and improve the penetration. Furthermore, the ex vivo fluorescence imaging and corresponding semiquantitative results displayed that the glioma fluorescence intensity of Pep-PSNPs group was 1.74-fold higher than that of nontargeting group. Pep-PSNPs exhibited remarkable antiglioblastoma efficacy with an extended median survival time. In conclusion, Pep-PSNPs had a promising perspective as a targeting drug delivery system of PTX for glioma treatment.

Triple Redox Responsive Poly(Ethylene Glycol)-Polycaprolactone Polymeric Nanocarriers for Fine-Controlled Drug Release

Stimuli-responsive nanocarriers with the ability to respond to tumorous heterogeneity have been extensively developed for drug delivery. However, the premature release during blood circulation and insufficient intracellular drug release are still a significant issue. Herein, three disulfide bonds are introduced into the amphiphilic poly(ethylene glycol)-polycaprolactone copolymer blocks to form triple-sensitive cleavable polymeric nanocarrier (tri-PESC NPs) to improve its sensitivity to narrow glutathione (GSH) concentration. The tri-PESC NPs keep intact during blood circulation due to the limited cleaving of triple-disulfide bonds, whereas the loaded drug is efficiently released at tumor cells with the increased concentration of GSH. In vitro studies of doxorubicin-loaded tri-PESC NPs show that the nanocarriers achieve sufficient drug release in cancerous cells and inhibit the tumor cells growth, though they only bring minimum damage to normal cells. Therefore, the tri-PESC NPs with triple-sensitive cleavable bonds hold great promise to improve the therapeutic index in cancer therapy.

HDX-MS and deletion analysis of the type 4 secretion system protein TraF from the Escherichia coli F plasmid

Conjugative DNA transfer by the F-plasmid is achieved through a type IV secretion system (T4SS) encoded within the plasmid's transfer region; TraF is one of several F-T4SS proteins essential for F-pilus assembly. In order to identify regions of the protein important for TraF function, a series of deletion mutants were assessed for their ability to recover conjugative transfer in a traF knockout. Interestingly, modification of any region of TraF abolishes pilus synthesis, resulting in a loss of rescue of conjugative function. Dynamic analysis of TraF by time-resolved hydrogen-deuterium exchange revealed that the C-terminal region containing the predicted thioredoxin-like domain is quite structured, while the N-terminal region, predicted to interact with TraH in the intact F-T4SS, was more dynamic.

Binding Interactions of Keratin-Based Hair Fiber Extract to Gold, Keratin, and BMP-2

Hair-derived keratin biomaterials composed mostly of reduced keratin proteins (kerateines) have demonstrated their utility as carriers of biologics and drugs for tissue engineering. Electrostatic forces between negatively-charged keratins and biologic macromolecules allow for effective drug retention; attraction to positively-charged growth factors like bone morphogenetic protein 2 (BMP-2) has been used as a strategy for osteoinduction. In this study, the intermolecular surface and bulk interaction properties of kerateines were investigated. Thiol-rich kerateines were chemisorbed onto gold substrates to form an irreversible 2-nm rigid layer for surface plasmon resonance analysis. Kerateine-to-kerateine cohesion was observed in pH-neutral water with an equilibrium dissociation constant (KD) of 1.8 × 10(-4) M, indicating that non-coulombic attractive forces (i.e. hydrophobic and van der Waals) were at work. The association of BMP-2 to kerateine was found to be greater (KD = 1.1 × 10(-7) M), within the range of specific binding. Addition of salts (phosphate-buffered saline; PBS) shortened the Debye length or the electrostatic field influence which weakened the kerateine-BMP-2 binding (KD = 3.2 × 10(-5) M). BMP-2 in bulk kerateine gels provided a limited release in PBS (~ 10% dissociation in 4 weeks), suggesting that electrostatic intermolecular attraction was significant to retain BMP-2 within the keratin matrix. Complete dissociation between kerateine and BMP-2 occurred when the PBS pH was lowered (to 4.5), below the keratin isoelectric point of 5.3. This phenomenon can be attributed to the protonation of keratin at a lower pH, leading to positive-positive repulsion. Therefore, the dynamics of kerateine-BMP-2 binding is highly dependent on pH and salt concentration, as well as on BMP-2 solubility at different pH and molarity. The study findings may contribute to our understanding of the release kinetics of drugs from keratin biomaterials and allow for the development of better, more clinically relevant BMP-2-conjugated systems for bone repair and regeneration.

