RESUMEN
The multidrug efflux transporter EmrE from Escherichia coli requires anionic residues in the substrate binding pocket for coupling drug transport with the proton motive force. Here, we show how protonation of a single membrane embedded glutamate residue (Glu14) within the homodimer of EmrE modulates the structure and dynamics in an allosteric manner using NMR spectroscopy. The structure of EmrE in the Glu14 protonated state displays a partially occluded conformation that is inaccessible for drug binding by the presence of aromatic residues in the binding pocket. Deprotonation of a single Glu14 residue in one monomer induces an equilibrium shift toward the open state by altering its side chain position and that of a nearby tryptophan residue. This structural change promotes an open conformation that facilitates drug binding through a conformational selection mechanism and increases the binding affinity by approximately 2000-fold. The prevalence of proton-coupled exchange in efflux systems suggests a mechanism that may be shared in other antiporters where acid/base chemistry modulates access of drugs to the substrate binding pocket.
Asunto(s)
Antiportadores , Proteínas de Escherichia coli , Escherichia coli , Proteínas de Escherichia coli/metabolismo , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/genética , Escherichia coli/metabolismo , Escherichia coli/genética , Antiportadores/metabolismo , Antiportadores/química , Antiportadores/genética , Sitios de Unión , Unión Proteica , Protones , Conformación Proteica , Espectroscopía de Resonancia Magnética , Ácido Glutámico/metabolismo , Ácido Glutámico/química , Modelos MolecularesRESUMEN
The RAS-mitogen-activated protein kinase (MAPK) pathway includes KSR, RAF, MEK and the phospho-regulatory sensor 14-3-3. Specific assemblies among these components drive various diseases and likely dictate efficacy for numerous targeted therapies, including allosteric MEK inhibitors (MEKi). However, directly measuring drug interactions on physiological RAS-MAPK complexes in live cells has been inherently challenging to query and therefore remains poorly understood. Here we present a series of NanoBRET-based assays to quantify direct target engagement of MEKi on MEK1 and higher-order MEK1-bound complexes with ARAF, BRAF, CRAF, KSR1 and KSR2 in the presence and absence of 14-3-3 in living cells. We find distinct MEKi preferences among these complexes that can be compiled to generate inhibitor binding profiles. Further, these assays can report on the influence of the pathogenic BRAF-V600E mutant on MEKi binding. Taken together, these approaches can be used as a platform to screen for compounds intended to target specific complexes in the RAS-MAPK cascade.
Asunto(s)
Bioensayo , Proteínas Proto-Oncogénicas B-raf , Proteínas Proto-Oncogénicas B-raf/genética , Sistema de Señalización de MAP Quinasas , Inhibidores de Proteínas Quinasas/farmacologíaRESUMEN
Many types of human cancers are being treated with small molecule ATP-competitive inhibitors targeting the kinase domain of receptor tyrosine kinases. Despite initial successful remission, long-term treatment almost inevitably leads to the emergence of drug resistance mutations at the gatekeeper residue hindering the access of the inhibitor to a hydrophobic pocket at the back of the ATP-binding cleft. In addition to reducing drug efficacy, gatekeeper mutations elevate the intrinsic activity of the tyrosine kinase domain leading to more aggressive types of cancer. However, the mechanism of gain-of-function by gatekeeper mutations is poorly understood. Here, we characterized fibroblast growth factor receptor (FGFR) tyrosine kinases harboring two distinct gatekeeper mutations using kinase activity assays, NMR spectroscopy, bioinformatic analyses, and MD simulations. Our data show that gatekeeper mutations destabilize the autoinhibitory conformation of the DFG motif locally and of the kinase globally, suggesting they impart gain-of-function by facilitating the kinase's ability to populate the active state.
Asunto(s)
Neoplasias , Proteínas Tirosina Quinasas Receptoras , Humanos , Receptores de Factores de Crecimiento de Fibroblastos/genética , Neoplasias/tratamiento farmacológico , Mutación , Adenosina Trifosfato/uso terapéutico , Tirosina , Inhibidores de Proteínas Quinasas/químicaRESUMEN
Fast, high-throughput methods for measuring the level and duration of protective immune responses to SARS-CoV-2 are needed to anticipate the risk of breakthrough infections. Here we report the development of two quantitative PCR assays for SARS-CoV-2-specific T cell activation. The assays are rapid, internally normalized and probe-based: qTACT requires RNA extraction and dqTACT avoids sample preparation steps. Both assays rely on the quantification of CXCL10 messenger RNA, a chemokine whose expression is strongly correlated with activation of antigen-specific T cells. On restimulation of whole-blood cells with SARS-CoV-2 viral antigens, viral-specific T cells secrete IFN-γ, which stimulates monocytes to produce CXCL10. CXCL10 mRNA can thus serve as a proxy to quantify cellular immunity. Our assays may allow large-scale monitoring of the magnitude and duration of functional T cell immunity to SARS-CoV-2, thus helping to prioritize revaccination strategies in vulnerable populations.
