Tyrosine Residues Research Articles

Enzymatically Covalent and Noncovalent Weaving toward Highly Efficient Synthesis of 2D Monolayered Molecular Fabrics.

Molecular fabrics with fascinating physical characteristics, such as structural flexibility and single-layered thinness, have attracted much attention. Chemists worldwide have been working on building unique molecularly woven structures in two dimensions. However, the synthesis of two-dimensional molecular weaving remains a challenging task, especially in water. Herein, we propose a straightforward and practical method to construct 2D molecular fabrics by enzymatically covalent and noncovalent syntheses in water. In particular, aromatic helical pentamers with two-terminal tyrosine residues (Penta-Tyr) can spontaneously dimerize via π-π interactions into double-helical interlocking structure, and the two-terminal tyrosine moieties of Penta-Tyr can undergo oxidative polymerization catalyzed by horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) for effective covalent cross-linking. The 2D monolayered molecular fabrics can be readily prepared by the catalysis of HRP and H2O2 under mild conditions, which exhibit concentration-dependent weaving behavior. This work not only demonstrates an enzyme-catalyzed approach for the highly efficient synthesis of 2D monolayered molecular fabrics for the first time but also will promote the controllable preparation and application of water-soluble 2D molecular fabrics.

Missense mutations of the ephrin receptor EPHA1 associated with Alzheimer's disease disrupt receptor signaling functions.

Missense mutations in the EPHA1 receptor tyrosine kinase have been identified in Alzheimer's patients. To gain insight into their potential role in disease pathogenesis, we investigated the effects of four of these mutations. We show that the P460L mutation in the second fibronectin type III (FN2) domain drastically reduces EPHA1 cell surface localization while increasing tyrosine phosphorylation of the cell surface-localized receptor. The R791H mutation in the kinase domain abolishes EPHA1 tyrosine phosphorylation, indicating abrogation of kinase-dependent signaling. Furthermore, both mutations decrease EPHA1 phosphorylation on S906 in the kinase-SAM linker region, suggesting impairment of a noncanonical form of signaling regulated by serine/threonine kinases. The R492Q mutation, also in the FN2 domain, has milder effects than the P460L mutation while the R926C mutation in the SAM domain increases S906 phosphorylation. We also found that EPHA1 undergoes constitutive proteolytic cleavage in the FN2 domain, generating a soluble 55kDaN-terminal fragment containing the ligand-binding domain and a transmembrane 60kDaC-terminal fragment. The 60kDa WT fragment is phosphorylated on both tyrosine residues and S906, suggesting signaling functions. The P460L mutant 60kDa fragment undergoes proteasomal degradation and the R791H mutant fragment lacks tyrosine phosphorylation and has decreased S906 phosphorylation. These findings advance our understanding of EPHA1 signaling mechanisms and support the notion that alterations in EPHA1 signaling due to missense mutations contribute to Alzheimer's disease pathogenesis.

Therapeutic Insights of Indole Scaffold‐Based Compounds as Protein Kinase Inhibitors

AbstractCancer is deemed to be one of the most severe diseases, which is accountable for the elevated mortality rate after cardiovascular diseases. Despite the huge numbers of drugs that were approved by the USFDA to combat the prevalence of cancer, the resistance of the diverse cancer types to the current medications as well as their high toxicity becomes an obstacle in cancer therapy. Thus, the developing of new medications with improved selectivity and efficiency to cure various types of cancer disease is still an imperative goal. Kinases are phosphorylating enzymes that catalyze the transfer of phosphate from ATP to tyrosine, serine and threonine residues of proteins, which leads to the activation of varied signaling pathways that regulate various cellular functions such as differentiation, proliferation, migration and angiogenesis. Abnormal phosphorylation leads to various diseases such as cancer, overexpression of kinases was frequently observed in different cancerous tissues. Thus, the suppression of the kinase activity has stood out as a strategic pathway for cancer therapy. Otherwise, indole core has displayed as a privileged scaffold with promising anticancer properties and multi‐kinase suppression effect. This review presents various indole‐based anticancer agents as kinase inhibitors in the recent decade. In addition, the various interactions of indole derivatives within the active pocket of different kinases have been highlighted. This review article comprises research reports from 2014 until the present.

