RESUMEN
It has been proposed that the local segregation of kinases and the tyrosine phosphatase CD45 underpins T cell antigen receptor (TCR) triggering, but how such segregation occurs and whether it can initiate signaling is unclear. Using structural and biophysical analysis, we show that the extracellular region of CD45 is rigid and extends beyond the distance spanned by TCR-ligand complexes, implying that sites of TCR-ligand engagement would sterically exclude CD45. We also show that the formation of 'close contacts', new structures characterized by spontaneous CD45 and kinase segregation at the submicron-scale, initiates signaling even when TCR ligands are absent. Our work reveals the structural basis for, and the potent signaling effects of, local CD45 and kinase segregation. TCR ligands have the potential to heighten signaling simply by holding receptors in close contacts.
Asunto(s)
Antígenos Comunes de Leucocito/inmunología , Receptores de Antígenos de Linfocitos T/inmunología , Transducción de Señal/inmunología , Linfocitos T/inmunología , Cristalografía por Rayos X , Células HEK293 , Humanos , Células Jurkat , Antígenos Comunes de Leucocito/química , Antígenos Comunes de Leucocito/metabolismo , Proteína Tirosina Quinasa p56(lck) Específica de Linfocito/inmunología , Proteína Tirosina Quinasa p56(lck) Específica de Linfocito/metabolismo , Microscopía Electrónica , Microscopía Fluorescente/métodos , Modelos Moleculares , Estructura Terciaria de Proteína , Receptores de Antígenos de Linfocitos T/metabolismo , Linfocitos T/metabolismo , Factores de Tiempo , Proteína Tirosina Quinasa ZAP-70/inmunología , Proteína Tirosina Quinasa ZAP-70/metabolismoRESUMEN
MicroRNAs (miRNAs) are versatile regulators of gene expression in higher eukaryotes. In order to silence many different mRNAs in a precise manner, miRNA stability and efficacy is controlled by highly developed regulatory pathways and fine-tuning mechanisms both affecting miRNA processing and altering mature miRNA target specificity.
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Regulación de la Expresión Génica , MicroARNs/genética , Animales , Humanos , MicroARNs/química , MicroARNs/metabolismo , Procesamiento Postranscripcional del ARN , Ribonucleasa III/metabolismoRESUMEN
Perforin-2 (PFN2, MPEG1) is a key pore-forming protein in mammalian innate immunity restricting intracellular bacteria proliferation. It forms a membrane-bound pre-pore complex that converts to a pore-forming structure upon acidification; but its mechanism of conformational transition has been debated. Here we used cryo-electron microscopy, tomography and subtomogram averaging to determine structures of PFN2 in pre-pore and pore conformations in isolation and bound to liposomes. In isolation and upon acidification, the pre-assembled complete pre-pore rings convert to pores in both flat ring and twisted conformations. On membranes, in situ assembled PFN2 pre-pores display various degrees of completeness; whereas PFN2 pores are mainly incomplete arc structures that follow the same subunit packing arrangements as found in isolation. Both assemblies on membranes use their P2 ß-hairpin for binding to the lipid membrane surface. Overall, these structural snapshots suggest a molecular mechanism for PFN2 pre-pore to pore transition on a targeted membrane, potentially using the twisted pore as an intermediate or alternative state to the flat conformation, with the capacity to cause bilayer distortion during membrane insertion.
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Liposomas , Mamíferos , Animales , Microscopía por Crioelectrón , Perforina/análisis , Perforina/química , Perforina/metabolismo , Membrana Celular/metabolismo , Liposomas/metabolismo , MembranasRESUMEN
The European Biophysics Journal Prizes awarded at the European Biophysical Societies Association (EBSA) Congress in Stockholm in the Summer of 2023 recognised papers published in 2020 and 2021 which made use of multiple complementing experimental, theoretical and computational approaches. One of the winning papers addressed the specific role of arginine residues within antimicrobial and cell-penetrating peptides, in promoting membrane defect stabilisation and pore formation. The other winning paper described the influence of atomic force microscopy probe geometry on the measurement of surface deformability, assessed for investigation of the differing viscoelastic properties of non-malignant and cancerous cells. These papers showcase biophysical science; the importance of combining different experimental, modelling and molecular dynamics methods; and how researchers need to understand the theoretical basis and the limitations of the techniques they use. EBSA warmly congratulates the authors on their work and its subsequent recognition. Publication of these papers also demonstrates the ongoing commitment of the European Biophysics Journal to molecular scale and to systems biophysics, and to support of the international biophysical community.