Genome-Wide Screening Identifies Six Genes That Are Associated with Susceptibility to Escherichia coli Microcin PDI

The microcin PDI inhibits a diverse group of pathogenic Escherichia coli strains. Coculture of a single-gene knockout library (BW25113; n=3,985 mutants) against a microcin PDI-producing strain (E. coli 25) identified six mutants that were not susceptible (ΔatpA, ΔatpF, ΔdsbA, ΔdsbB, ΔompF, and ΔompR). Complementation of these genes restored susceptibility in all cases, and the loss of susceptibility was confirmed through independent gene knockouts in E. coli O157:H7 Sakai. Heterologous expression of E. coli ompF conferred susceptibility to Salmonella enterica and Yersinia enterocolitica strains that are normally unaffected by microcin PDI. The expression of chimeric OmpF and site-directed mutagenesis revealed that the K47G48N49 region within the first extracellular loop of E. coli OmpF is a putative binding site for microcin PDI. OmpR is a transcriptional regulator for ompF, and consequently loss of susceptibility by the ΔompR strain most likely is related to this function. Deletion of AtpA and AtpF, as well as AtpE and AtpH (missed in the original library screen), resulted in the loss of susceptibility to microcin PDI and the loss of ATP synthase function. Coculture of a susceptible strain in the presence of an ATP synthase inhibitor resulted in a loss of susceptibility, confirming that a functional ATP synthase complex is required for microcin PDI activity. In trans expression of ompF in the ΔdsbA and ΔdsbB strains did not restore a susceptible phenotype, indicating that these proteins are probably involved with the formation of disulfide bonds for OmpF or microcin PDI.

Structural dynamics and inhibitor searching for Wnt-4 protein using comparative computational studies

Wnt-4 (wingless mouse mammary tumor virus integration site-4) protein is involved in many crucial embryonic pathways regulating essential processes. Aberrant Wnt-4 activity causes various anomalies leading to gastric, colon, or breast cancer. Wnt-4 is a conserved protein in structure and sequence. All Wnt proteins contain an unusual fold comprising of a thumb (or N-terminal domain) and index finger (or C-terminal domain) bifurcated by a palm domain. The aim of this study was to identify the best inhibitors of Wnt-4 that not only interact with Wnt-4 protein but also with the covalently bound acyl group to inhibit aberrant Wnt-4 activity. A systematic computational approach was used to analyze inhibition of Wnt-4. Palmitoleic acid was docked into Wnt-4 protein, followed by ligand-based virtual screening of nearly 209,847 compounds; conformer generation of 271 compounds resulted from extensive virtual screening and comparative docking of 10,531 conformers of 271 unique compounds through GOLD (Genetic Optimization for Ligand Docking), AutoDock-Vina, and FRED (Fast Rigid Exhaustive Docking) was subsequently performed. Linux scripts was used to handle the libraries of compounds. The best compounds were selected on the basis of having maximum interactions to protein with bound palmitoleic acid. These represented lead inhibitors in further experiments. Palmitoleic acid is important for efficient Wnt activity, but aberrant Wnt-4 expression can be inhibited by designing inhibitors interacting with both protein and palmitoleic acid.

Expression and Characterization of a Recombinant Laccase with Alkalistable and Thermostable Properties from Streptomyces griseorubens JSD-1

Streptomyces griseorubens JSD-1 is a novel actinomycete that could grow efficiently upon lignin, and the ligninolytic genes active in this biotransformation were expected to be crucial. To investigate the molecular mechanism of utilizing lignin, genome sequencing was carried out to obtain its draft genome, which was deposited at GenBank under the accession No. JJMG00000000. Multiple copper oxidase (MCO) was obtained, which proved to be an extracellular enzyme and have relative high expression with the stimulation of ligninolytic materials. Judging from its putative 3D structure, the N-terminal of MCO was bared, which was fit for the linkage of poly-HIS10 tag. As a result, heterogeneous expression conditions of recombinant laccase was achieved with TransB(DE3) grown in a modified terrific broth (TB) medium with an extra addition of 0.5% glucose at 30 °C until optical density at 600 nm (OD600) reached 0.8 when expression was induced by 25 μM isopropyl β-D-1-thiogalactopyranoside (IPTG) and also 100 μM copper sulphate as supplement. Finally, it exhibited special characters of thermal robustness, alkaline activity profiles, high resistance to metallic ions and chemical inhibitors as well as dye decolourization. In summary, our findings illustrated the genetic basic of utilizing lignin in this isolate. Additionally, a novel laccase expected to be potential in agricultural and industrial application was expressed and characterized as well.