Insights into heme degradation and hydrogen peroxide-induced dimerization of human neuroglobin.

In this present study, we investigated the H2O2-induced oligomerization of wild-type human neuroglobin (hNgb) and of some selected variants (C46AC55A, Y44A, Y44F, Y44AC46AC55A, Y44AC46AC55A) to clarify how the process is affected by the Cys46/Cys55 disulfide bond and the distal H-bonding network and to figure out the molecular determinants of the H2O2-induced formation of amyloid-type structures and hNgb aggregates. It turns out that hydrogen peroxide exerts a two-fold effect on hNgb, inducing both heme breakdown and protein dimerization/polymerization. The enhanced resistance to the oxidizing effect of H2O2 of the disulfide-free variants indicates that both effects are strictly influenced by the heme accessibility for H2O2. Most importantly, the H2O2-induced neuroglobin dimerization/polymerization turns out to be triggered by tyrosyl radicals resulting from the oxidizing action of Compound I ([Por•Fe(IV) = O]+). Peptide mapping indicates that the H2O2-induced dimerization/polymerization of hNgb mainly involves Tyr44, which forms covalent bonds with all the other tyrosine residues, with a minor contribution from Tyr88. The presented findings contribute further important pieces of information in the quest of identifying all capabilities of hNgb and ultimately its physiological task.

The R203M and D377Y mutations of the nucleocapsid protein promote SARS-CoV-2 infectivity by impairing RIG-I-mediated antiviral signaling.

The viral protein mutations can modify virus-host interactions during virus evolution, and thus alter the extent of infection or pathogenicity. Studies indicate that nucleocapsid (N) protein of SARS-CoV-2 participates in viral genome assembly, intracellular signal regulation and immune interference. However, its biological function in viral evolution is not well understood. SARS-CoV-2 N protein mutations were analyzed in Delta, Omicron, and original strains. Two mutations with a methionine (M) residue at site 203 and a tyrosine (Y) residue at site 377 of the N protein were found in Delta strain but not in Omicron and original strains, and promoted SARS-CoV-2 infection therein. Those mutations, R203M and D377Y, enhanced the inhibitory impact of N protein on the impairment of RIG-I-mediated antiviral signaling, such as IRF3 phosphorylation and IFN-β activation. The viral RNA-binding activity of N protein was promoted by these mutations, effectively attenuating the recognition and interaction of RIG-I with viral RNA compared to the original or other variants. The R203M/D377Y mutations thus enhanced the suppressive activity of the N protein on RIG-I-mediated interferon induction both in vitro and in vivo, which in turn promoted viral replication. This study helps to understand the variability of SARS-CoV-2 in regulating host immunity.

Raman signatures of type A and B influenza viruses: molecular origin of the "catch and kill" inactivation mechanism mediated by micrometric silicon nitride powder.

