RESUMO
P-type ATPases are found in all kingdoms of life and constitute a wide range of cation transporters, primarily for H+, Na+, K+, Ca2+, and transition metal ions such as Cu(I), Zn(II), and Cd(II). They have been studied through a wide range of techniques, and research has gained very significant insight on their transport mechanism and regulation. Here, we review the structure, function, and dynamics of P2-ATPases including Ca2+-ATPases and Na,K-ATPase. We highlight mechanisms of functional transitions that are associated with ion exchange on either side of the membrane and how the functional cycle is regulated by interaction partners, autoregulatory domains, and off-cycle states. Finally, we discuss future perspectives based on emerging techniques and insights.
Assuntos
Trifosfato de Adenosina/química , ATPases Transportadoras de Cobre/química , ATPase Trocadora de Hidrogênio-Potássio/química , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/química , ATPase Trocadora de Sódio-Potássio/química , Trifosfato de Adenosina/metabolismo , Animais , Sítios de Ligação , Cátions Bivalentes , Cátions Monovalentes , ATPases Transportadoras de Cobre/genética , ATPases Transportadoras de Cobre/metabolismo , ATPase Trocadora de Hidrogênio-Potássio/genética , ATPase Trocadora de Hidrogênio-Potássio/metabolismo , Humanos , Transporte de Íons , Modelos Moleculares , Ligação Proteica , Domínios e Motivos de Interação entre Proteínas , Estrutura Secundária de Proteína , Prótons , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/genética , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/metabolismo , Imagem Individual de Molécula , ATPase Trocadora de Sódio-Potássio/genética , ATPase Trocadora de Sódio-Potássio/metabolismo , Especificidade por SubstratoRESUMO
The brain is highly sensitive to damage caused by infection and inflammation1,2. Herpes simplex virus 1 (HSV-1) is a neurotropic virus and the cause of herpes simplex encephalitis3. It is unknown whether neuron-specific antiviral factors control virus replication to prevent infection and excessive inflammatory responses, hence protecting the brain. Here we identify TMEFF1 as an HSV-1 restriction factor using genome-wide CRISPR screening. TMEFF1 is expressed specifically in neurons of the central nervous system and is not regulated by type I interferon, the best-known innate antiviral system controlling virus infections. Depletion of TMEFF1 in stem-cell-derived human neurons led to elevated viral replication and neuronal death following HSV-1 infection. TMEFF1 blocked the HSV-1 replication cycle at the level of viral entry through interactions with nectin-1 and non-muscle myosin heavy chains IIA and IIB, which are core proteins in virus-cell binding and virus-cell fusion, respectively4-6. Notably, Tmeff1-/- mice exhibited increased susceptibility to HSV-1 infection in the brain but not in the periphery. Within the brain, elevated viral load was observed specifically in neurons. Our study identifies TMEFF1 as a neuron-specific restriction factor essential for prevention of HSV-1 replication in the central nervous system.
