RESUMEN
This paper presents the first plasmid DNA irradiations carried out with Very High Energy Electrons (VHEE) over 100-200 MeV at the CLEAR user facility at CERN to determine the Relative Biological Effectiveness (RBE) of VHEE. DNA damage yields were measured in dry and aqueous environments to determine that ~ 99% of total DNA breaks were caused by indirect effects, consistent with other published measurements for protons and photons. Double-Strand Break (DSB) yield was used as the biological endpoint for RBE calculation, with values found to be consistent with established radiotherapy modalities. Similarities in physical damage between VHEE and conventional modalities gives confidence that biological effects of VHEE will also be similar-key for clinical implementation. Damage yields were used as a baseline for track structure simulations of VHEE plasmid irradiation using GEANT4-DNA. Current models for DSB yield have shown reasonable agreement with experimental values. The growing interest in FLASH radiotherapy motivated a study into DSB yield variation with dose rate following VHEE irradiation. No significant variations were observed between conventional and FLASH dose rate irradiations, indicating that no FLASH effect is seen under these conditions.
Asunto(s)
Partículas beta , Roturas del ADN de Doble Cadena , Modelos Químicos , Plásmidos/químicaRESUMEN
Epitaxial ultrathin titanium dioxide films of 0.3 to approximately 7 nm thickness on a metal single crystal substrate have been investigated by high resolution vibrational and electron spectroscopies. The data complement previous morphological data provided by scanned probe microscopy and low energy electron diffraction to provide very complete characterization of this system. The thicker films display electronic structure consistent with a stoichiometric TiO(2) phase. The thinner films appear nonstoichiometric due to band bending and charge transfer from the metal substrate, while work function measurements also show a marked thickness dependence. The vibrational spectroscopy shows three clear phonon bands at 368, 438, and 829 cm(-1) (at 273 K), which confirms a rutile structure. The phonon band intensity scales linearly with film thickness and shift slightly to lower frequencies with increasing temperature, in accord with results for single crystals.
RESUMEN
Treatment of acylnitroso hetero Diels-Alder cycloadducts 2 with iron(III) or copper(II) in an alcohol solvent induces ring opening to afford predominantly monocyclic anti-1,4-hydroxamic acids 3. However, treatment of cycloadducts 2 with copper(II) in toluene reverses the stereoselectivity of the ring opening to afford syn-1,4-hydroxamic acids 4. These regio- and stereoselective processes separately provide anti-1,4- and syn-1,4-disubstituted cyclopentenes while regenerating a hydroxamic acid moiety, thus enhancing the chemical versatility of the Diels-Alder cycloadducts.
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Cicloparafinas/química , Ácidos Hidroxámicos/síntesis química , Compuestos Nitrosos/química , Cobre/química , Compuestos Férricos/química , EstereoisomerismoRESUMEN
[reaction: see text] A conformationally restricted analogue (5) of N(omega)-acetyl-N(omega)-hydroxyornithine and -lysine was synthesized. The synthesis features an efficient acylnitroso hetero-Diels-Alder cycloadduct (1) ring opening with palladium(0) and methylnitroacetate.
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Lisina/síntesis química , Ornitina/síntesis química , Oxo-Ácido-Liasas/metabolismo , Sideróforos/metabolismo , Catálisis , Lisina/análogos & derivados , Lisina/química , Estructura Molecular , Ornitina/análogos & derivados , Ornitina/química , Paladio/química , Relación Estructura-Actividad , Especificidad por SustratoRESUMEN
Tapasin mediates the binding of MHC class I molecules to the transporter associated with antigen processing (TAP). Deletion mutants of tapasin were used to examine the effect of tapasin on interactions within the MHC class I complex. Binding to TAP is mediated by the C-terminal region of tapasin. Michaelis-Menten analysis of peptide transport shows that this interaction is sufficient to increase TAP levels without significantly affecting the intrinsic translocation rate. Weak interactions exist between MHC class I molecules and TAP in the absence of tapasin, and between free heavy chains and TAP-tapasin complexes in the absence of beta2-microglobulin. The N-terminal 50 residues of tapasin constitute the key element which converts the sum of these weak interactions into a stable complex.
