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This paper provides an overview of the Curiosity rover's exploration at Vera Rubin ridge (VRR) and summarizes the science results. VRR is a distinct geomorphic feature on lower Aeolis Mons (informally known as Mount Sharp) that was identified in orbital data based on its distinct texture, topographic expression, and association with a hematite spectral signature. Curiosity conducted extensive remote sensing observations, acquired data on dozens of contact science targets, and drilled three outcrop samples from the ridge, as well as one outcrop sample immediately below the ridge. Our observations indicate that strata composing VRR were deposited in a predominantly lacustrine setting and are part of the Murray formation. The rocks within the ridge are chemically in family with underlying Murray formation strata. Red hematite is dispersed throughout much of the VRR bedrock, and this is the source of the orbital spectral detection. Gray hematite is also present in isolated, gray-colored patches concentrated toward the upper elevations of VRR, and these gray patches also contain small, dark Fe-rich nodules. We propose that VRR formed when diagenetic event(s) preferentially hardened rocks, which were subsequently eroded into a ridge by wind. Diagenesis also led to enhanced crystallization and/or cementation that deepened the ferric-related spectral absorptions on the ridge, which helped make them readily distinguishable from orbit. Results add to existing evidence of protracted aqueous environments at Gale crater and give new insight into how diagenesis shaped Mars' rock record.
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The article "A Mixed Methods Evaluation of Early Childhood Abuse Prevention Within Evidence-Based Home Visiting Programs", written by M. Matone, K. Kellom, H. Griffis, W. Quarshie, J. Faerber, P. Gierlach, J. Whittaker, D. M. Rubin and P. F. Cronholm, was originally published electronically on the publisher's internet portal (currently SpringerLink) on 31 May 2018 without open access. With the author(s)' decision to opt for Open Choice the copyright of the article changed on 27 July 2018 to
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Objectives In this large scale, mixed methods evaluation, we determined the impact and context of early childhood home visiting on rates of child abuse-related injury. Methods Entropy-balanced and propensity score matched retrospective cohort analysis comparing children of Pennsylvania Nurse-Family Partnership (NFP), Parents As Teachers (PAT), and Early Head Start (EHS) enrollees and children of Pennsylvania Medicaid eligible women from 2008 to 2014. Abuse-related injury episodes were identified in medical assistance claims with ICD-9 codes. Weighted frequencies and logistic regression odds of injury within 24 months are presented. In-depth interviews with staff and clients (n = 150) from 11 programs were analyzed using a modified grounded theory approach. Results The odds of a healthcare encounter for early childhood abuse among clients were significantly greater than comparison children (NFP: 1.32, 95% CI [1.08, 1.62]; PAT: 4.11, 95% CI [1.60, 10.55]; EHS: 3.15, 95% CI [1.41, 7.06]). Qualitative data illustrated the circumstances of and program response to client issues related to child maltreatment, highlighting the role of non-client caregivers. All stakeholders described curricular content aimed at prevention (e.g. positive parenting) with little time dedicated to addressing current or past abuse. Clients who reported a lack of abuse-related content supposed their home visitor's assumption of an absence of risk in their home, but were supportive of the introduction of abuse-related content. Approach, acceptance, and available resources were mediators of successfully addressing abuse. Conclusions for Practice Home visiting aims to prevent child abuse among high-risk families. Adequate home visitor capacity to proactively assess abuse risk, deliver effective preventive curriculum with fidelity to caregivers, and access appropriate resources is necessary.
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Técnicos Medios en Salud/psicología , Maltrato a los Niños/prevención & control , Familia/psicología , Servicios de Atención de Salud a Domicilio/organización & administración , Visita Domiciliaria/estadística & datos numéricos , Responsabilidad Parental/psicología , Padres/educación , Evaluación de Programas y Proyectos de Salud/métodos , Adulto , Niño , Preescolar , Femenino , Humanos , Masculino , Conducta Materna , Pennsylvania , Investigación Cualitativa , Estudios Retrospectivos , Adulto JovenRESUMEN
The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large-ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 µm and 350 µm with an intermediate axis mean size of 113 µm (median: 103 µm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.