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Distinciones y Premios , Membrana Celular , Biofisica , Microscopía de Fuerza Atómica , PéptidosRESUMEN
Pore-forming proteins (PFPs) interact with lipid bilayers to compromise membrane integrity. Many PFPs function by inserting a ring of oligomerized subunits into the bilayer to form a protein-lined hydrophilic channel. However, mounting evidence suggests that PFPs can also generate 'proteolipidic' pores by contributing to the fusion of inner and outer bilayer leaflets to form a toroidal structure. We discuss here toroidal pore formation by peptides including melittin, protegrin, and Alzheimer's Aß1-41, as well as by PFPs from several evolutionarily unrelated families: the colicin/Bcl-2 grouping including the pro-apoptotic protein Bax, actinoporins derived from sea anemones, and the membrane attack complex-perforin/cholesterol dependent cytolysin (MACPF/CDC) set of proteins. We also explore how the structure and biological role of toroidal pores might be investigated further.
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Membrana Celular/química , Membrana Dobles de Lípidos/química , Lípidos de la Membrana/química , Proteínas Citotóxicas Formadoras de Poros/química , Membrana Celular/metabolismo , Colicinas/química , Colicinas/metabolismo , Membrana Dobles de Lípidos/metabolismo , Meliteno/química , Meliteno/metabolismo , Lípidos de la Membrana/metabolismo , Modelos Moleculares , Proteínas Citotóxicas Formadoras de Poros/metabolismo , Unión Proteica , Estructura Secundaria de Proteína , Estructura Terciaria de ProteínaRESUMEN
Hantaviruses are zoonotic pathogens that cause severe hemorrhagic fever and pulmonary syndrome. The outer membrane of the hantavirus envelope displays a lattice of two glycoproteins, Gn and Gc, which orchestrate host cell recognition and entry. Here, we describe the crystal structure of the Gn glycoprotein ectodomain from the Asiatic Hantaan virus (HTNV), the most prevalent pathogenic hantavirus. Structural overlay analysis reveals that the HTNV Gn fold is highly similar to the Gn of Puumala virus (PUUV), a genetically and geographically distinct and less pathogenic hantavirus found predominantly in northeastern Europe, confirming that the hantaviral Gn fold is architecturally conserved across hantavirus clades. Interestingly, HTNV Gn crystallized at acidic pH, in a compact tetrameric configuration distinct from the organization at neutral pH. Analysis of the Gn, both in solution and in the context of the virion, confirms the pH-sensitive oligomeric nature of the glycoprotein, indicating that the hantaviral Gn undergoes structural transitions during host cell entry. These data allow us to present a structural model for how acidification during endocytic uptake of the virus triggers the dissociation of the metastable Gn-Gc lattice to enable insertion of the Gc-resident hydrophobic fusion loops into the host cell membrane. Together, these data reveal the dynamic plasticity of the structurally conserved hantaviral surface.IMPORTANCE Although outbreaks of Korean hemorrhagic fever were first recognized during the Korean War (1950 to 1953), it was not until 1978 that they were found to be caused by Hantaan virus (HTNV), the most prevalent pathogenic hantavirus. Here, we describe the crystal structure of HTNV envelope glycoprotein Gn, an integral component of the Gn-Gc glycoprotein spike complex responsible for host cell entry. HTNV Gn is structurally conserved with the Gn of a genetically and geographically distal hantavirus, Puumala virus, indicating that the observed α/ß fold is well preserved across the Hantaviridae family. The combination of our crystal structure with solution state analysis of recombinant protein and electron cryo-microscopy of acidified hantavirus allows us to propose a model for endosome-induced reorganization of the hantaviral glycoprotein lattice. This provides a molecular-level rationale for the exposure of the hydrophobic fusion loops on the Gc, a process required for fusion of viral and cellular membranes.