Asunto(s)
COVID-19 , SARS-CoV-2 , Humanos , SARS-CoV-2/genética , Inmunidad Celular , Reacción en Cadena de la Polimerasa , Linfocitos TRESUMEN
Pseudokinases often operate through functionally related enzymes and receptors. A prime example is the pseudokinase KSR (Kinase Suppressor of RAS), which can act as both an amplifier and inhibitor of members in the RAS-MAPK (Mitogen Activated Protein Kinase) signaling pathway. KSR is structurally related to the active RAF kinases over multiple domains; moreover, the pseudokinase domain of KSR forms physical and regulatory complexes with both RAF and MEK through distinct interfaces. Characterization of small molecule interactions on KSR has been used to uncover novel chemical tools and understand the mechanism of action of clinical drugs. Here, we elaborate on assays and structural methods for measuring binding at orthosteric and interfacial binding sites on KSR. These distinct small molecule pockets provide therapeutic paths for targeting KSR1 and KSR2 pseudokinases in disease, including in RAS and RAF mutant cancers.
Asunto(s)
Proteínas Quinasas , Proteínas Serina-Treonina Quinasas , Sitios de Unión , Conformación Molecular , Fosforilación , Proteínas Quinasas/química , Proteínas Proto-Oncogénicas c-raf/metabolismo , Transducción de SeñalRESUMEN
A novel clinical assay for the detection and quantitation of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was adapted from an in-house, research-based enzyme-linked immunosorbent assay (ELISA). Development and validation were performed under regulatory guidelines, and the test obtained emergency use authorization (EUA) from the New York State Department of Health (NYSDOH) and the Food and Drug Administration (FDA). The Mount Sinai coronavirus disease 2019 (COVID-19) antibody assay is an orthogonal, quantitative direct ELISA test which detects antibodies reactive to the receptor binding domain (RBD) and the spike protein of the novel SARS-CoV-2. The assay is performed on 96-well plates coated with either SARS-CoV-2 recombinant RBD or spike proteins. The test is divided into two stages, a qualitative screening assay against RBD and a quantitative assay against the full-length spike protein. The test uses pooled high titer serum as a reference standard. Negative pre-COVID-19 and positive post-COVID-19, PCR-confirmed specimens were incorporated in each ELISA test run, and the assays were performed independently at two different locations. The Mount Sinai COVID-19 serology performed with high sensitivity and specificity, 92.5% (95% CI: 0.785-0.980) and 100% (CI: 0.939-1.000) respectively. Between-run precision was assessed with a single run repeated over 22 days; and within-run precision was assessed with 10 replicates per day over 22 days. Both were within reported acceptance criteria (CV ≤ 20%). This population-based study reveals the applicability and reliability of this novel orthogonal COVID-19 serology test for the detection and quantitation of antibodies against SARS-CoV-2, allowing a broad set of clinical applications, including the broad evaluation of SARS-CoV-2 seroprevalence and antibody profiling in different population subsets.
RESUMEN
The MAPK/ERK kinase MEK is a shared effector of the frequent cancer drivers KRAS and BRAF that has long been pursued as a drug target in oncology1, and more recently in immunotherapy2,3 and ageing4. However, many MEK inhibitors are limited owing to on-target toxicities5-7 and drug resistance8-10. Accordingly, a molecular understanding of the structure and function of MEK within physiological complexes could provide a template for the design of safer and more effective therapies. Here we report X-ray crystal structures of MEK bound to the scaffold KSR (kinase suppressor of RAS) with various MEK inhibitors, including the clinical drug trametinib. The structures reveal an unexpected mode of binding in which trametinib directly engages KSR at the MEK interface. In the bound complex, KSR remodels the prototypical allosteric pocket of the MEK inhibitor, thereby affecting binding and kinetics, including the drug-residence time. Moreover, trametinib binds KSR-MEK but disrupts the related RAF-MEK complex through a mechanism that exploits evolutionarily conserved interface residues that distinguish these sub-complexes. On the basis of these insights, we created trametiglue, which limits adaptive resistance to MEK inhibition by enhancing interfacial binding. Our results reveal the plasticity of an interface pocket within MEK sub-complexes and have implications for the design of next-generation drugs that target the RAS pathway.