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Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter- to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.
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The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).
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Lagos , Marte , Clima , Exhumación , PaleontologíaRESUMEN
During extracorporeal procedures like hemodialysis, heparin is administered to patients to prevent clotting. Unfractionated heparin has side effects such as excessive bleeding. It would be advantageous if the blood could be deheparinased before it returns to the patient. Previous work has indicated that poly-L-lysine/alginate beads can efficiently remove heparin from saline solutions 1. Heparin is irreversibly absorbed onto the beads. This article explores ways of optimizing the absorption process by performing in vitro rate experiments with varying physical parameters of the beads. Fetal calf serum and blood are also used in experiments to investigate the possibility of designing a safe and efficient reactor to absorb heparin. All the experiments were performed to obtain the required parameters for optimal reactor design. The results indicate that the absorption could be optimized by controlling the membrane thickness of the beads. The beads also showed efficient removal of heparin from whole blood.
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Alginatos/química , Alginatos/farmacología , Heparina/aislamiento & purificación , Heparina/metabolismo , Membranas Artificiales , Polilisina/análogos & derivados , Absorción/efectos de los fármacos , Animales , Bovinos , Heparina/sangre , Humanos , Concentración de Iones de Hidrógeno , Cinética , Polilisina/química , Polilisina/farmacología , Propiedades de SuperficieRESUMEN
Administration of heparin during extracorporeal procedures increases the risk of haemorrhage. Various reactor designs, including the use of heparinase and poly-L-lysine. HBr hollow fiber, have been investigated for the removal of heparin prior to the blood being returned to the patient; however, none of them have been implemented clinically. In this paper it is proposed that beads made from poly-L-lysine/alginate can be used to remove the heparin. The aim of this work is to perform the necessary experiments in order to get the information required to design a heparin removal reactor that uses these beads. The experiments are aimed at measuring the removal rates of heparin by the beads, testing the efficiency of the beads to remove heparin, determining repeatability and identifying factors that could influence the removal rate. Batch rate experiments using poly-L-lysine/alginate beads in saline solutions were performed to investigate the removal rate of heparin. The results, which indicate that heparin is efficiently removed, may lead to improved bioreactor designs.
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Alginatos/química , Reactores Biológicos , Circulación Extracorporea/instrumentación , Heparina/química , Polilisina/análogos & derivados , Heparina/sangre , Humanos , Microesferas , Polilisina/sangre , Polilisina/químicaRESUMEN
Pulmonary edema has been an unreported finding in the evaluation of abused children. We describe 2 cases of pulmonary edema in abused infants, 1 after confessed suffocation and the other after inflicted head injury. A review of the literature regarding postobstructive and neurogenic pulmonary edema suggests useful inferences for the forensic evaluation of maltreated children who present with this finding.
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Asfixia/complicaciones , Maltrato a los Niños , Edema Pulmonar/diagnóstico , Edema Pulmonar/etiología , Edema Encefálico/complicaciones , Edema Encefálico/diagnóstico , Traumatismos Craneocerebrales/complicaciones , Traumatismos Craneocerebrales/diagnóstico , Urgencias Médicas , Humanos , Lactante , Tiempo de Internación , Pulmón/diagnóstico por imagen , Masculino , Edema Pulmonar/terapia , Radiografía , Respiración Artificial , SucciónRESUMEN
The core particle (CP) of the yeast proteasome is composed of four heptameric rings of subunits arranged in a hollow, barrel-like structure. We have found that the CP is autoinhibited by the N-terminal tails of the outer (alpha) ring subunits. Crystallographic analysis showed that deletion of the tail of the alpha3 subunit opens a channel into the proteolytically active interior chamber of the CP, thus derepressing peptide hydrolysis. In the latent state of the particle, the tails prevent substrate entry by imposing topological closure on the CP. Inhibition by the alpha subunit tails is relieved upon binding of the regulatory particle to the CP to form the proteasome holoenzyme. Opening of the CP channel by assembly of the holoenzyme is regulated by the ATPase domain of Rpt2, one of 17 subunits in the RP. Thus, open-channel mutations in CP subunits suppress the closed-channel phenotype of an rpt2 mutant. These results identify a specific mechanism for allosteric regulation of the CP by the RP.