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Glicoproteínas/química , Infecciones por Hantavirus/metabolismo , Orthohantavirus/fisiología , Proteínas del Envoltorio Viral/química , Virión/fisiología , Animales , Chlorocebus aethiops , Microscopía por Crioelectrón , Orthohantavirus/ultraestructura , Infecciones por Hantavirus/virología , Humanos , Modelos Moleculares , Filogenia , Estructura Terciaria de Proteína , Virus Puumala/química , Células Vero , Virión/ultraestructuraRESUMEN
Kindlins co-activate integrins alongside talin. They possess, like talin, a FERM domain (4.1-erythrin-radixin-moiesin domain) comprising F0-F3 subdomains, but with a pleckstrin homology (PH) domain inserted in the F2 subdomain that enables membrane association. We present the crystal structure of murine kindlin-3 PH domain determined at a resolution of 2.23â Å and characterise its lipid binding using biophysical and computational approaches. Molecular dynamics simulations suggest flexibility in the PH domain loops connecting ß-strands forming the putative phosphatidylinositol phosphate (PtdInsP)-binding site. Simulations with PtdInsP-containing bilayers reveal that the PH domain associates with PtdInsP molecules mainly via the positively charged surface presented by the ß1-ß2 loop and that it binds with somewhat higher affinity to PtdIns(3,4,5)P3 compared with PtdIns(4,5)P2 Surface plasmon resonance (SPR) with lipid headgroups immobilised and the PH domain as an analyte indicate affinities of 300â µM for PtdIns(3,4,5)P3 and 1â mM for PtdIns(4,5)P2 In contrast, SPR studies with an immobilised PH domain and lipid nanodiscs as the analyte show affinities of 0.40â µM for PtdIns(3,4,5)P3 and no affinity for PtdIns(4,5)P2 when the inositol phosphate constitutes 5% of the total lipids (â¼5 molecules per nanodisc). Reducing the PtdIns(3,4,5)P3 composition to 1% abolishes nanodisc binding to the PH domain, as does site-directed mutagenesis of two lysines within the ß1-ß2 loop. Binding of PtdIns(3,4,5)P3 by a canonical PH domain, Grp1, is not similarly influenced by SPR experimental design. These data suggest a role for PtdIns(3,4,5)P3 clustering in the binding of some PH domains and not others, highlighting the importance of lipid mobility and clustering for the biophysical assessment of protein-membrane interactions.
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Proteínas del Citoesqueleto/química , Fosfatidilcolinas/química , Fosfatidilinositoles/química , Fosfatidilserinas/química , Dominios Homólogos a Pleckstrina , Receptores Citoplasmáticos y Nucleares/química , Secuencia de Aminoácidos , Animales , Sitios de Unión , Clonación Molecular , Cristalografía por Rayos X , Proteínas del Citoesqueleto/genética , Proteínas del Citoesqueleto/metabolismo , Escherichia coli/genética , Escherichia coli/metabolismo , Expresión Génica , Cinética , Ratones , Simulación de Dinámica Molecular , Fosfatidilcolinas/metabolismo , Fosfatidilinositoles/metabolismo , Fosfatidilserinas/metabolismo , Unión Proteica , Conformación Proteica en Hélice alfa , Conformación Proteica en Lámina beta , Dominios y Motivos de Interacción de Proteínas , Receptores Citoplasmáticos y Nucleares/genética , Receptores Citoplasmáticos y Nucleares/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Alineación de Secuencia , Homología de Secuencia de AminoácidoRESUMEN
Pore-forming proteins and peptides act on their targeted lipid bilayer membranes to increase permeability. This approach to the modulation of biological function is relevant to a great number of living processes, including; infection, parasitism, immunity, apoptosis, development and neurodegeneration. While some pore-forming proteins/peptides assemble into rings of subunits to generate discrete, well-defined pore-forming structures, an increasing number is recognised to form pores via mechanisms which co-opt membrane lipids themselves. Among these, membrane attack complex-perforin/cholesterol-dependent cytolysin (MACPF/CDC) family proteins, Bax/colicin family proteins and actinoporins are especially prominent and among the mechanisms believed to apply are the formation of non-lamellar (semi-toroidal or toroidal) lipidic structures. In this review I focus on the ways in which lipids contribute to pore formation and contrast this with the ways in which lipids are co-opted also in membrane fusion and fission events. A variety of mechanisms for pore formation that involve lipids exists, but they consistently result in stable hybrid proteolipidic structures. These structures are stabilised by mechanisms in which pore-forming proteins modify the innate capacity of lipid membranes to respond to their environment, changing shape and/or phase and binding individual lipid molecules directly. In contrast, and despite the diversity in fusion protein types, mechanisms for membrane fusion are rather similar to each other, mapping out a pathway from pairs of separated compartments to fully confluent fused membranes. Fusion proteins generate metastable structures along the way which, like long-lived proteolipidic pore-forming complexes, rely on the basic physical properties of lipid bilayers. Membrane fission involves similar intermediates, in the reverse order. I conclude by considering the possibility that at least some pore-forming and fusion proteins are evolutionarily related homologues. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale.