Asunto(s)
Quinasas de Proteína Quinasa Activadas por Mitógenos/química , Quinasas de Proteína Quinasa Activadas por Mitógenos/metabolismo , Proteínas Quinasas/química , Proteínas Quinasas/metabolismo , Piridonas/química , Piridonas/farmacología , Pirimidinonas/química , Pirimidinonas/farmacología , Secuencia de Aminoácidos , Animales , Sitios de Unión/efectos de los fármacos , Humanos , Ratones , Quinasas de Proteína Quinasa Activadas por Mitógenos/antagonistas & inhibidores , Modelos Moleculares , Unión Proteica/efectos de los fármacos , Inhibidores de Proteínas Quinasas/química , Inhibidores de Proteínas Quinasas/farmacología , Especificidad por Sustrato , Quinasas raf/química , Quinasas raf/metabolismoRESUMEN
In this issue of Cell Chemical Biology, Pisa et al. (2020) find that haploid and diploid cells differentially develop resistance to the CENP-E inhibitor GSK923295. The results highlight the power of tumor cells to evade growth inhibition and potentially inform the design of next-generation CENP-E drugs to overcome resistance.
Asunto(s)
Diploidia , Neoplasias , Compuestos Bicíclicos Heterocíclicos con Puentes , Resistencia a Medicamentos , Haploidia , HumanosRESUMEN
A long-standing mystery shrouds the mechanism by which catalytically repressed receptor tyrosine kinase domains accomplish transphosphorylation of activation loop (A-loop) tyrosines. Here we show that this reaction proceeds via an asymmetric complex that is thermodynamically disadvantaged because of an electrostatic repulsion between enzyme and substrate kinases. Under physiological conditions, the energetic gain resulting from ligand-induced dimerization of extracellular domains overcomes this opposing clash, stabilizing the A-loop-transphosphorylating dimer. A unique pathogenic fibroblast growth factor receptor gain-of-function mutation promotes formation of the complex responsible for phosphorylation of A-loop tyrosines by eliminating this repulsive force. We show that asymmetric complex formation induces a more phosphorylatable A-loop conformation in the substrate kinase, which in turn promotes the active state of the enzyme kinase. This explains how quantitative differences in the stability of ligand-induced extracellular dimerization promotes formation of the intracellular A-loop-transphosphorylating asymmetric complex to varying extents, thereby modulating intracellular kinase activity and signaling intensity.
Asunto(s)
Dominio AAA/fisiología , Proteínas Tirosina Quinasas/metabolismo , Proteínas Tirosina Quinasas Receptoras/metabolismo , Dominio AAA/genética , Dominio Catalítico , Dimerización , Activación Enzimática , Humanos , Ligandos , Fosforilación , Unión Proteica , Conformación Proteica , Proteínas Tirosina Quinasas/fisiología , Proteínas Tirosina Quinasas Receptoras/genética , Proteínas Tirosina Quinasas Receptoras/fisiología , Receptor Tipo 1 de Factor de Crecimiento de Fibroblastos/genética , Receptor Tipo 1 de Factor de Crecimiento de Fibroblastos/metabolismo , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/genética , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/metabolismo , Receptor Tipo 3 de Factor de Crecimiento de Fibroblastos/genética , Receptor Tipo 3 de Factor de Crecimiento de Fibroblastos/metabolismo , Transducción de Señal , Relación Estructura-Actividad , Tirosina/químicaRESUMEN
Design of undergraduate laboratory courses that provide meaningful research-based experiences enhance undergraduate curricula and prepare future graduate students for research careers. In this article, a Course-based Undergraduate Research Experience (CURE) laboratory module was designed for upper-division undergraduate biochemistry and chemistry students. The laboratory module enabled students to build upon recently published data in the literature to decipher atomistic insight for an essential protein-protein interaction in human biology through the use of biomolecular NMR spectroscopy. Students compared their results with published data with the goal of identifying specific regions of the protein-protein interaction responsible for triggering an allosteric conformational change. The laboratory module introduced students to basic and advance laboratory techniques, including protein purification, NMR spectroscopy, and analysis of protein structure using molecular visualization software.