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Antiportadores/química , Antiportadores/metabolismo , Antígenos de Histocompatibilidad Clase I/metabolismo , Inmunoglobulinas/química , Inmunoglobulinas/metabolismo , Transportador de Casetes de Unión a ATP, Subfamilia B, Miembro 2 , Transportadoras de Casetes de Unión a ATP/metabolismo , Presentación de Antígeno , Antiportadores/genética , Secuencia de Bases , Sitios de Unión/genética , Transporte Biológico Activo , Proteínas de Unión al Calcio/metabolismo , Calreticulina , Línea Celular , Cartilla de ADN/genética , Estabilidad de Medicamentos , Proteínas de Choque Térmico/metabolismo , Humanos , Inmunoglobulinas/genética , Isomerasas/metabolismo , Cinética , Sustancias Macromoleculares , Proteínas de Transporte de Membrana , Chaperonas Moleculares/metabolismo , Unión Proteica , Proteína Disulfuro Isomerasas , Ribonucleoproteínas/metabolismo , Microglobulina beta-2/metabolismoRESUMEN
Tapasin forms a bridge between TAP (transporters associated with antigen processing) and MHC class I molecules and plays a critical role in class I assembly. In its absence, TAP and class I do not associate, and class I cell surface expression is reduced. We now identify two independent functions for tapasin. Tapasin increases TAP levels and allows more peptide to be translocated to the endoplasmic reticulum. Furthermore, when expressed in the tapasin-negative .220 cell line, recombinant soluble tapasin retains its association with class I and restores class I cell surface expression and function, even though it no longer binds TAP or increases TAP levels. This finding suggests that the association of tapasin with class I is sufficient to facilitate loading and assembly of class I molecules.
Asunto(s)
Transportadoras de Casetes de Unión a ATP/metabolismo , Presentación de Antígeno , Antiportadores/metabolismo , Antígeno HLA-B8/metabolismo , Inmunoglobulinas/metabolismo , Péptidos/metabolismo , Transportador de Casetes de Unión a ATP, Subfamilia B, Miembro 2 , Miembro 3 de la Subfamilia B de Transportadores de Casetes de Unión a ATP , Antiportadores/genética , Transporte Biológico , Retículo Endoplásmico/metabolismo , Humanos , Inmunoglobulinas/genética , Proteínas de Transporte de Membrana , Mutación , Unión Proteica , Solubilidad , Linfocitos T Citotóxicos/inmunologíaRESUMEN
HLA-DM is a major histocompatibility complex (MHC) class II-like molecule that facilitates antigen processing by catalyzing the exchange of invariant chain-derived peptides (CLIP) from class II molecules for antigenic peptides. HLA-DO is a second class II-like molecule that physically associates with HLA-DM in B cells. HLA-DO was shown to block HLA-DM function. Purified HLA-DM-DO complexes could not promote peptide exchange in vitro. Expression of HLA-DO in a class II+ and DM+, DO- human T cell line caused the accumulation of class II-CLIP complexes, indicating that HLA-DO blocked DM function in vivo and suggesting that HLA-DO is an important modulator of class II-restricted antigen processing.