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Adenosina Trifosfatasas/metabolismo , Secuencias de Aminoácidos/genética , Complejos Multienzimáticos/metabolismo , Péptido Hidrolasas/genética , Péptido Hidrolasas/metabolismo , Complejo de la Endopetidasa Proteasomal , Regulación Alostérica/fisiología , Secuencias de Aminoácidos/fisiología , Cristalografía por Rayos X , Activación Enzimática , Holoenzimas/química , Holoenzimas/genética , Holoenzimas/metabolismo , Humanos , Modelos Moleculares , Complejos Multienzimáticos/química , Complejos Multienzimáticos/genética , Mutagénesis Sitio-Dirigida/genética , Péptido Hidrolasas/química , Subunidades de Proteína , Transporte de Proteínas/fisiología , Alineación de Secuencia , Relación Estructura-Actividad , Levaduras/enzimologíaRESUMEN
BACKGROUND: There are limited data available regarding the cost of care in patients with androgen independent prostate carcinoma (AIPC), and there are no data on the impact of direct nonmedical and indirect costs (DNM/IC). This lack of data, along with the feasibility of collecting DNM/IC, was examined in patients with AIPC who took part in a randomized trial using a newly developed questionnaire, the Collection of Indirect and Nonmedical Direct Costs (COIN) form. METHODS: Patients with AIPC were randomized to one of three treatment arms: 1) strontium only (strontium 4 Mci in Week 1 and Week 12) (STRONT); 2) vinblastine 4 mg/m(2) per week for 3 weeks then 1 week off and estramustine, 10 mg/kg per day (CHEMO); or 3) a combination of treatments outlined in the arms for CHEMO and STRONT (CHEMO/STRONT). Direct medical costs were collected through the hospital billing system. DNM/IC data were obtained prospectively using the COIN form. Cost data were analyzed for a period of 6 months. RESULTS: Twenty-nine patients were randomized, after which the protocol was closed because of poor accrual. The median survival of the patients was 22.3 months. The mean and median total costs for the 20 of 29 patients with complete cost information were $12,647 and $11,257 over 6 months, respectively. DNM/IC represented 11% of the total cost (range, from < 1% to 42%); in 20% of participating individuals, these costs accounted for 35-42% of total costs. Failure to collect complete cost information was due to early death, administrative difficulties, and loss to follow-up. CONCLUSIONS: In this pilot project, the collection of these cost data using the COIN form was feasible and practical and was limited primarily by logistic, not form specific, issues. DNM/IC were found to be a significant proportion of total costs (up to 42%) in selected patients, and this information proved to be a useful addition to the cost analysis. Approximately 98 patients would be required to detect a 20% difference in total costs between arms in a properly powered, randomized trial. Considering the potentially significant impact on total costs, DNM/IC data should be included in future cost-analysis studies of patients with AIPC and other diseases.
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Adenocarcinoma/tratamiento farmacológico , Adenocarcinoma/economía , Antineoplásicos/economía , Antineoplásicos/uso terapéutico , Neoplasias Óseas/tratamiento farmacológico , Neoplasias Óseas/economía , Costo de Enfermedad , Neoplasias de la Próstata/tratamiento farmacológico , Neoplasias de la Próstata/economía , Adenocarcinoma/secundario , Anciano , Neoplasias Óseas/secundario , Costos de los Medicamentos , Estramustina/economía , Estramustina/uso terapéutico , Costos de la Atención en Salud , Gastos en Salud , Costos de Hospital , Humanos , Masculino , Persona de Mediana Edad , Dolor/tratamiento farmacológico , Dolor/economía , Dolor/etiología , Proyectos Piloto , Neoplasias de la Próstata/patología , Estroncio/economía , Estroncio/uso terapéutico , Vinblastina/economía , Vinblastina/uso terapéuticoRESUMEN
The core particle (CP) of the yeast proteasome is composed of four heptameric rings of subunits arranged in a hollow, barrel-like structure. We report that the CP is autoinhibited by the N-terminal tails of the outer (alpha) ring subunits. Crystallographic analysis showed that deletion of the tail of the alpha 3-subunit opens a channel into the proteolytically active interior chamber of the CP, thus derepressing peptide hydrolysis. In the latent state of the particle, the tails prevent substrate entry by imposing topological closure on the CP. Inhibition by the alpha-subunit tails is relieved upon binding of the regulatory particle to the CP to form the proteasome holoenzyme.