Assuntos
Fatores de Restrição Antivirais , Encéfalo , Herpes Simples , Herpesvirus Humano 1 , Proteínas de Membrana , Neurônios , Internalização do Vírus , Replicação Viral , Animais , Feminino , Humanos , Masculino , Camundongos , Fatores de Restrição Antivirais/metabolismo , Encéfalo/citologia , Encéfalo/metabolismo , Encéfalo/patologia , Encéfalo/virologia , Morte Celular , Sistemas CRISPR-Cas/genética , Herpes Simples/imunologia , Herpes Simples/metabolismo , Herpes Simples/virologia , Herpesvirus Humano 1/crescimento & desenvolvimento , Herpesvirus Humano 1/imunologia , Herpesvirus Humano 1/fisiologia , Proteínas de Membrana/metabolismo , Proteínas de Membrana/deficiência , Proteínas de Membrana/genética , Neurônios/virologia , Neurônios/metabolismo , Carga Viral , Nectinas/metabolismo , Miosina não Muscular Tipo IIA/metabolismo , Miosina não Muscular Tipo IIB/metabolismo , Interferon Tipo I , Doenças Neuroinflamatórias/imunologia , Doenças Neuroinflamatórias/metabolismo , Doenças Neuroinflamatórias/patologia , Doenças Neuroinflamatórias/prevenção & controle , Doenças Neuroinflamatórias/virologiaRESUMO
Alpha-synuclein (aSN) is a membrane-associated and intrinsically disordered protein, well known for pathological aggregation in neurodegeneration. However, the physiological function of aSN is disputed. Pull-down experiments have pointed to plasma membrane Ca2+ -ATPase (PMCA) as a potential interaction partner. From proximity ligation assays, we find that aSN and PMCA colocalize at neuronal synapses, and we show that calcium expulsion is activated by aSN and PMCA. We further show that soluble, monomeric aSN activates PMCA at par with calmodulin, but independent of the autoinhibitory domain of PMCA, and highly dependent on acidic phospholipids and membrane-anchoring properties of aSN. On PMCA, the key site is mapped to the acidic lipid-binding site, located within a disordered PMCA-specific loop connecting the cytosolic A domain and transmembrane segment 3. Our studies point toward a novel physiological role of monomeric aSN as a stimulator of calcium clearance in neurons through activation of PMCA.
Assuntos
Cálcio , alfa-Sinucleína , Cálcio/metabolismo , alfa-Sinucleína/genética , alfa-Sinucleína/metabolismo , ATPases Transportadoras de Cálcio da Membrana Plasmática/genética , ATPases Transportadoras de Cálcio da Membrana Plasmática/química , ATPases Transportadoras de Cálcio da Membrana Plasmática/metabolismo , Membrana Celular/metabolismo , Adenosina Trifosfatases/metabolismo , Sítios de LigaçãoRESUMO
The human glycine transporter 1 (GlyT1) regulates glycine-mediated neuronal excitation and inhibition through the sodium- and chloride-dependent reuptake of glycine1-3. Inhibition of GlyT1 prolongs neurotransmitter signalling, and has long been a key strategy in the development of therapies for a broad range of disorders of the central nervous system, including schizophrenia and cognitive impairments4. Here, using a synthetic single-domain antibody (sybody) and serial synchrotron crystallography, we have determined the structure of GlyT1 in complex with a benzoylpiperazine chemotype inhibitor at 3.4 Å resolution. We find that the inhibitor locks GlyT1 in an inward-open conformation and binds at the intracellular gate of the release pathway, overlapping with the glycine-release site. The inhibitor is likely to reach GlyT1 from the cytoplasmic leaflet of the plasma membrane. Our results define the mechanism of inhibition and enable the rational design of new, clinically efficacious GlyT1 inhibitors.
Assuntos
Proteínas da Membrana Plasmática de Transporte de Glicina/antagonistas & inibidores , Proteínas da Membrana Plasmática de Transporte de Glicina/química , Glicina/metabolismo , Sítios de Ligação , Transporte Biológico/efeitos dos fármacos , Cristalografia , Humanos , Modelos Moleculares , Piperazinas/química , Piperazinas/farmacologia , Ligação Proteica , Conformação Proteica , Estabilidade Proteica , Anticorpos de Domínio Único , Sulfonas/química , Sulfonas/farmacologia , SíncrotronsRESUMO
The sodium-potassium-chloride transporter NKCC1 of the SLC12 family performs Na+ -dependent Cl- - and K+ -ion uptake across plasma membranes. NKCC1 is important for regulating cell volume, hearing, blood pressure, and regulation of hyperpolarizing GABAergic and glycinergic signaling in the central nervous system. Here, we present a 2.6 Å resolution cryo-electron microscopy structure of human NKCC1 in the substrate-loaded (Na+ , K+ , and 2 Cl- ) and occluded, inward-facing state that has also been observed for the SLC6-type transporters MhsT and LeuT. Cl- binding at the Cl1 site together with the nearby K+ ion provides a crucial bridge between the LeuT-fold scaffold and bundle domains. Cl- -ion binding at the Cl2 site seems to undertake a structural role similar to conserved glutamate of SLC6 transporters and may allow for Cl- -sensitive regulation of transport. Supported by functional studies in mammalian cells and computational simulations, we describe a putative Na+ release pathway along transmembrane helix 5 coupled to the Cl2 site. The results provide insight into the structure-function relationship of NKCC1 with broader implications for other SLC12 family members.