Folate-containing reduction-sensitive lipid-polymer hybrid nanoparticles for targeted delivery of doxorubicin

The development and evaluation of folate-targeted and reduction-triggered biodegradable nanoparticles are introduced to the research on targeted delivery of doxorubicin (DOX). This type of folate-targeted lipid-polymer hybrid nanoparticles (FLPNPs) is comprised of a poly(D,L-lactide-co-glycolide) (PLGA) core, a soybean lecithin monolayer, a monomethoxy-poly(ethylene glycol)-S-S-hexadecyl (mPEG-S-S-C16) reduction-sensitive shell, and a folic acid-targeted ligand. FLPNPs exhibited high size stability but fast disassembly in a simulated cancer cell reductive environment. The experiments on the release process in vitro revealed that as a reduction-sensitive drug delivery system, FLPNPs released DOX faster in the presence of 10 mM dithiothreitol (DTT). Results from flow cytometry, confocal image and in vitro cytotoxicity assays revealed that FLPNPs further enhanced cell uptake and generated higher cytotoxicity against human epidermoid carcinoma in the oral cavity than non-targeted redox-sensitive and targeted redox-insensitive controls. Furthermore, in vivo animal experiments demonstrated that systemic administration of DOX-loaded FLPNPs remarkably reduced tumor growth. Experiments on biodistribution of DOX-loaded FLPNPs showed that an increasing amount of DOX accumulated in the tumor. Therefore, FLPNPs formulations have proved to be a stable, controllable and targeted anticancer drug delivery system.

The CydDC Family of Transporters and Their Roles in Oxidase Assembly and Homeostasis

The CydDC complex of Escherichia coli is a heterodimeric ATP-binding cassette type transporter (ABC transporter) that exports the thiol-containing redox-active molecules cysteine and glutathione. These reductants are thought to aid redox homeostasis of the periplasm, permitting correct disulphide folding of periplasmic and secreted proteins. Loss of CydDC results in the periplasm becoming more oxidising and abolishes the assembly of functional bd-type respiratory oxidases that couple the oxidation of ubiquinol to the reduction of oxygen to water. In addition, CydDC-mediated redox control is important for haem ligation during cytochrome c assembly. Given the diverse roles for CydDC in redox homeostasis, respiratory metabolism and the maturation of virulence factors, this ABC transporter is an intriguing system for researchers interested in both the physiology of redox perturbations and the role of low-molecular-weight thiols during infection.

Bioreducible heparin-based nanogel drug delivery system

Bioreducible heparin (HEP)-based nanogels were prepared by derivatizing HEP with vinyl group followed by copolymerizing with cystamine bisacrylamide in aqueous medium in the absence of surfactant. The hydrodynamic diameter of the HEP nanogels could be tuned in the range from 80 to 200 nm. Doxorubicin (DOX) was loaded into the HEP nanogels, and high drug loading content (30%) and efficiency (90%) were achieved. In vitro drug release test revealed that this drug delivery system exhibited strongly redox-sensitive drug release behavior that would greatly favor the in vivo drug delivery performance of the nanogels. After injected into tumor-bearing mice through tail vein, the DOX-loaded HEP nanogels showed remarkable accumulation in tumors as demonstrated by in vivo near infared fluorescence imaging and ex vivo DOX concentration measurements. The doxorubicin accumulation at tumor site goes beyond 9% injected dose per gram of tumor through such delivery system, making that DOX-loaded HEP nanogels have significantly superior in vivo antitumor activity.

Stimuli-responsive polymeric nanoparticles for nanomedicine

Nature continues to be the ultimate in nanotechnology, where polymeric nanometer-scale architectures play a central role in biological systems. Inspired by the way nature forms functional supramolecular assemblies, researchers are trying to make nanostructures and to incorporate these into macrostructures as nature does. Recent advances and progress in nanoscience have demonstrated the great potential that nanomaterials have for applications in healthcare. In the realm of drug delivery, nanomaterials have been used in vivo to protect the drug entity in the systemic circulation, ensuring reproducible absorption of bioactive molecules that do not naturally penetrate biological barriers, restricting drug access to specific target sites. Several building blocks have been used in the formulation of nanoparticles. Thus, stability, drug release, and targeting can be tailored by surface modification. Herein the state of the art of stimuli-responsive polymeric nanoparticles are reviewed. Such systems are able to control drug release by reacting to naturally occurring or external applied stimuli. Special attention is paid to the design and nanoparticle formulation of these so-called smart drug-delivery systems. Future strategies for further developments of a promising controlled drug delivery responsive system are also outlined.