A multiomic study of the structural characteristics of type A and B influenza viruses by means of highly spectrally resolved Raman spectroscopy is presented. Three virus strains, A H1N1, A H3N2, and B98, were selected because of their known structural variety and because they have co-circulated with variable relative prevalence within the human population since the re-emergence of the H1N1 subtype in 1977. Raman signatures of protein side chains tyrosine, tryptophan, and histidine revealed unequivocal and consistent differences for pH characteristics at the virion surface, while different conformations of two C-S bond configurations in gauche and trans methionine rotamers provided distinct low-wavenumber fingerprints for different virus lineages/subtypes. Short-term exposure to a few percent fraction of silicon nitride (Si3N4) micrometric powder in an aqueous environment completely inactivated the influenza virions, independent of lineage/subtype dependent characteristics. The molecular-scale details of the inactivation process were studied by Raman spectroscopy and interpreted in terms of a "catch and kill" mechanism, in which the hydrolyzing ceramic surface first attracts virions with high efficiency through electrochemical interactions (mimicking cellular sialic acid) and then "poisons" the viruses by local hydrolytic elution of ammonia and nitrogen radicals. The latter event causes severe damage to the virions' structures, including structural degradation of RNA purines, rotameric scrambling of methionine residues, formation of sulfhydryl and ionized carboxyl groups, and deprotonation/torsional deformation of tyrosine, tryptophan, and histidine residues. This study confirmed the antiviral effectiveness of Si3N4 powder, which is safe to the human body and simply activated by water molecules. Raman spectroscopy was confirmed as a powerful tool in molecular virology, complementary to genomics and unique in providing direct information on virus structures at the molecular scale.

Hydrogen Tunneling and Conformational Motions in Nonadiabatic Proton-Coupled Electron Transfer between Interfacial Tyrosines in Ribonucleotide Reductase.

Ribonucleotide reductase (RNR) is essential for DNA synthesis and repair in all living organisms. The mechanism of E. coli RNR requires long-range radical transport through a proton-coupled electron transfer (PCET) pathway spanning two different protein subunits. Herein, the direct PCET reaction between the interfacial tyrosine residues, Y356 and Y731, is investigated with a vibronically nonadiabatic theory that treats the transferring proton and all electrons quantum mechanically. The input quantities to the PCET rate constant expression are computed with a combination of density functional theory and molecular dynamics simulations. The calculations highlight the importance of hydrogen tunneling in this PCET reaction. Compression of the distance between the proton donor and acceptor oxygen atoms of the interfacial tyrosine residues is essential to facilitate hydrogen tunneling by increasing the overlap between the reactant and product proton vibrational wave functions. This compression occurs by thermal conformational fluctuations of these interfacial tyrosine residues. N733 and R411 are identified as key residues that can hydrogen bond to Y731 and Y356, respectively, and thereby compete with the hydrogen-bonding interaction between Y731 and Y356 required for direct PCET. Understanding the roles of hydrogen tunneling and conformational motions in this interfacial PCET reaction, as well as identifying other residues that may impact the kinetics, is important for targeted protein engineering efforts to modulate RNR activity.

Chemical and temporal manipulation of early steps in protein assembly tunes the structure and intermolecular interactions of protein-based materials.

The Drosophila intrinsically disordered protein Ultrabithorax (Ubx) undergoes a series of phase transitions, beginning with noncovalent interactions between apparently randomly organized monomers, and evolving over time to form increasingly ordered coacervates. This assembly process ends when specific dityrosine covalent bonds lock the monomers in place, forming macroscale materials. Inspired by this hierarchical, multistep assembly process, we analyzed the impact of protein concentration, assembly time, and subphase composition on the early, noncovalent stages of Ubx assembly, which are extremely sensitive to their environment. We discovered that in low salt buffers, we can generate a new type of Ubx material from early coacervates using 5-fold less protein, and 100-fold less assembly time. Comparison of the new materials with standard Ubx fibers also revealed differences in the extent of wrinkling on the fiber surface. A new image analysis technique based on autocorrelation of scanning electron microscopy (SEM) images was developed to quantify these structural differences. These differences extend to the molecular level: new materials form more dityrosine covalent cross-links per monomer, but without requiring the specific tyrosine residues necessary for crosslinking previously established materials. We conclude that varying the assembly conditions represents a facile and inexpensive process for creating new materials. Most new biopolymers are created by changing the composition of the monomers or the method used to drive assembly. In contrast, in this study we used the same monomers and assembly approach, but altered the assembly time and chemical environment to create a new material with unique properties.