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Cisteína Endopeptidasas/química , Cisteína Endopeptidasas/metabolismo , Complejos Multienzimáticos/química , Complejos Multienzimáticos/metabolismo , Saccharomyces cerevisiae/enzimología , Secuencias de Aminoácidos/genética , Secuencia de Aminoácidos , Secuencia Conservada , Cristalografía por Rayos X , Cisteína Endopeptidasas/genética , Holoenzimas/química , Holoenzimas/genética , Holoenzimas/metabolismo , Humanos , Hidrólisis , Modelos Moleculares , Datos de Secuencia Molecular , Complejos Multienzimáticos/antagonistas & inhibidores , Complejos Multienzimáticos/genética , Mutación/genética , Fragmentos de Péptidos/química , Fragmentos de Péptidos/genética , Fragmentos de Péptidos/metabolismo , Complejo de la Endopetidasa Proteasomal , Estructura Cuaternaria de Proteína , Subunidades de Proteína , Saccharomyces cerevisiae/genética , Alineación de Secuencia , Relación Estructura-ActividadRESUMEN
The 26S proteasome is a multi-subunit ATP-dependent protease responsible for degrading most short-lived intracellular proteins targeted for breakdown by ubiquitin conjugation. The complex is composed of two relatively stable subparticles, the 20S proteasome, a hollow cylindrical structure which contains the proteolytic active sites in its lumen, and the 19S regulatory particle (RP) which binds to either end of the cylinder and provides the ATP-dependence and the specificity for ubiquitinated proteins. Among the approximately 18 subunits of the RP from yeast and animals are a set of six proteins, designated RPT1-6 for regulatory particle triple-A ATPase, that form a distinct family within the AAA superfamily. Presumably, these subunits use ATP hydrolysis to help assemble the 26S holocomplex, recognize and unfold appropriate substrates, and/or translocate the substrates to the 20S complex for degradation. Here, we describe the RPT gene family from Arabidopsis thaliana. From a collection of cDNAs and genomic sequences, a family of genes encoding all six of the RPT subunits was identified with significant amino acid sequence similarity to their yeast and animal counterparts. Five of the six RPT sub- units are encoded by two genes; the exception being RPT3 which is encoded by a single gene. mRNA for each of the six proteins is present in all tissue types examined. Five of the subunits (RPT1 and 3-6) complemented yeast mutants missing their respective orthologs, indicating that the yeast and Arabidopsis proteins are functionally equivalent. Taken together, these results demonstrate that the RP, like the 20S proteasome, is functionally and structurally conserved among eukaryotes and indicate that the plant RPT subunits, like their yeast counterparts, have non-redundant functions.