Assuntos
Potássio , Sódio , Membro 2 da Família 12 de Carreador de Soluto , Humanos , Microscopia Crioeletrônica , Potássio/metabolismo , Sódio/metabolismo , Membro 2 da Família 12 de Carreador de Soluto/genética , Membro 2 da Família 12 de Carreador de Soluto/químicaRESUMO
The ability to regulate transmembrane ion transport in response to various cues is vital to any living cell. In neurons, one key example of critical ion control relates to the extrusion of chloride mediated by the potassium-chloride-cotransporters (KCC1-4). In a recent hallmark study, Chi etâ£al (2021) report cryo-EM structures of human KCC1 and KCC3b, delineating in detail how regulation by phosphorylation inhibits the transport activity. The authors also identify a stabilizing binding site for nucleotides and speculate on its functional role.
Assuntos
Simportadores , Sítios de Ligação , Cloretos/metabolismo , Humanos , Fosforilação , Domínios Proteicos , Simportadores/genética , Simportadores/metabolismoRESUMO
MhsT of Bacillus halodurans is a transporter of hydrophobic amino acids and a homologue of the eukaryotic SLC6 family of Na+ -dependent symporters for amino acids, neurotransmitters, osmolytes, or creatine. The broad range of transported amino acids by MhsT prompted the investigation of the substrate recognition mechanism. Here, we report six new substrate-bound structures of MhsT, which, in conjunction with functional studies, reveal how the flexibility of a Gly-Met-Gly (GMG) motif in the unwound region of transmembrane segment 6 (TM6) is central for the recognition of substrates of different size by tailoring the binding site shape and volume. MhsT mutants, harboring substitutions within the unwound GMG loop and substrate binding pocket that mimick the binding sites of eukaryotic SLC6A18/B0AT3 and SLC6A19/B0AT1 transporters of neutral amino acids, exhibited impaired transport of aromatic amino acids that require a large binding site volume. Conservation of a general (G/A/C)ΦG motif among eukaryotic members of SLC6 family suggests a role for this loop in a common mechanism for substrate recognition and translocation by SLC6 transporters of broad substrate specificity.
Assuntos
Sistemas de Transporte de Aminoácidos/metabolismo , Aminoácidos/metabolismo , Proteínas de Bactérias/metabolismo , Proteínas de Membrana/metabolismo , Bacillus/metabolismo , Sítios de Ligação/fisiologia , Conformação Proteica , Especificidade por Substrato/fisiologiaRESUMO
Type 4 P-type ATPases (P4-ATPases) are lipid flippases that drive the active transport of phospholipids from exoplasmic or luminal leaflets to cytosolic leaflets of eukaryotic membranes. The molecular architecture of P4-ATPases and the mechanism through which they recognize and transport lipids have remained unknown. Here we describe the cryo-electron microscopy structure of the P4-ATPase Drs2p-Cdc50p, a Saccharomyces cerevisiae lipid flippase that is specific to phosphatidylserine and phosphatidylethanolamine. Drs2p-Cdc50p is autoinhibited by the C-terminal tail of Drs2p, and activated by the lipid phosphatidylinositol-4-phosphate (PtdIns4P or PI4P). We present three structures that represent the complex in an autoinhibited, an intermediate and a fully activated state. The analysis highlights specific features of P4-ATPases and reveals sites of autoinhibition and PI4P-dependent activation. We also observe a putative lipid translocation pathway in this flippase that involves a conserved PISL motif in transmembrane segment 4 and polar residues of transmembrane segments 2 and 5, in particular Lys1018, in the centre of the lipid bilayer.