Measurements of Iodination in Thyroglobulin: A Step Toward the Next Generation of Thyroid Cancer Monitoring

Abstract Thyroglobulin (Tg) is a 330-kDa homodimeric protein that that is the prohormone of thyroid hormones triiodothyronine (T3) and thyroxine (T4). The most critical steps of thyroid hormone synthesis by Tg are iodination and fusion of specific tyrosine residues that are in close proximity to each other in the folded Tg protein. The degree of Tg iodination has been studied widely to determine if it is correlated with thyroid autoimmune disease with mixed results, but these efforts have been limited by the lack of an effective quantitative technique. Simultaneously, the treatment of thyroid cancer has undergone a shift toward partial thyroidectomies, thus undermining the value of Tg measurements. A possible alternative to established monitoring techniques is measurement of Tg iodination states as it has been shown that tumor-derived Tg has significantly lower iodine content. Such measurements require a thorough understanding of normal iodination status. In this study, state-of-the-art liquid chromatography–tandem mass spectrometry (LC-MS/MS) instrumentation is used to perform bottom-up proteomics experiments and identify iodinated residues within commercially available Tg. Using this technique, sequence coverages greater than 90% were achieved, which resulted in identification of previously identified and novel hormone synthesis and donor sites. Based on the results of these discovery experiments, 5 iodination sites were selected for targeted quantitative LC-MS/MS measurements, which suggested that hormone synthesis occurs predominantly at Y24 and Y2766. The results presented herein lay the foundation for routine measurements of iodinated residues, which has the potential to overcome the limitations of current monitoring techniques and benefit patient care.

Arabidopsis thaliana DNA Damage Response Mutants Challenged with Genotoxic Agents-A Different Experimental Approach to Investigate the TDP1α and TDP1β Genes.

Background/Objectives: DNA damage response (DDR) is a highly conserved and complex signal transduction network required for preserving genome integrity. DNA repair pathways downstream of DDR include the tyrosyl-DNA phosphodiesterase1 (TDP1) enzyme that hydrolyses the phosphodiester bond between the tyrosine residue of topoisomerase I (TopI) and 3'-phosphate end of DNA. A small TDP1 subfamily, composed of TDP1α and TDP1β, is present in plants. The aim of this work was to investigate the role of the two TDP1 genes in the DDR context. Methods: A series of Arabidopsis thaliana DDR single and double mutants defective in the sog1, e2fb, pol2A, atm, and atr genes, treated with the genotoxic agents camptothecin (CPT, inhibitor of TopI) and NSC120686 (NSC, inhibitor of TDP1), were used. These compounds were specifically used due to their known impact on the TDP1 function. The effect of the treatments was assessed via phenotypic analyses that included germination percentage, speed, and seedling growth. Subsequently, the expression of the TDP1α and TDP1β genes was monitored through qRT-PCR. Results: Overall, the gathered data indicate that the atm mutant was highly sensitive to NSC120686, both phenotypically and concerning the TDP1α gene expression profiles. Alternatively, the upregulation of TDP1β in e2fb, pol2a, and atr supports its implication in the replication stress response. Conclusions: The current study demonstrates that genotoxic stress induced by CPT and NSC has a genotype-dependent effect reflected by a differential expression of TDP1 genes and early phenotypic development.

Kinetics of reformation of the S0 state capable of progressing to the S1 state after the O2 release by photosystem II.

The active site for water oxidation in photosystem II (PSII) comprises a Mn4CaO5 cluster adjacent to a redox-active tyrosine residue (TyrZ). During the water-splitting process, the enzyme transitions through five sequential oxidation states (S0 to S4), with O2 evolution occurring during the S3TyrZ· to S0TyrZ transition. Chloride also plays a role in this mechanism. Using PSII from Thermosynechococcus vestitus, where Ca and Cl were replaced with Sr and Br to slow the S3TyrZ· to S0TyrZ + O2 transition (t1/2 ~ 5ms at room temperature), it was observed that the recovery of a S0 state, defined as the state able to progress to S1, exhibits similar kinetics (t1/2 ~ 5ms). This suggests that in CaCl-PSII, the reformation of the functional S0 state directly follows the S3TyrZ· to S0TyrZ + O2 transition, with no additional delay required for the insertion of a new substrate water molecule (O5) and associated protons.