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Presentación de Antígeno , Linfocitos B/inmunología , Antígenos HLA-D/metabolismo , Proteínas Nucleares , Linfocitos T/inmunología , Secuencia de Aminoácidos , Antígenos de Diferenciación de Linfocitos B/metabolismo , Antígeno HLA-DR3/metabolismo , Antígenos de Histocompatibilidad Clase II/metabolismo , Humanos , Datos de Secuencia Molecular , Transactivadores/genética , Transfección , Células Tumorales CultivadasRESUMEN
N-acetyl-L-leucyl-L-leucyl-L-norleucinal, (LLnL), which inhibits proteasomes in addition to other proteases, was found to prolong the association of major histocompatibility complex class I molecules with the transporters associated with antigen processing (TAP), and to slow their transport out of the endoplasmic reticulum (ER). LLnL induced a reversible accumulation of ubiquitinated proteins and changed the spectrum of peptides bound by class I molecules. These effects can probably be attributed to proteasome inhibition. Unexpectedly, in the TAP-deficient cell line .174, the rate of intracellular transport of human histocompatibility leukocyte antigen (HLA) A2 was also reduced by LLnL, and the generation of most HLA-A2-associated signal sequence peptides was inhibited. The inhibition of HLA-A2 transport in .174 cells was found to be less sensitive to LLnL than in wild-type cells, and a similar difference was found for a second protease inhibitor, benzyloxycarbonyl-L-leucyl-L-leucyl-L-phenylalanilal. These data suggest that under some conditions such inhibitors can block trimming of peptides by an ER peptidase in addition to inhibiting cytosolic peptide generation.
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Inhibidores de Cisteína Proteinasa/farmacología , Retículo Endoplásmico/metabolismo , Antígenos de Histocompatibilidad Clase I/metabolismo , Leupeptinas/farmacología , Péptidos/metabolismo , Secuencia de Aminoácidos , Transporte Biológico , Proteínas Portadoras/metabolismo , Compartimento Celular , Citosol/efectos de los fármacos , Datos de Secuencia Molecular , Oligopéptidos/farmacología , Unión ProteicaRESUMEN
Hyperbaric oxygen therapy, a controversial field of medicine that is not yet well understood, is the use of pressurization to deliver increased oxygen concentrations to the body and in particular to increase the amount of oxygen diffused in the plasma. This article is intended to provide ET nurses with an introduction to the physics of hyperbaric oxygen therapy and to illustrate how this therapy may be beneficial in aiding healing in selected patients. Methods of oxygen delivery, a review of the physics of hyperbaric oxygen therapy, including a brief explanation of the gas laws pertinent to hyperbaric oxygen therapy, and clinical considerations (clinical effects, implications, indications, contraindications, assessment parameters, treatment protocols, risks, side effects, and wound dressings suitable for this specialized environment) are discussed. Approved indications for hyperbaric oxygen therapy and contact information for locating the nearest hyperbaric oxygen therapy facility are included.
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Oxigenoterapia Hiperbárica/métodos , Vendajes , Contraindicaciones , Enterostomía/enfermería , Humanos , Oxigenoterapia Hiperbárica/enfermería , Enfermeras Clínicas , Evaluación en EnfermeríaRESUMEN
The invariant chain, which associates with the major histocompatibility complex (MHC) class II molecules in the endoplasmic reticulum, serves two functions important in antigen processing. First, it prevents class II molecules from binding peptides in the early stages of intracellular transport. Second, it contains a cytoplasmic signal that targets the class II-invariant chain complex to an acidic endosomal compartment. Proteolytic cleavage and subsequent dissociation of the invariant chain then occurs, allowing peptides derived from endocytosed proteins to bind to released class II molecules before their expression at the cell surface. Certain human cell lines that are mutant in one or more MHC-linked genes are defective in class II-restricted antigen processing. Here we show that in transfectants of one of these cell lines, T2, this deficiency results in the association of a large proportion of class II molecules with a nested set of invariant-chain-derived peptides (class II-associated invariant chain peptides, or CLIP). HLA-DR3 molecules isolated from T2 transfectants can be efficiently loaded with antigenic peptides by exposure to a low pH in vitro, perhaps reflecting the in vivo conditions in which peptides associate with class II molecules. Addition of synthetic CLIP inhibits the loading process, indicating that CLIP may define the region of the invariant chain responsible for obstructing the class II binding site.