Assuntos
ATPases Transportadoras de Cálcio/química , ATPases Transportadoras de Cálcio/metabolismo , Microscopia Crioeletrônica , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/enzimologia , Sítios de Ligação , Transporte Biológico , ATPases Transportadoras de Cálcio/antagonistas & inibidores , ATPases Transportadoras de Cálcio/ultraestrutura , Ativação Enzimática , Bicamadas Lipídicas/metabolismo , Modelos Biológicos , Modelos Moleculares , Fosfatidiletanolaminas/metabolismo , Fosfatos de Fosfatidilinositol/química , Fosfatos de Fosfatidilinositol/metabolismo , Fosfatidilserinas/metabolismo , Domínios Proteicos , Proteínas de Saccharomyces cerevisiae/antagonistas & inibidores , Proteínas de Saccharomyces cerevisiae/ultraestruturaRESUMO
The regulation of dopamine (DA) removal from the synaptic cleft is a crucial process in neurotransmission and is facilitated by the sodium- and chloride-coupled dopamine transporter DAT. Psychostimulant drugs, cocaine, and amphetamine, both block the uptake of DA, while amphetamine also triggers the release of DA. As a result, they prolong or even amplify neurotransmitter signaling. Atypical inhibitors of DAT lack cocaine-like rewarding effects and offer a promising strategy for the treatment of drug use disorders. Here, we present the 3.2 Å resolution cryo-electron microscopy structure of the Drosophila melanogaster dopamine transporter (dDAT) in complex with the atypical non-competitive inhibitor AC-4-248. The inhibitor partially binds at the central binding site, extending into the extracellular vestibule, and locks the transporter in an outward open conformation. Our findings propose mechanisms for the non-competitive inhibition of DAT and attenuation of cocaine potency by AC-4-248 and provide a basis for the rational design of more efficacious atypical inhibitors.
RESUMO
The Na+,K+-ATPase generates electrochemical gradients of Na+ and K+ across the plasma membrane via a functional cycle that includes various phosphoenzyme intermediates. However, the structure and function of these intermediates and how metal fluorides mimick them require further investigation. Here, we describe a 4.0 Å resolution crystal structure and functional properties of the pig kidney Na+,K+-ATPase stabilized by the inhibitor beryllium fluoride (denoted E2-BeFx). E2-BeFx is expected to mimic properties of the E2P phosphoenzyme, yet with unknown characteristics of ion and ligand binding. The structure resembles the E2P form obtained by phosphorylation from inorganic phosphate (Pi) and stabilized by cardiotonic steroids, including a low-affinity Mg2+ site near ion binding site II. Our anomalous Fourier analysis of the crystals soaked in Rb+ (a K+ congener) followed by a low-resolution rigid-body refinement (6.9-7.5 Å) revealed preocclusion transitions leading to activation of the dephosphorylation reaction. We show that the Mg2+ location indicates a site of initial K+ recognition and acceptance upon binding to the outward-open E2P state after Na+ release. Furthermore, using binding and activity studies, we find that the BeFx-inhibited enzyme is also able to bind ADP/ATP and Na+. These results relate the E2-BeFx complex to a transient K+- and ADP-sensitive E∗P intermediate of the functional cycle of the Na+,K+-ATPase, prior to E2P.
Assuntos
Berílio , Glicosídeos Cardíacos , Fluoretos , Rim , ATPase Trocadora de Sódio-Potássio , Difosfato de Adenosina/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Berílio/química , Glicosídeos Cardíacos/química , Fluoretos/química , Rim/enzimologia , Cinética , Fosfatos/metabolismo , Fosforilação , Domínios Proteicos , ATPase Trocadora de Sódio-Potássio/antagonistas & inibidores , ATPase Trocadora de Sódio-Potássio/química , SuínosRESUMO
The sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 2a (SERCA2a) performs active reuptake of cytoplasmic Ca2+ and is a major regulator of cardiac muscle contractility. Dysfunction or dysregulation of SERCA2a is associated with heart failure, while restoring its function is considered as a therapeutic strategy to restore cardiac performance. However, its structure has not yet been determined. Based on native, active protein purified from pig ventricular muscle, we present the first crystal structures of SERCA2a, determined in the CPA-stabilized E2-AlF4- form (3.3 Å) and the Ca2+-occluded [Ca2]E1-AMPPCP form (4.0 Å). The structures are similar to the skeletal muscle isoform SERCA1a pointing to a conserved mechanism. We seek to explain the kinetic differences between SERCA1a and SERCA2a. We find that several isoform-specific residues are acceptor sites for post-translational modifications. In addition, molecular dynamics simulations predict that isoform-specific residues support distinct intramolecular interactions in SERCA2a and SERCA1a. Our experimental observations further indicate that isoform-specific intramolecular interactions are functionally relevant, and may explain the kinetic differences between SERCA2a and SERCA1a.