RESUMEN
An autoinhibitory network of hydrogen bonds located at the kinase hinge (referred to as the "molecular brake") regulates the activity of several receptor tyrosine kinases. The mechanism whereby mutational disengagement of the brake allosterically activates the kinase in human disease is incompletely understood. We used a combination of NMR, bioinformatics, and molecular dynamics simulation to show that mutational disruption of the molecular brake triggers localized conformational perturbations that propagate to the active site. This entails changes in interactions of an isoleucine, one of three hydrophobic residues that lock the phenylalanine of the DFG motif in an inactive conformation. Structural analysis of tyrosine kinases provides evidence that this allosteric control mechanism is shared across the tyrosine kinase family. We also show that highly activating mutations at the brake diminish the enzyme's thermostability, thereby explaining why these mutations cause milder skeletal syndromes compared with less-activating mutations in the activation loop.
Asunto(s)
Isoleucina/genética , Mutación , Proteínas Tirosina Quinasas/química , Regulación Alostérica , Dominio Catalítico , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Espectroscopía de Resonancia Magnética , Simulación de Dinámica Molecular , Conformación Proteica , Proteínas Tirosina Quinasas/genéticaRESUMEN
Vitally important for controlling gene expression in eukaryotes and prokaryotes, the deprotection of mRNA 5' termini is governed by enzymes whose activity is modulated by interactions with ancillary factors. In Escherichia coli, 5'-end-dependent mRNA degradation begins with the generation of monophosphorylated 5' termini by the RNA pyrophosphohydrolase RppH, which can be stimulated by DapF, a diaminopimelate epimerase involved in amino acid and cell wall biosynthesis. We have determined crystal structures of RppH-DapF complexes and measured rates of RNA deprotection. These studies show that DapF potentiates RppH activity in two ways, depending on the nature of the substrate. Its stimulatory effect on the reactivity of diphosphorylated RNAs, the predominant natural substrates of RppH, requires a substrate long enough to reach DapF in the complex, while the enhanced reactivity of triphosphorylated RNAs appears to involve DapF-induced changes in RppH itself and likewise increases with substrate length. This study provides a basis for understanding the intricate relationship between cellular metabolism and mRNA decay and reveals striking parallels with the stimulation of decapping activity in eukaryotes.
Asunto(s)
Ácido Anhídrido Hidrolasas/química , Ácido Anhídrido Hidrolasas/metabolismo , Isomerasas de Aminoácido/química , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , ARN Mensajero/metabolismo , Regulación Alostérica , Isomerasas de Aminoácido/metabolismo , Cinética , Modelos Moleculares , Unión Proteica , Multimerización de ProteínaRESUMEN
Exchange between conformational states is required for biomolecular catalysis, allostery, and folding. A variety of NMR experiments have been developed to quantify motional regimes ranging from nanoseconds to seconds. In this work, we describe an approach to speed up the acquisition of chemical exchange saturation transfer (CEST) experiments that are commonly used to probe millisecond to second conformational exchange in proteins and nucleic acids. The standard approach is to obtain CEST datasets through the acquisition of a series of 2D correlation spectra where each experiment utilizes a single saturation frequency to 1H, 15N or 13C. These pseudo 3D datasets are time consuming to collect and are further lengthened by reduced signal to noise stemming from the long saturation pulse. In this article, we show how usage of a multiple frequency saturation pulse (i.e., MF-CEST) changes the nature of data collection from series to parallel, and thus decreases the total acquisition time by an integer factor corresponding to the number of frequencies in the pulse. We demonstrate the applicability of MF-CEST on a Src homology 2 (SH2) domain from phospholipase Cγ and the secondary active transport protein EmrE as model systems by collecting 13C methyl and 15N backbone datasets. MF-CEST can also be extended to additional sites within proteins and nucleic acids. The only notable drawback of MF-CEST as applied to backbone 15N experiments occurs when a large chemical shift difference between the major and minor populations is present (typically greater than ~ 8 ppm). In these cases, ambiguity may arise between the chemical shift of the minor population and the multiple frequency saturation pulse. Nevertheless, this drawback does not occur for methyl group MF-CEST experiments or in cases where somewhat smaller chemical shift differences occur are present.