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Membrana Celular , Colicinas , Fusión de Membrana , Lípidos de la Membrana , Perforina , Proteína X Asociada a bcl-2 , Animales , Membrana Celular/química , Membrana Celular/metabolismo , Colicinas/química , Colicinas/metabolismo , Humanos , Lípidos de la Membrana/química , Lípidos de la Membrana/metabolismo , Perforina/química , Perforina/metabolismo , Proteína X Asociada a bcl-2/química , Proteína X Asociada a bcl-2/metabolismoRESUMEN
Terminal uridylyl transferases (TUTs) are responsible for the post-transcriptional addition of uridyl residues to RNA 3' ends, leading in some cases to altered stability. The Schizosaccharomyces pombe TUT Cid1 is a model enzyme that has been characterized structurally at moderate resolution and provides insights into the larger and more complex mammalian TUTs, ZCCHC6 and ZCCHC11. Here, we report a higher resolution (1.74 Å) crystal structure of Cid1 that provides detailed evidence for uracil selection via the dynamic flipping of a single histidine residue. We also describe a novel closed conformation of the enzyme that may represent an intermediate stage in a proposed product ejection mechanism. The structural insights gained, combined with normal mode analysis and biochemical studies, demonstrate that the plasticity of Cid1, particularly about a hinge region (N164-N165), is essential for catalytic activity, and provide an explanation for its distributive uridylyl transferase activity. We propose a model clarifying observed differences between the in vitro apparently processive activity and in vivo distributive monouridylylation activity of Cid1. We suggest that modulating the flexibility of such enzymes-for example by the binding of protein co-factors-may allow them alternatively to add single or multiple uridyl residues to the 3' termini of RNA molecules.
Asunto(s)
Nucleotidiltransferasas/metabolismo , ARN Nucleotidiltransferasas/metabolismo , ARN de Hongos/metabolismo , Proteínas de Schizosaccharomyces pombe/metabolismo , Biocatálisis , Dominio Catalítico , Cristalografía por Rayos X , Modelos Moleculares , Mutación , Nucleotidiltransferasas/química , Nucleotidiltransferasas/genética , Estructura Terciaria de Proteína , ARN Nucleotidiltransferasas/química , ARN Nucleotidiltransferasas/genética , ARN de Hongos/genética , Rotación , Schizosaccharomyces/enzimología , Schizosaccharomyces/genética , Proteínas de Schizosaccharomyces pombe/química , Proteínas de Schizosaccharomyces pombe/genética , Uridina Trifosfato/metabolismoRESUMEN
Most membrane attack complex-perforin/cholesterol-dependent cytolysin (MACPF/CDC) proteins are thought to form pores in target membranes by assembling into pre-pore oligomers before undergoing a pre-pore to pore transition. Assembly during pore formation is into both full rings of subunits and incomplete rings (arcs). The balance between arcs and full rings is determined by a mechanism dependent on protein concentration in which arc pores arise due to kinetic trapping of the pre-pore forms by the depletion of free protein subunits during oligomerization. Here we describe the use of a kinetic assay to study pore formation in red blood cells by the MACPF/CDC pneumolysin from Streptococcus pneumoniae. We show that cell lysis displays two kinds of dependence on protein concentration. At lower concentrations, it is dependent on the pre-pore to pore transition of arc oligomers, which we show to be a cooperative process. At higher concentrations, it is dependent on the amount of pneumolysin bound to the membrane and reflects the affinity of the protein for its receptor, cholesterol. A lag occurs before cell lysis begins; this is dependent on oligomerization of pneumolysin. Kinetic dissection of cell lysis by pneumolysin demonstrates the capacity of MACPF/CDCs to generate pore-forming oligomeric structures of variable size with, most likely, different functional roles in biology.