Assuntos
Coração/fisiologia , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/química , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/metabolismo , Sequência de Aminoácidos , Animais , Modelos Moleculares , Simulação de Dinâmica Molecular , Conformação Proteica , Processamento de Proteína Pós-Traducional , Homologia de Sequência , SuínosRESUMO
P-type ATPase are present in nearly all organisms. They maintain electrochemical gradients for many solutes, in particular ions, they control membrane lipid asymmetry, and are crucial components of intricate signaling networks. All P-type ATPases share a common topology with a transmembrane and three cytoplasmic domains and their transport cycle follows a general scheme - the Post-Albers-cycle. Recently, P-type ATPase research has been advanced most significantly by the technological advancements in cryo-EM analysis, which has elucidated many new P-type ATPase structures and mechanisms and revealed several new ways of regulation. In this review, we highlight the progress of the field and focus on special features that are present in the five subfamilies. Hence, we outline the new intersubunit transport model of KdpFABC, the ways in which heavy metal pumps have evolved to accommodate various substrates, the strategies Ca2+ pumps utilize to adapt to different environmental needs, the intricate molecular builds of the ion binding sites in Na,K- and H,K-ATPases, the remarkable hexameric assembly of fungal proton pumps, the many ways in which P4-ATPase lipid flippases are regulated, and finally the deorphanization of P5 pumps. Interestingly many of the described features are found in more than one of the five subfamilies, and mixed and matched together to provide optimal function and precise regulation.
Assuntos
ATPases do Tipo-P , ATPases do Tipo-P/metabolismo , Adenosina Trifosfatases/metabolismo , Lipídeos de Membrana/metabolismo , Transporte Biológico , Sítios de LigaçãoRESUMO
Plasma membrane ATPases are primary active transporters of cations that maintain steep concentration gradients. The ion gradients and membrane potentials derived from them form the basis for a range of essential cellular processes, in particular Na(+)-dependent and proton-dependent secondary transport systems that are responsible for uptake and extrusion of metabolites and other ions. The ion gradients are also both directly and indirectly used to control pH homeostasis and to regulate cell volume. The plasma membrane H(+)-ATPase maintains a proton gradient in plants and fungi and the Na(+),K(+)-ATPase maintains a Na(+) and K(+) gradient in animal cells. Structural information provides insight into the function of these two distinct but related P-type pumps.
Assuntos
Membrana Celular/metabolismo , ATPases Translocadoras de Prótons/química , ATPases Translocadoras de Prótons/metabolismo , ATPase Trocadora de Sódio-Potássio/química , ATPase Trocadora de Sódio-Potássio/metabolismo , Animais , Membrana Celular/química , HumanosRESUMO
Phosphorylation-type (P-type) ATPases are ubiquitous primary transporters that pump cations across cell membranes through the formation and breakdown of a phosphoenzyme intermediate. Structural investigations suggest that the transport mechanism is defined by conformational changes in the cytoplasmic domains of the protein that are allosterically coupled to transmembrane helices so as to expose ion binding sites to alternate sides of the membrane. Here, we have used single-molecule fluorescence resonance energy transfer to directly observe conformational changes associated with the functional transitions in the Listeria monocytogenes Ca2+-ATPase (LMCA1), an orthologue of eukaryotic Ca2+-ATPases. We identify key intermediates with no known crystal structures and show that Ca2+ efflux by LMCA1 is rate-limited by phosphoenzyme formation. The transport process involves reversible steps and an irreversible step that follows release of ADP and extracellular release of Ca2+.