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Adenosina Trifosfatasas/genética , Arabidopsis/genética , Genes de Plantas , Familia de Multigenes , Péptido Hidrolasas/genética , Complejo de la Endopetidasa Proteasomal , Secuencia de Aminoácidos , Arabidopsis/enzimología , Arabidopsis/efectos de la radiación , Evolución Molecular , Prueba de Complementación Genética , Genoma de Planta , Luz , Datos de Secuencia Molecular , Homología de Secuencia de Aminoácido , Distribución Tisular , Levaduras/genéticaRESUMEN
We have developed S. cerevisiae as a model system for mechanistic studies of the 26S proteasome. The subunits of the yeast 19S complex, or regulatory particle (RP), have been defined, and are closely related to those of mammalian proteasomes. The multiubiquitin chain binding subunit (S5a/Mcb1/Rpn10) was found, surprisingly, to be nonessential for the degradation of a variety of ubiquitin-protein conjugates in vivo. Biochemical studies of proteasomes from deltarpn10 mutants revealed the existence of two structural subassemblies within the RP, the lid and the base. The lid and the base are both composed of 8 subunits. By electron microscopy, the base and the lid correspond to the proximal and distal masses of the RP, respectively. The base is sufficient to activate the 20S core particle for degradation of peptides, but the lid is required for ubiquitin-dependent degradation. The lid subunits share sequence motifs with components of the COP9/signalosome complex, suggesting that these functionally diverse particles have a common evolutionary ancestry. Analysis of equivalent point mutations in the six ATPases of the base indicate that they have well-differentiated functions. In particular, mutations in one ATPase gene, RPT2, result in an unexpected defect in peptide hydrolysis by the core particle. One interpretation of this result is that Rpt2 participates in gating of the channel through which substrates enter the core particle.
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Adenosina Trifosfatasas/metabolismo , Cisteína Endopeptidasas/metabolismo , Complejos Multienzimáticos/metabolismo , Saccharomyces cerevisiae/enzimología , Adenosina Trifosfatasas/química , Animales , Cisteína Endopeptidasas/química , Humanos , Complejos Multienzimáticos/química , Complejo de la Endopetidasa Proteasomal , Proteínas/metabolismo , Saccharomyces cerevisiae/química , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae , Ubiquitinas/metabolismoRESUMEN
A family of ATPases resides within the regulatory particle of the proteasome. These proteins (Rpt1-Rpt6) have been proposed to mediate substrate unfolding, which may be required for translocation of substrates through the channel that leads from the regulatory particle into the proteolytic core particle. To analyze the role of ATP hydrolysis in protein breakdown at the level of the individual ATPase, we have introduced equivalent site-directed mutations into the ATPbinding motif of each RPT gene. Non-conservative substitutions of the active-site lysine were lethal in four of six cases, and conferred a strong growth defect in two cases. Thus, the ATPases are not functionally redundant, despite their multiplicity and sequence similarity. Degradation of a specific substrate can be inhibited by ATP-binding-site substitutions in many of the Rpt proteins, indicating that they co-operate in the degradation of individual substrates. The phenotypic defects of the different rpt mutants were strikingly varied. The most divergent phenotype was that of the rpt1 mutant, which was strongly growth defective despite showing no general defect in protein turnover. In addition, rpt1 was unique among the rpt mutants in displaying a G1 cell-cycle defect. Proteasomes purified from an rpt2 mutant showed a dramatic inhibition of peptidase activity, suggesting a defect in gating of the proteasome channel. In summary, ATP promotes protein breakdown by the proteasome through multiple mechanisms, as reflected by the diverse phenotypes of the rpt mutants.
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Adenosina Trifosfatasas/metabolismo , Adenosina Trifosfato/metabolismo , Cisteína Endopeptidasas/metabolismo , Complejos Multienzimáticos/metabolismo , Adenosina Trifosfatasas/genética , Sitios de Unión/genética , Cisteína Endopeptidasas/química , Cisteína Endopeptidasas/genética , Hidrólisis , Complejos Multienzimáticos/química , Complejos Multienzimáticos/genética , Mutagénesis Sitio-Dirigida , Complejo de la Endopetidasa Proteasomal , Proteínas/metabolismo , Alineación de Secuencia , Supresión Genética , Levaduras/enzimología , Levaduras/genéticaRESUMEN
The proteasome consists of a 20S proteolytic core particle (CP) and a 19S regulatory particle (RP), which selects ubiquitinated substrates for translocation into the CP. An eight-subunit subcomplex of the RP, the lid, can be dissociated from proteasomes prepared from a deletion mutant for Rpn10, an RP subunit. A second subcomplex, the base, contains all six proteasomal ATPases and links the RP to the CP. The base is sufficient to activate the CP for degradation of peptides or a nonubiquitinated protein, whereas the lid is required for ubiquitin-dependent degradation. By electron microscopy, the base and the lid correspond to the proximal and distal masses of the RP, respectively. The lid subunits share sequence motifs with components of the COP9/signalosome complex and eIF3, suggesting that these functionally diverse particles have a common evolutionary ancestry.