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Estreptolisinas/química , Estreptolisinas/metabolismo , Animales , Proteínas Bacterianas/química , Proteínas Bacterianas/metabolismo , Eritrocitos/metabolismo , Cinética , Porosidad , OvinosRESUMEN
Hedgehog (Hh) morphogens play fundamental roles during embryogenesis and adulthood, in health and disease. Multiple cell surface receptors regulate the Hh signaling pathway. Among these, the glycosaminoglycan (GAG) chains of proteoglycans shape Hh gradients and signal transduction. We have determined crystal structures of Sonic Hh complexes with two GAGs, heparin and chondroitin sulfate. The interaction determinants, confirmed by site-directed mutagenesis and binding studies, reveal a previously not identified Hh site for GAG binding, common to all Hh proteins. The majority of Hh residues forming this GAG-binding site have been previously implicated in developmental diseases. Crystal packing analysis, combined with analytical ultracentrifugation of Sonic Hh-GAG complexes, suggests a potential mechanism for GAG-dependent Hh multimerization. Taken together, these results provide a direct mechanistic explanation of the observed correlation between disease and impaired Hh gradient formation. Moreover, GAG binding partially overlaps with the site of Hh interactions with an array of protein partners including Patched, hedgehog interacting protein, and the interference hedgehog protein family, suggesting a unique mechanism of Hh signaling modulation.
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Glicosaminoglicanos/metabolismo , Proteínas Hedgehog/química , Proteínas Hedgehog/metabolismo , Modelos Moleculares , Conformación Proteica , Proteoglicanos/metabolismo , Transducción de Señal/fisiología , Cromatografía de Afinidad , Escherichia coli , Glicosaminoglicanos/química , Humanos , Mutagénesis Sitio-Dirigida , Polimerizacion , UltracentrifugaciónRESUMEN
Membrane Attack Complex/Perforin (MACPF) and Cholesterol-Dependent Cytolysins (CDC) form the MACPF/CDC superfamily of important effector proteins widespread in nature. MACPFs and CDCs were discovered separately with no sequence similarity at that stage being apparent between the two protein families such that they were not, until recently, considered evolutionary related. The breakthrough showing they are came with recent structural work that also shed light on the molecular mechanism of action of various MACPF proteins. Similarity in structural properties and conserved functional features indicate that both protein families have the same evolutionary origin. We will describe the distribution of MACPF/CDC proteins in nature and discuss briefly their similarity and functional role in different biological processes.
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Complejo de Ataque a Membrana del Sistema Complemento/clasificación , Citotoxinas/clasificación , Perforina/genética , Secuencia de Aminoácidos , Animales , Colesterol/química , Colesterol/fisiología , Complejo de Ataque a Membrana del Sistema Complemento/química , Complejo de Ataque a Membrana del Sistema Complemento/genética , Citotoxinas/química , Citotoxinas/genética , Evolución Molecular , Humanos , Modelos Moleculares , Datos de Secuencia Molecular , Perforina/química , Perforina/metabolismo , FilogeniaRESUMEN
Recent work on the MACPF/CDC superfamily of pore-forming proteins has focused on the structural analysis of monomers and pore-forming oligomeric complexes. We set the family of proteins in context and highlight aspects of their function which the direct and exclusive equation of oligomers with pores fails to explain. Starting with a description of the distribution of MACPF/CDC proteins across the domains of life, we proceed to show how their evolutionary relationships can be understood on the basis of their structural homology and re-evaluate models for pore formation by perforin, in particular. We furthermore highlight data showing the role of incomplete oligomeric rings (arcs) in pore formation and how this can explain small pores generated by oligomers of proteins belonging to the family. We set this in the context of cell biological and biophysical data on the proteins' function and discuss how this helps in the development of an understanding of how they act in processes such as apicomplexan parasites gliding through cells and exiting from cells.