Assuntos
Trifosfato de Adenosina/metabolismo , ATPases Transportadoras de Cálcio/química , ATPases Transportadoras de Cálcio/metabolismo , Transferência Ressonante de Energia de Fluorescência , Listeria monocytogenes/enzimologia , Imagem Individual de Molécula , Difosfato de Adenosina/metabolismo , Sítios de Ligação , Cálcio/metabolismo , Cinética , Modelos Moleculares , Fosforilação , Conformação ProteicaRESUMO
The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a P-type ATPase that transports Ca2+ from the cytosol into the sarco(endo)plasmic reticulum (SR/ER) lumen, driven by ATP. This primary transport activity depends on tight coupling between movements of the transmembrane helices forming the two Ca2+-binding sites and the cytosolic headpiece mediating ATP hydrolysis. We have addressed the molecular basis for this intramolecular communication by analyzing the structure and functional properties of the SERCA mutant E340A. The mutated Glu340 residue is strictly conserved among the P-type ATPase family of membrane transporters and is located at a seemingly strategic position at the interface between the phosphorylation domain and the cytosolic ends of 5 of SERCA's 10 transmembrane helices. The mutant displays a marked slowing of the Ca2+-binding kinetics, and its crystal structure in the presence of Ca2+ and ATP analog reveals a rotated headpiece, altered connectivity between the cytosolic domains, and an altered hydrogen bonding pattern around residue 340. Supported by molecular dynamics simulations, we conclude that the E340A mutation causes a stabilization of the Ca2+ sites in a more occluded state, hence displaying slowed dynamics. This finding underpins a crucial role of Glu340 in interdomain communication between the headpiece and the Ca2+-binding transmembrane region.
Assuntos
Proteínas de Ligação ao Cálcio/ultraestrutura , Cálcio/metabolismo , Conformação Proteica em alfa-Hélice , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/ultraestrutura , Trifosfato de Adenosina/química , Sequência de Aminoácidos/genética , Asparagina/química , Sítios de Ligação/genética , Cálcio/química , Sinalização do Cálcio/genética , Proteínas de Ligação ao Cálcio/química , Proteínas de Ligação ao Cálcio/genética , Cristalografia por Raios X , Citosol/metabolismo , Escherichia coli/enzimologia , Humanos , Ligação de Hidrogênio , Cinética , Simulação de Dinâmica Molecular , Mutação/genética , Fosforilação/genética , Domínios Proteicos/genética , Estrutura Secundária de Proteína , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/química , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/genética , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/metabolismo , Triptofano/químicaRESUMO
Heterozygous mutations in the ATP1A3 gene, coding for an alpha subunit isoform (α3) of Na+/K+-ATPase, are the primary genetic cause for rapid-onset dystonia-parkinsonism (RDP) and alternating hemiplegia of childhood (AHC). Recently, cerebellar ataxia, areflexia, pes cavus, optic atrophy and sensorineural hearing loss (CAPOS), early infantile epileptic encephalopathy (EIEE), childhood rapid onset ataxia (CROA) and relapsing encephalopathy with rapid onset ataxia (RECA) extend the clinical spectrum of ATP1A3 related disorders. AHC and RDP demonstrate distinct clinical features, with AHC symptoms being generally more severe compared to RDP. Currently, it is largely unknown what determines the disease severity, and whether severity is linked to the degree of functional impairment of the α3 subunit. Here we compared the effect of twelve different RDP and AHC specific mutations on the expression and function of the α3 Na+/K+-ATPase in transfected HEK cells and oocytes. All studied mutations led to functional impairment of the pump, as reflected by lower survival rate and reduced pump current. No difference in the extent of impairment, nor in the expression level, was found between the two phenotypes, suggesting that these measures of pump dysfunction do not exclusively determine the disease severity.