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Cisteína Endopeptidasas/química , Cisteína Endopeptidasas/fisiología , Proteínas de Unión al ADN , Complejos Multienzimáticos/química , Complejos Multienzimáticos/fisiología , Proteínas de Plantas/fisiología , Proteínas , Proteínas Proto-Oncogénicas/fisiología , Factores de Transcripción/fisiología , Ubiquitinas/metabolismo , Complejo del Señalosoma COP9 , Proteínas Portadoras/fisiología , Cisteína Endopeptidasas/ultraestructura , Proteínas Fúngicas/química , Proteínas Fúngicas/fisiología , Proteínas Fúngicas/ultraestructura , Microscopía Electrónica , Complejos Multienzimáticos/ultraestructura , Complejos Multiproteicos , Péptido Hidrolasas , Complejo de la Endopetidasa Proteasomal , Proteínas Proto-Oncogénicas c-ets , Saccharomyces cerevisiae , Proteínas de Saccharomyces cerevisiae , Homología de Secuencia de Aminoácido , Transducción de Señal/fisiología , Ubiquitinas/fisiologíaAsunto(s)
Cisteína Endopeptidasas/química , Complejos Multienzimáticos/química , Saccharomyces cerevisiae/enzimología , Animales , Cisteína Endopeptidasas/genética , Humanos , Complejos Multienzimáticos/genética , Complejo de la Endopetidasa Proteasomal , Conformación Proteica , Saccharomyces cerevisiae/genética , Terminología como AsuntoRESUMEN
The proteasome is a multisubunit protease responsible for degrading proteins conjugated to ubiquitin. The 670-kDa core particle of the proteasome contains the proteolytic active sites, which face an interior chamber within the particle and are thus protected from the cytoplasm. The entry of substrates into this chamber is thought to be governed by the regulatory particle of the proteasome, which covers the presumed channels leading into the interior of the core particle. We have resolved native yeast proteasomes into two electrophoretic variants and have shown that these represent core particles capped with one or two regulatory particles. To determine the subunit composition of the regulatory particle, yeast proteasomes were purified and analyzed by gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Resolution of the individual polypeptides revealed 17 distinct proteins, whose identities were determined by amino acid sequence analysis. Six of the subunits have sequence features of ATPases (Rpt1 to Rpt6). Affinity chromatography was used to purify regulatory particles from various strains, each of which expressed one of the ATPases tagged with hexahistidine. In all cases, multiple untagged ATPases copurified, indicating that the ATPases assembled together into a heteromeric complex. Of the remaining 11 subunits that we have identified (Rpn1 to Rpn3 and Rpn5 to Rpn12), 8 are encoded by previously described genes and 3 are encoded by genes not previously characterized for yeasts. One of the previously unidentified subunits exhibits limited sequence similarity with deubiquitinating enzymes. Overall, regulatory particles from yeasts and mammals are remarkably similar, suggesting that the specific mechanistic features of the proteasome have been closely conserved over the course of evolution.