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Membrana Celular/metabolismo , Complejo de Ataque a Membrana del Sistema Complemento/metabolismo , Citotoxinas/metabolismo , Modelos Moleculares , Perforina/metabolismo , Filogenia , Conformación Proteica , Secuencia de Aminoácidos , Apicomplexa , Bacterias , Complejo de Ataque a Membrana del Sistema Complemento/química , Complejo de Ataque a Membrana del Sistema Complemento/genética , Citotoxinas/química , Datos de Secuencia Molecular , Perforina/química , Polimerizacion , Alineación de SecuenciaRESUMEN
Programmed -1 ribosomal frameshifting is employed in the expression of a number of viral and cellular genes. In this process, the ribosome slips backwards by a single nucleotide and continues translation of an overlapping reading frame, generating a fusion protein. Frameshifting signals comprise a heptanucleotide slippery sequence, where the ribosome changes frame, and a stimulatory RNA structure, a stem-loop or RNA pseudoknot. Antisense oligonucleotides annealed appropriately 3' of a slippery sequence have also shown activity in frameshifting, at least in vitro. Here we examined frameshifting at the U6A slippery sequence of the HIV gag/pol signal and found high levels of both -1 and -2 frameshifting with stem-loop, pseudoknot or antisense oligonucleotide stimulators. By examining -1 and -2 frameshifting outcomes on mRNAs with varying slippery sequence-stimulatory RNA spacing distances, we found that -2 frameshifting was optimal at a spacer length 1-2 nucleotides shorter than that optimal for -1 frameshifting with all stimulatory RNAs tested. We propose that the shorter spacer increases the tension on the mRNA such that when the tRNA detaches, it more readily enters the -2 frame on the U6A heptamer. We propose that mRNA tension is central to frameshifting, whether promoted by stem-loop, pseudoknot or antisense oligonucleotide stimulator.
Asunto(s)
Sistema de Lectura Ribosómico , ARN Mensajero/química , Animales , Células COS , Chlorocebus aethiops , Espectrometría de Masas , Oligonucleótidos Antisentido/metabolismo , Biosíntesis de Proteínas , ARN Mensajero/metabolismo , TransfecciónRESUMEN
The cytotoxic cell granule secretory pathway is essential for immune defence. How the pore-forming protein perforin (PFN) facilitates the cytosolic delivery of granule-associated proteases (granzymes) remains enigmatic. Here we show that PFN is able to induce invaginations and formation of complete internal vesicles in giant unilamellar vesicles. Formation of internal vesicles depends on native PFN and calcium and antibody labeling shows the localization of PFN at the invaginations. This vesiculation is recapitulated in large unilamellar vesicles and in this case PFN oligomers can be seen associated with the necks of the invaginations. Capacitance measurements show PFN is able to increase a planar lipid membrane surface area in the absence of pore formation, in agreement with the ability to induce invaginations. Finally, addition of PFN to Jurkat cells causes the formation of internal vesicles prior to pore formation. PFN is capable of triggering an endocytosis-like event in addition to pore formation, suggesting a new paradigm for its role in delivering apoptosis-inducing granzymes into target cells.
Asunto(s)
Membrana Celular/metabolismo , Endocitosis/fisiología , Granzimas/metabolismo , Inmunidad Innata/fisiología , Perforina/metabolismo , Vesículas Secretoras/metabolismo , Microscopía por Crioelectrón , Humanos , Células Jurkat , Microscopía Fluorescente , Perforina/inmunología , Perforina/fisiologíaRESUMEN
Tumor-suppressor let-7 pre-microRNAs (miRNAs) are regulated by terminal uridylyltransferases TUT7 and TUT4 that either promote let-7 maturation by adding a single uridine nucleotide to the pre-miRNA 3' end or mark them for degradation by the addition of multiple uridines. Oligo-uridylation is increased in cells by enhanced TUT7/4 expression and especially by the RNA-binding pluripotency factor LIN28A. Using cryogenic electron microscopy, we captured high-resolution structures of active forms of TUT7 alone, of TUT7 plus pre-miRNA and of both TUT7 and TUT4 bound with pre-miRNA and LIN28A. Our structures reveal that pre-miRNAs engage the enzymes in fundamentally different ways depending on the presence of LIN28A, which clamps them onto the TUTs to enable processive 3' oligo-uridylation. This study reveals the molecular basis for mono- versus oligo-uridylation by TUT7/4, as determined by the presence of LIN28A, and thus their mechanism of action in the regulation of cell fate and in cancer.
RESUMEN
Kindlin-3, a 75-kDa protein, has been shown to be critical for hemostasis, immunity, and bone metabolism via its role in integrin activation. The Kindlin family is hallmarked by a FERM domain comprised of F1, F2, and F3 subdomains together with an N-terminal F0 domain and a pleckstrin homology domain inserted in the F2 domain. Recombinant Kindlin-3 was cloned, expressed, and purified, and its domain organization was studied by x-ray scattering and other techniques to reveal an extended conformation. This unusual elongated structure is similar to that found in the paralogue Talin head domain. Analytical ultracentrifugation experiments indicated that Kindlin-3 forms a ternary complex with the Talin and ß-integrin cytoplasmic tails. NMR showed that Kindlin-3 specifically recognizes the membrane-distal tail NPXY motif in both the ß(1A) and ß(1D) isoforms, although the interaction is stronger with ß(1A). An upstream Ser/Thr cluster in the tails also plays a critical role. Overall these data support current biological, clinical, and mutational data on Kindlin-3/ß-tail binding and provide novel insights into the overall conformation and interactions of Kindlin-3.