Cross-Species Epitope Sequence Analysis for Discovery of Existing Antibodies Useful for Phospho-Specific Protein Detection in Model Species.

Signaling pathways play key roles in many important biological processes, such as cell division, differentiation, and migration. Phosphorylation site-specific antibodies specifically target proteins phosphorylated on a given tyrosine, threonine, or serine residue. The use of phospho-specific antibodies facilitates the analysis of signaling pathway regulation and activity. Given the usefulness of phospho-specific antibodies, a number of collections of these antibodies have been generated, typically for the detection of phosphorylated mammalian proteins. Anecdotal evidence shows that some of these are also useful for the detection of phosphorylated forms of orthologous proteins in model organisms. We propose that anti-phospho-mammalian protein antibody collections comprise an untapped resource for research in other species. To systematically analyze the potential utility of anti-phospho-mammalian protein antibodies in other species, we developed the Cross-species Epitope Sequence Analysis software tool (CESA). CESA identifies and aligns orthologous proteins in model species and then analyzes the conservation of antibody target sites. We used CESA to predict what phospho-specific antibodies in a collection from Cell Signaling Technology (CST) might be useful for studies in Drosophila melanogaster and other species. CESA predicts that more than 232 sites on 116 Drosophila proteins can potentially be targeted by the antibodies initially developed at CST to detect human, mouse, or rat phosphoproteins.

Research of carrying mechanism between β-lactoglobulin and linoleic acid: Effects on protein structure and oxidative stability of linoleic acid.

Spectroscopic techniques and molecular docking were employed to explore the binding mechanism and structural characteristics of β-lactoglobulin (β-lg) with linoleic acid. The research revealed that the interaction between β-lg and linoleic acid was primarily governed by static quenching. The attachment of linoleic acid to β-lg happened naturally via hydrophobic forces. The interaction between β-lg and linoleic acid had minimal impact on the area surrounding the tryptophan and tyrosine residues in β-lg, and it does not notably change the secondary structure of β-lg. Results of molecular docking and molecular dynamics indicated that linoleic acid binds mainly to the hydrophobic cavity inside β-lg, closer to the tryptophan residues.At the same time the stability of the proteins in the complex was significantly improved compared to the free β-lg. The stability against oxidation and the shelf life of the β-lg/linoleic acid complex were evaluated as well. Compared to free linoleic acid, the complex exhibited lower peroxide and anisidine values, suggesting that its formation with β-lg reduced the creation of primary oxidation products.

Mechanism of ultrafast flavin photoreduction in the active site of flavoenzyme LSD1 histone demethylase.

Photoreduction of oxidized flavins has a functional role in photocatalytic and photoreceptor flavoproteins. In flavoproteins without light-dependent physiological functions, ultrafast, reversible flavin photoreduction is supposedly photoprotective by nature, and holds potential for nonnatural photocatalytic applications. In this work, we combine protein mutagenesis, ultrafast spectroscopy, molecular dynamics simulations and quantum mechanics calculations to investigate the nonfunctional flavin photoreduction in a flavoenzyme, lysine-specific demethylase 1 (LSD1) which is pivotal in DNA transcription. LSD1 harbors an oxidized flavin adenine dinucleotide (FAD) cofactor and multiple electron-donating residues in the active site. Upon photoexcitation, the FAD cofactor is photoreduced in <200 fs by electron transfer (ET) from nearby residue(s), and the charge pairs recombine in ca. 2 ps. Site-directed mutagenesis pinpoints a specific tryptophan residue, W751, as the primary electron donor, whereas a tyrosine residue, Y761, despite being located closer to the flavin ring, does not effectively contribute to the process. Based on a hybrid quantum-classical computational approach, we characterize the W751-FAD and Y761-FAD charge-transfer states (CTW751 and CTY761, respectively), as well as the FAD locally excited state (LEFAD), and demonstrate that the coupling between LEFAD and CTW751 is larger than those involving CTY761 by an order of magnitude, rationalizing the experimental observations. More generally, this work highlights the role of the intrinsic protein environment and details of donor-acceptor molecular configurations on the dynamics of short-range ET involving a flavin cofactor and amino acid residue(s).