Asunto(s)
Simulación de Dinámica Molecular , Resonancia Magnética Nuclear Biomolecular/métodos , Proteínas/química , Conformación Molecular , Movimiento (Física) , Fosfolipasa C gamma/química , Factores de Tiempo , Dominios Homologos srcRESUMEN
Receptor tyrosine kinase (RTK) signaling is tightly regulated by protein allostery within the intracellular tyrosine kinase domains. Yet the molecular determinants of allosteric connectivity in tyrosine kinase domain are incompletely understood. By means of structural (X-ray and NMR) and functional characterization of pathogenic gain-of-function mutations affecting the FGF receptor (FGFR) tyrosine kinase domain, we elucidated a long-distance allosteric network composed of four interconnected sites termed the 'molecular brake', 'DFG latch', 'A-loop plug', and 'αC tether'. The first three sites repress the kinase from adopting an active conformation, whereas the αC tether promotes the active conformation. The skewed design of this four-site allosteric network imposes tight autoinhibition and accounts for the incomplete mimicry of the activated conformation by pathogenic mutations targeting a single site. Based on the structural similarity shared among RTKs, we propose that this allosteric model for FGFR kinases is applicable to other RTKs.
Asunto(s)
Regulación Alostérica , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/química , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/metabolismo , Cristalografía por Rayos X , Humanos , Espectroscopía de Resonancia Magnética , Proteínas Mutantes/química , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Conformación Proteica , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/genéticaRESUMEN
The molecular basis by which receptor tyrosine kinases (RTKs) recruit and phosphorylate Src Homology 2 (SH2) domain-containing substrates has remained elusive. We used X-ray crystallography, NMR spectroscopy, and cell-based assays to demonstrate that recruitment and phosphorylation of Phospholipase Cγ (PLCγ), a prototypical SH2 containing substrate, by FGF receptors (FGFR) entails formation of an allosteric 2:1 FGFR-PLCγ complex. We show that the engagement of pTyr-binding pocket of the cSH2 domain of PLCγ by the phosphorylated tail of an FGFR kinase induces a conformational change at the region past the cSH2 core domain encompassing Tyr-771 and Tyr-783 to facilitate the binding/phosphorylation of these tyrosines by another FGFR kinase in trans. Our data overturn the current paradigm that recruitment and phosphorylation of substrates are carried out by the same RTK monomer in cis and disclose an obligatory role for receptor dimerization in substrate phosphorylation in addition to its canonical role in kinase activation.
Asunto(s)
Fosfolipasa C gamma/metabolismo , Receptor Tipo 1 de Factor de Crecimiento de Fibroblastos/metabolismo , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/metabolismo , Secuencia de Aminoácidos , Sitios de Unión , Cristalografía por Rayos X , Receptores ErbB/metabolismo , Células HEK293 , Humanos , Hidrólisis , Modelos Moleculares , Datos de Secuencia Molecular , Complejos Multienzimáticos , Resonancia Magnética Nuclear Biomolecular , Fosfatidilinositoles/metabolismo , Fosfolipasa C gamma/química , Fosfolipasa C gamma/genética , Fosforilación , Unión Proteica , Conformación Proteica , Transporte de Proteínas , Receptor Tipo 1 de Factor de Crecimiento de Fibroblastos/química , Receptor Tipo 1 de Factor de Crecimiento de Fibroblastos/genética , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/química , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/genética , Receptores del Factor de Crecimiento Derivado de Plaquetas/metabolismo , Relación Estructura-Actividad , Transfección , Receptor 2 de Factores de Crecimiento Endotelial Vascular/metabolismo , Dominios Homologos srcRESUMEN
The neutral amino acid transporter alanine-serine-cysteine transporter 2 (ASCT2) belongs to the solute carrier 1 (SLC1) family of solute transporters and transports small, neutral amino acids across the membrane, including the physiologically important and ubiquitous amino acid glutamine. Our understanding of the involvement of ASCT2 in the physiological processes involving glutamine is hampered by a lack of understanding of its pharmacology and the absence of high-affinity inhibitors. In this study, we combined an in silico docking approach with experimental investigation of binding parameters to develop new ASCT2 inhibitors and substrates, a series of serine esters, and to determine structural parameters that govern their functional effects. The series of compounds was synthesized using standard methods and exhibited a range of properties, from inhibitors to partial substrates and full substrates. Our results suggest that amino acid derivatives with small side-chain volume and low side-chain hydrophobicity interact strongly with the closed-loop form of the binding site, in which re-entrant loop 2, the presumed extracellular gate for the substrate binding site, is closed off. However, these derivatives bind weakly to the open-loop form (external gate open to the extracellular side), acting as transported substrates. In contrast, inhibitors bind preferentially to the open-loop form. An aromatic residue in the side chain is required for high-affinity interaction. One of the compounds, the l-serine ester serine biphenyl-4-carboxylate reversibly inhibits ASCT2 function with an apparent affinity of 30 µM.