Assuntos
Distúrbios Distônicos/genética , Hemiplegia/genética , ATPase Trocadora de Sódio-Potássio/genética , ATPase Trocadora de Sódio-Potássio/metabolismo , Animais , Distúrbios Distônicos/metabolismo , Células HEK293 , Hemiplegia/metabolismo , Humanos , Mutação , XenopusRESUMO
BACKGROUND: Cell death triggered by unmitigated endoplasmic reticulum (ER) stress plays an important role in physiology and disease, but the death-inducing signaling mechanisms are incompletely understood. To gain more insight into these mechanisms, the ER stressor thapsigargin (Tg) is an instrumental experimental tool. Additionally, Tg forms the basis for analog prodrugs designed for cell killing in targeted cancer therapy. Tg induces apoptosis via the unfolded protein response (UPR), but how apoptosis is initiated, and how individual effects of the various UPR components are integrated, is unclear. Furthermore, the role of autophagy and autophagy-related (ATG) proteins remains elusive. METHODS: To systematically address these key questions, we analyzed the effects of Tg and therapeutically relevant Tg analogs in two human cancer cell lines of different origin (LNCaP prostate- and HCT116 colon cancer cells), using RNAi and inhibitory drugs to target death receptors, UPR components and ATG proteins, in combination with measurements of cell death by fluorescence imaging and propidium iodide staining, as well as real-time RT-PCR and western blotting to monitor caspase activity, expression of ATG proteins, UPR components, and downstream ER stress signaling. RESULTS: In both cell lines, Tg-induced cell death depended on death receptor 5 and caspase-8. Optimal cytotoxicity involved a non-autophagic function of MAP1LC3B upstream of procaspase-8 cleavage. PERK, ATF4 and CHOP were required for Tg-induced cell death, but surprisingly acted in parallel rather than as a linear pathway; ATF4 and CHOP were independently required for Tg-mediated upregulation of death receptor 5 and MAP1LC3B proteins, whereas PERK acted via other pathways. Interestingly, IRE1 contributed to Tg-induced cell death in a cell type-specific manner. This was linked to an XBP1-dependent activation of c-Jun N-terminal kinase, which was pro-apoptotic in LNCaP but not HCT116 cells. Molecular requirements for cell death induction by therapy-relevant Tg analogs were identical to those observed with Tg. CONCLUSIONS: Together, our results provide a new, integrated understanding of UPR signaling mechanisms and downstream mediators that induce cell death upon Tg-triggered, unmitigated ER stress. Video Abstract.
Assuntos
Estresse do Retículo Endoplasmático , Retículo Endoplasmático/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Tapsigargina/metabolismo , Resposta a Proteínas não Dobradas , Fator 4 Ativador da Transcrição/genética , Fator 4 Ativador da Transcrição/metabolismo , Autofagia , Caspase 8/genética , Caspase 8/metabolismo , Linhagem Celular Tumoral , Retículo Endoplasmático/genética , Humanos , Proteínas Quinases JNK Ativadas por Mitógeno/genética , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Proteínas Associadas aos Microtúbulos/genética , Receptores do Ligante Indutor de Apoptose Relacionado a TNF/genética , Receptores do Ligante Indutor de Apoptose Relacionado a TNF/metabolismo , Proteína 1 de Ligação a X-Box/genética , Proteína 1 de Ligação a X-Box/metabolismoRESUMO
Zinc is an essential micronutrient for all living organisms. It is required for signalling and proper functioning of a range of proteins involved in, for example, DNA binding and enzymatic catalysis. In prokaryotes and photosynthetic eukaryotes, Zn(2+)-transporting P-type ATPases of class IB (ZntA) are crucial for cellular redistribution and detoxification of Zn(2+) and related elements. Here we present crystal structures representing the phosphoenzyme ground state (E2P) and a dephosphorylation intermediate (E2·Pi) of ZntA from Shigella sonnei, determined at 3.2 Å and 2.7 Å resolution, respectively. The structures reveal a similar fold to Cu(+)-ATPases, with an amphipathic helix at the membrane interface. A conserved electronegative funnel connects this region to the intramembranous high-affinity ion-binding site and may promote specific uptake of cellular Zn(2+) ions by the transporter. The E2P structure displays a wide extracellular release pathway reaching the invariant residues at the high-affinity site, including C392, C394 and D714. The pathway closes in the E2·Pi state, in which D714 interacts with the conserved residue K693, which possibly stimulates Zn(2+) release as a built-in counter ion, as has been proposed for H(+)-ATPases. Indeed, transport studies in liposomes provide experimental support for ZntA activity without counter transport. These findings suggest a mechanistic link between PIB-type Zn(2+)-ATPases and PIII-type H(+)-ATPases and at the same time show structural features of the extracellular release pathway that resemble PII-type ATPases such as the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA) and Na(+), K(+)-ATPase. These findings considerably increase our understanding of zinc transport in cells and represent new possibilities for biotechnology and biomedicine.