Reactivity of a heterobinuclear heme-peroxo-Cu complex with para-substituted catechols shows a pK a-dependent change in mechanism.

In biological systems, heme-copper oxidase (HCO) enzymes play a crucial role in the oxygen reduction reaction (ORR), where the pivotal O-O bond cleavage of the (heme)FeIII-peroxo-CuII intermediate is facilitated by active-site (peroxo core) hydrogen bonding followed by proton-coupled electron transfer (PCET) from a nearby (phenolic) tyrosine residue. A useful approach to comprehend the fundamental relationships among H-bonding/proton/H-atom donors and their abilities to induce O-O bond homolysis involves the investigation of synthetic, bioinspired model systems where the exogenous substrate properties (such as pK a and bond dissociation energy (BDE)) can be systematically altered. This report details the reactivity of a heme-peroxo-copper HCO model complex (LS-4DCHIm) toward a series of substituted catechol substrates that span a range of pK a and O-H bond BDE values, exhibiting different reaction mechanisms. Considering their interactions with the bridging peroxo ligand in LS-4DCHIm, the catechol substrates are importantly capable of one or two (i) H-bonds, (ii) proton transfers, and/or (iii) net H-atom transfers, thereby making them attractive, yet complex candidates for studying the redox chemistry of the metal-bound peroxide. A combination of spectroscopic studies and kinetic analysis implies that the suitable modulation of pK a and O-H bond BDE values of catechols result in either double proton transfer with the release of H2O2 or double PCET resulting in reductive O-O bond rupture. The distinguishing role of substrate properties in directing the mechanism and outcome of O2 protonation/reduction reactions is discussed in terms of designing O2-reduction catalysts based on biological inspiration.

Functional and structural polypharmacology of indazole-based privileged ligands to tackle the undruggability of membrane transporters.

Despite the significant roles of solute carrier (SLC) and ATP-binding cassette (ABC) transporters in human health and disease, most remain poorly characterized as intrinsic and/or xenobiotic ligands are unknown, rendering them as 'undruggable'. Polypharmacology, defined as the simultaneous engagement of multiple targets by a single ligand, offers a promising avenue for discovering novel lead compounds addressing these emerging pharmacological challenges - a major focus in contemporary medicinal chemistry. While common structural motifs among phylogenetically diverse proteins have been proposed to underlie polypharmacology through the concept of 'multitarget binding sites', a comprehensive analysis of these functional and structural aspects from a medicinal chemistry perspective has yet to be undertaken. In our study, we synthesized 65 distinct indazole derivatives and evaluated their activity across a broad biological assessment platform encompassing 17 specific and polyspecific SLC and ABC transporters. Notably, ten indazoles exhibited cross-target activity against challenging transporter targets associated with neurodegeneration (ABCA1), metabolic reprogramming (MCT4), and cancer multidrug resistance (ABCC10). Furthermore, molecular blind docking experiments and advanced binding site analyses revealed, for the first time, conserved binding motifs across monocarboxylate transporters (MCTs), organic anion transporting polypeptides (OATPs), organic cation transporters (OCTs), and ABC transporters, characterized by specific and recurring residues of tyrosine, phenylalanine, serine, and threonine. These findings highlight not only the potential of polypharmacology in drug discovery but also provide insights into the structural underpinnings of ligand binding across membrane transporters.

Epidermal growth factor receptor mutations in breast Cancer: Therapeutic challenges and way forward.