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Cisteína Endopeptidasas/química , Endopeptidasas , Complejos Multienzimáticos/química , Saccharomyces cerevisiae/enzimología , Secuencia de Aminoácidos , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Cromatografía de Afinidad , Cisteína Endopeptidasas/genética , Cisteína Endopeptidasas/metabolismo , ADN de Hongos/química , Biblioteca de Genes , Datos de Secuencia Molecular , Peso Molecular , Complejos Multienzimáticos/genética , Complejos Multienzimáticos/metabolismo , Mapeo Peptídico , Complejo de la Endopetidasa Proteasomal/genética , Complejo de la Endopetidasa Proteasomal/metabolismo , Conformación Proteica , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Alineación de Secuencia , Relación Estructura-ActividadRESUMEN
The 26 S proteasome is a multisubunit proteolytic complex responsible for degrading eukaryotic proteins targeted by ubiquitin modification. Substrate recognition by the complex is presumed to be mediated by one or more common receptor(s) with affinity for multiubiquitin chains, especially those internally linked through lysine 48. We have identified previously a candidate for one such receptor from diverse species, designated here as Mcb1 for Multiubiquitin chain-binding protein, based on its ability to bind Lys48-linked multiubiquitin chains and its location within the 26 S proteasome complex. Even though Mcb1 is likely not the only receptor in yeast, it is necessary for conferring resistance to amino acid analogs and for degrading a subset of ubiquitin pathway substrates such as ubiquitin-Pro-beta-galactosidase (Ub-Pro-beta-gal) (van Nocker, S., Sadis, S., Rubin, D.M., Glickman, M., Fu, H., Coux, O., Wefes, I., Finley, D., and Vierstra, R. D. (1996) Mol. Cell. Biol. 16, 6020-28). To further define the role of Mcb1 in substrate recognition by the 26 S proteasome, a structure/function analysis of various deletion and site-directed mutants of yeast and Arabidopsis Mcb1 was performed. From these studies, we identified a single stretch of conserved hydrophobic amino acids (LAM/LALRL/V (ScMcb1 228-234 and At-Mcb1 226-232)) within the C-terminal half of each polypeptide that is necessary for interaction with Lys48-linked multiubiquitin chains. Unexpectedly, this domain was not essential for either Ub-Pro-beta-gal degradation or conferring resistance to amino acid analogs. The domain responsible for these two activities was mapped to a conserved region near the N terminus. Yeast and Arabidopsis Mcb1 derivatives containing an intact multiubiquitin-binding site but missing the N-terminal region failed to promote Ub-Pro-beta-gal degradation and even accentuated the sensitivity of the yeast delta mcb1 strain to amino acid analogs. This hypersensitivity was not caused by a gross defect in 26 S proteasome assembly as mutants missing either the N-terminal domain or the multiubiquitin chain-binding site could still associate with 26 S proteasome and generate a complex indistinguishable in size from that present in wild-type yeast. Together, these data indicate that residues near the N terminus, and not the multiubiquitin chain-binding site, are most critical for Mcb1 function in vivo.
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Proteínas de Arabidopsis , Proteínas Portadoras/química , Péptido Hidrolasas/química , Complejo de la Endopetidasa Proteasomal , Secuencia de Aminoácidos , Animales , Arabidopsis , Secuencia de Bases , Sitios de Unión , Proteínas Portadoras/genética , Secuencia de Consenso , Análisis Mutacional de ADN , Cartilla de ADN , Drosophila , Proteínas Fúngicas/química , Proteínas Fúngicas/genética , Humanos , Datos de Secuencia Molecular , Reacción en Cadena de la Polimerasa , LevadurasRESUMEN
The 26S proteasome is a 2-Megadalton proteolytic complex with over 30 distinct subunits. The 19S particle, a subcomplex of the 26S proteasome, is thought to confer ATP-dependence and ubiquitin-dependence on the proteolytic core particle of the proteasome. Given the complexity of the 19S particle, genetic approaches are likely to play an important role in its analysis. We have initiated biochemical and genetic studies of the 19S particle in Saccharomyces cerevisiae. Here we describe the localization to the proteasome of several ATPases that were previously proposed to be involved in transcription. Independent studies indicate that the mammalian 26S proteasome contains closely related ATPases. We have also found that the multiubiquitin chain binding protein Mcb1, a homolog of the mammalian S5a protein, is a subunit of the yeast proteasome. However, contrary to expectation, MCB1 is not an essential gene in yeast. The mcb1 mutant grows at a nearly wild-type rate, and the breakdown of most ubiquitin-protein conjugates is unaffected in this strain. One substrate, Ub-Proline-beta gal, was found to require MCB1 for its breakdown, but it remains unclear whether Mcb1 serves as a ubiquitin receptor in this process. Our data suggest that the recognition of ubiquitin conjugates by the proteasome is a complex process which must involve proteins other than Mcb1.