Assuntos
Adenosina Trifosfatases/química , Adenosina Trifosfatases/metabolismo , Shigella/enzimologia , Trifosfato de Adenosina/metabolismo , Sítios de Ligação , Cádmio/metabolismo , ATPases Transportadoras de Cálcio/química , Sequência Conservada , Cristalografia por Raios X , Chumbo/metabolismo , Modelos Moleculares , Fosforilação , Proteolipídeos/química , Proteolipídeos/metabolismo , ATPases Translocadoras de Prótons/química , ATPases Translocadoras de Prótons/metabolismo , ATPase Trocadora de Sódio-Potássio/química , Zinco/metabolismoRESUMO
P-type ATPases transport ions across biological membranes against concentration gradients and are essential for all cells. They use the energy from ATP hydrolysis to propel large intramolecular movements, which drive vectorial transport of ions. Tight coordination of the motions of the pump is required to couple the two spatially distant processes of ion binding and ATP hydrolysis. Here, we review our current understanding of the structural dynamics of P-type ATPases, focusing primarily on Ca2+ pumps. We integrate different types of information that report on structural dynamics, primarily time-resolved fluorescence experiments including single-molecule Förster resonance energy transfer and molecular dynamics simulations, and interpret them in the framework provided by the numerous crystal structures of sarco/endoplasmic reticulum Ca2+-ATPase. We discuss the challenges in characterizing the dynamics of membrane pumps, and the likely impact of new technologies on the field.
Assuntos
Bombas de Íon/química , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/química , Trifosfato de Adenosina/metabolismo , Animais , Cálcio/metabolismo , Catálise , Humanos , Hidrólise , Bombas de Íon/metabolismo , Isoenzimas/química , Isoenzimas/metabolismo , Fosforilação , Ligação Proteica , Conformação Proteica , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/metabolismoRESUMO
Aquaporins of the TIP subfamily (Tonoplast Intrinsic Proteins) have been suggested to facilitate permeation of water and ammonia across the vacuolar membrane of plants, allowing the vacuole to efficiently sequester ammonium ions and counteract cytosolic fluctuations of ammonia. Here, we report the structure determined at 1.18 Å resolution from twinned crystals of Arabidopsis thaliana aquaporin AtTIP2;1 and confirm water and ammonia permeability of the purified protein reconstituted in proteoliposomes as further substantiated by molecular dynamics simulations. The structure of AtTIP2;1 reveals an extended selectivity filter with the conserved arginine of the filter adopting a unique unpredicted position. The relatively wide pore and the polar nature of the selectivity filter clarify the ammonia permeability. By mutational studies, we show that the identified determinants in the extended selectivity filter region are sufficient to convert a strictly water-specific human aquaporin into an AtTIP2;1-like ammonia channel. A flexible histidine and a novel water-filled side pore are speculated to deprotonate ammonium ions, thereby possibly increasing permeation of ammonia. The molecular understanding of how aquaporins facilitate ammonia flux across membranes could potentially be used to modulate ammonia losses over the plasma membrane to the atmosphere, e.g., during photorespiration, and thereby to modify the nitrogen use efficiency of plants.