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase (RTK) that is upregulated in aggressive triple-negative breast cancer (TNBC). Ligands such as EGF, TGF-α, epigen, and amphiregulin activate the auto-phosphorylation activity of tyrosine residues on EGFR, which regulates the growth, proliferation, adhesion, migration, and survival of cancer cells. Our prior studies depicted that inhibition of EGFR modulates the chemosensitivity in breast cancer stem cells and, thus, serves as a potent therapeutic target in breast cancer. Small-molecule tyrosine kinase inhibitors (TKIs) and monoclonal antibodies (mAbs) specifically targeting EGFR have been clinically approved for breast cancer treatment. However, intrinsic and acquired resistance generated due to EGFR mutations limits the applications of designed EGFR-TKIs in breast cancer patients. This review highlights the therapeutic approaches, and the challenges encountered in targeting EGFR-specific mutations. It suggests the need to develop more advanced higher-generation inhibitors for use in combinatorial therapy along with chemo-or-immune therapeutics in clinics as a breast cancer treatment strategy against relapse of the disease.

Selective labeling of tyrosine residues in proteins: insights from PTAD labeling and tandem mass spectrometry analysis

Evaluation of the tyrosine labeling reagent PTAD for protein covalent labeling studies using tandem mass spectrometry.

Allosteric Changes Underlie the Outside-In Transmission of Activatory Signals in the TCR.

Rather than being contained in a single polypeptide, and unlike receptor tyrosine kinases, the T cell receptor (TCR) divides its signaling functions among its subunits: TCRα/β bind the extracellular ligand, an antigenic peptide-MHC complex (pMHC), and the CD3 subunits (CD3γ, CD3δ, CD3ε, and CD3ζ) transmit this information to the cytoplasm. How information about the quality of pMHC binding outside is transmitted to the cytoplasm remains a matter of debate. In this review, we compile data generated using a wide variety of experimental systems indicating that TCR engagement by an appropriate pMHC triggers allosteric changes transmitted from the ligand-binding loops in the TCRα and TCRβ subunits to the cytoplasmic tails of the CD3 subunits. We summarize how pMHC and stimulatory antibody binding to TCR ectodomains induces the exposure of a polyproline sequence in the CD3ε cytoplasmic tail for binding to the Nck adapter, the exposure of the RK motif in CD3ε for recruiting the Lck tyrosine kinase, and the induced exposure and phosphorylation of tyrosine residues in all the CD3 cytoplasmic tails. We also review the yet incipient data that help elucidate the structural basis of the Active and Resting conformations of the TCR.

The nuclear sulfenome of Arabidopsis: spotlight on histone acetyltransferase GCN5 regulation through functional thiols.

In aerobic life forms, reactive oxygen species (ROS) are produced by the partial reduction of oxygen during energy-generating metabolic processes. In plants, ROS production increases during periods of both abiotic and biotic stress, severely overloading the antioxidant systems. Hydrogen peroxide (H2O2) plays a central role in cellular redox homeostasis and signaling by oxidising crucial cysteines to sulfenic acid, which is considered a biologically relevant post-translational modification (PTM). Until now, the impact of the nucleus on cellular redox homeostasis has been relatively unexplored. The regulation of histone-modifying enzymes by oxidative PTMs at redox-sensitive cysteine or tyrosine residues is particularly intriguing because it allows the integration of redox signaling mechanisms with chromatin control of transcriptional activity. One of the most extensively studied histone acetyltransferases is the conserved GENERAL CONTROL NONDEPRESSIBLE 5 (GCN5) complex. This study investigated the nuclear sulfenome in Arabidopsis thaliana by expressing a nuclear variant of the Yeast Activation Protein-1 (YAP1) probe and identified 225 potential redox-active proteins undergoing S-sulfenylation. Mass spectrometry analysis further confirmed the S-sulfenylation of GCN5 at cysteines 293, 368, and 400, and their functional significance and impact on the GCN5 protein-protein interaction network were assessed using cysteine-to-serine mutagenesis.