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Secuencias de Aminoácidos , Proteínas del Citoesqueleto/química , Integrina beta1/química , Conformación Proteica , Secuencia de Aminoácidos , Animales , Fenómenos Biofísicos , Proteínas del Citoesqueleto/genética , Proteínas del Citoesqueleto/metabolismo , Integrina beta1/metabolismo , Espectroscopía de Resonancia Magnética , Proteínas de la Membrana/química , Proteínas de la Membrana/metabolismo , Ratones , Mutación , Unión Proteica , Isoformas de Proteínas/química , Isoformas de Proteínas/metabolismo , Estructura Terciaria de Proteína , Subunidades de Proteína/química , Subunidades de Proteína/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Dispersión del Ángulo Pequeño , Células Sf9 , Talina/química , Talina/metabolismo , Difracción de Rayos XRESUMEN
Inside-out activation of integrins is mediated via the binding of talin and kindlin to integrin ß-subunit cytoplasmic tails. The kindlin FERM domain is interrupted by a pleckstrin homology (PH) domain within its F2 subdomain. Here, we present data confirming the importance of the kindlin-1 PH domain for integrin activation and its x-ray crystal structure at a resolution of 2.1 Å revealing a C-terminal second α-helix integral to the domain but found only in the kindlin protein family. An isoform-specific salt bridge occludes the canonical phosphoinositide binding site, but molecular dynamics simulations display transient switching to an alternative open conformer. Molecular docking reveals that the opening of the pocket would enable potential ligands to bind within it. Although lipid overlay assays suggested the PH domain binds inositol monophosphates, surface plasmon resonance demonstrated weak affinities for inositol 3,4,5-triphosphate (Ins(3,4,5)P(3); K(D) â¼100 µM) and no monophosphate binding. Removing the salt bridge by site-directed mutagenesis increases the PH domain affinity for Ins(3,4,5)P(3) as measured by surface plasmon resonance and enables it to bind PtdIns(3,5)P(2) on a dot-blot. Structural comparison with other PH domains suggests that the phosphate binding pocket in the kindlin-1 PH domain is more occluded than in kindlins-2 and -3 due to its salt bridge. In addition, the apparent affinity for Ins(3,4,5)P(3) is affected by the presence of PO(4) ions in the buffer. We suggest the physiological ligand of the kindlin-1 PH domain is most likely not an inositol phosphate but another phosphorylated species.
Asunto(s)
Proteínas Portadoras/química , Simulación de Dinámica Molecular , Animales , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Cristalografía por Rayos X , Ratones , Mutagénesis , Fosfatos/química , Fosfatos/metabolismo , Fosfatos de Fosfatidilinositol/química , Fosfatos de Fosfatidilinositol/genética , Fosfatos de Fosfatidilinositol/metabolismo , Unión Proteica , Estructura Secundaria de Proteína , Estructura Terciaria de Proteína , Relación Estructura-ActividadRESUMEN
Perforin (PFN) is a pore-forming protein produced by cytotoxic lymphocytes that aids in the clearance of tumor or virus-infected cells by a mechanism that involves the formation of transmembrane pores. The properties of PFN pores and the mechanism of their assembly remain unclear. Here, we studied pore characteristics by functional and structural methods to show that perforin forms pores more heterogeneous than anticipated. Planar lipid bilayer experiments indicate that perforin pores exhibit a broad range of conductances, from 0.15 to 21 nanosiemens. In comparison with large pores that possessed low noise and remained stably open, small pores exhibited high noise and were very unstable. Furthermore, the opening step and the pore size were dependent on the lipid composition of the membrane. The heterogeneity in pore sizes was confirmed with cryo-electron microscopy and showed a range of sizes matching that observed in the conductance measurements. Furthermore, two different membrane-bound PFN conformations were observed, interpreted as pre-pore and pore states of the protein. The results collectively indicate that PFN forms heterogeneous pores through a multistep mechanism and provide a new paradigm for understanding the range of different effects of PFN and related membrane attack complex/perforin domain proteins observed in vivo and in vitro.