The effect of tensile stress on the conformational free energy landscape of disulfide bonds

Disulfide bridges are no longer considered to merely stabilize protein structure, but are increasingly recognized to play a functional role in many regulatory biomolecular processes. Recent studies have uncovered that the redox activity of native disulfides depends on their C-C-S-S dihedrals, χ2 and χ'2. Moreover, the interplay of chemical reactivity and mechanical stress of disulfide switches has been recently elucidated using force-clamp spectroscopy and computer simulation. The χ2 and χ'2 angles have been found to change from conformations that are open to nucleophilic attack to sterically hindered, so-called closed states upon exerting tensile stress. In view of the growing evidence of the importance of C-C-S-S dihedrals in tuning the reactivity of disulfides, here we present a systematic study of the conformational diversity of disulfides as a function of tensile stress. With the help of force-clamp metadynamics simulations, we show that tensile stress brings about a large stabilization of the closed conformers, thereby giving rise to drastic changes in the conformational free energy landscape of disulfides. Statistical analysis shows that native TDi, DO and interchain Ig protein disulfides prefer open conformations, whereas the intrachain disulfide bridges in Ig proteins favor closed conformations. Correlating mechanical stress with the distance between the two a-carbons of the disulfide moiety reveals that the strain of intrachain Ig protein disulfides corresponds to a mechanical activation of about 100 pN. Such mechanical activation leads to a severalfold increase of the rate of the elementary redox S(N)2 reaction step. All these findings constitute a step forward towards achieving a full understanding of functional disulfides.

Comparative and functional analysis of the widely occurring family of Nep1-like proteins

Nep1-like proteins (NLP) are best known for their cytotoxic activity in dicot plants. NLP are taxonomically widespread among microbes with very different lifestyles. To learn more about this enigmatic protein family, we analyzed more than 500 available NLP protein sequences from fungi, oomycetes, and bacteria. Phylogenetic clustering showed that, besides the previously documented two types, an additional, more divergent, third NLP type could be distinguished. By closely examining the three NLP types, we identified a noncytotoxic subgroup of type 1 NLP (designated type 1a), which have substitutions in amino acids making up a cation-binding pocket that is required for cytotoxicity. Type 2 NLP were found to contain a putative calcium-binding motif, which was shown to be required for cytotoxicity. Members of both type 1 and type 2 NLP were found to possess additional cysteine residues that, based on their predicted proximity, make up potential disulfide bridges that could provide additional stability to these secreted proteins. Type 1 and type 2 NLP, although both cytotoxic to plant cells, differ in their ability to induce necrosis when artificially targeted to different cellular compartments in planta, suggesting they have different mechanisms of cytotoxicity.

Strategies for the production of recombinant protein in Escherichia coli

In the recent past years, a large number of proteins have been expressed in Escherichia coli with high productivity due to rapid development of genetic engineering technologies. There are many hosts used for the production of recombinant protein but the preferred choice is E. coli due to its easier culture, short life cycle, well-known genetics, and easy genetic manipulation. We often face a problem in the expression of foreign genes in E. coli. Soluble recombinant protein is a prerequisite for structural, functional and biochemical studies of a protein. Researchers often face problems producing soluble recombinant proteins for over-expression, mainly the expression and solubility of heterologous proteins. There is no universal strategy to solve these problems but there are a few methods that can improve the level of expression, non-expression, or less expression of the gene of interest in E. coli. This review addresses these issues properly. Five levels of strategies can be used to increase the expression and solubility of over-expressed protein; (1) changing the vector, (2) changing the host, (3) changing the culture parameters of the recombinant host strain, (4) co-expression of other genes and (5) changing the gene sequences, which may help increase expression and the proper folding of desired protein. Here we present the resources available for the expression of a gene in E. coli to get a substantial amount of good quality recombinant protein. The resources include different strains of E. coli, different E. coli expression vectors, different physical and chemical agents and the co expression of chaperone interacting proteins. Perhaps it would be the solutions to such problems that will finally lead to the maturity of the application of recombinant proteins. The proposed solutions to such problems will finally lead to the maturity of the application of recombinant proteins.

A reversible supramolecular assembly containing ionic interactions and disulfide linkages

A reversible ionic supramolecular assembly is described which can be disrupted and reformed by application of either a heating–cooling cycle or a mild redox reaction.