Resumen: Accessory minerals are thought to play a key role in controlling the behaviour of certain trace elements such as REE, Y, Zr,
Th and U during crustal melting processes under high-grade metamorphic conditions. Although this is probably the case at
middle crustal levels, when a comparison is made with granulite-facies lower crustal
levels, differences are seen in trace element
behaviour between accessory minerals and some major phases. Such a comparison can be made in Central Spain where two
granulite-facies terranes have equilibrated under slightly different metamorphic conditions and where lower crustal xenoliths are
also found. Differences in texture and chemical composition between accessory phases found in leucosomes and leucogranites
and those of melanosomes and protholiths indicate that most of the accessory minerals in melt-rich migmatites are newly
crystallized. This implies that an important redistribution of trace elements occurs during the early stages of granulite-facies
metamorphism. In addition, the textural position of the accessory minerals with respect to the major phases is crucial in the
redistribution of trace elements when melting proceeds via biotite dehydration melting reactions. In granulitic xenoliths from
lower crustal levels, the situation seems to be different, as major minerals show high concentration of certain trace elements, the
distribution of which is thus controlled by reactions involving final consumption of Al-Ti-phlogopite. A marked redistribution
of HREE–Y–Zr between garnet and xenotime (where present) and zircon, but also of LREE between feldspars (K-feldspar and
plagioclase) and monazite, is suggested.
Resumen: Knowledge of the evolution of Spanish fluvial networks has improved during recent years as more river systems have been studied and
more geochronological data has become available. However, the chronological framework is a major issue as the range of applications is
limited by methodological constraints and spatial coverage is sparse. Integration of ‘absolute’ dating methods with
biostratigraphy and
palaeomagnetism permits the recent evolution of these river systems to be reviewed. The timing of incision from the Late Neogene to the
present varies between the major Iberian fluvial systems, depending on the substrata and tectonic settings. Early Pleistocene and older
fluvial sequences in the core areas of the Iberian Peninsula provide a more extensive record of fluvial evolution and are better preserved
than the terrace flights in the coastal lowlands. Middle Pleistocene sequences are well developed in most of the major river systems in
Iberia, particularly those of the Tajo, Guadalquivir and Aguas River, and frequently represent the principal climatic cycles of that
period, although tectonic and sea-level effects can also be seen. For Late Pleistocene to Holocene times, the scheme becomes more
complex. Our review suggests that each river system has responded differently to local and regional climate control, glacial and
periglacial processes in headwaters in high mountain areas, glacio-eustatic sea-level changes and local and regional tectonic patterns.
Resumen: There is a significant enrichment in some trace elements in the major residual minerals of peraluminous granulite xenoliths from
the lower crust. Those trace elements are released from the breakdown of accessory phases at high-T granulite-facies conditions
(N850 °C). Around 10–35% of Zr is hosted in granulite rutile and garnet, whereas, the entire LREE–Eu
budget is controlled by
feldspar. The Zr- and REE-compatible behaviour of the major granulite phases, combined with the scarcity of accessory phases,
which are mostly included in major granulite minerals, leads to a disequilibrium in accessory dissolution in the peraluminous
partial melts. Thus the melt extracts less Zr and LREE and, consequently, generates the false impression of having lower-T when
applying current accessory phase dissolution models.
Resumen: We introduced previously an on-line resource, RANKPEP that uses position specific scoring matrices (PSSMs) or profiles for the prediction of peptide-MHC class I (MHCI) binding as a basis for CD8 T-cell epitope identification. Here, using PSSMs that are structurally consistent with the binding mode of MHC class II (MHCII) ligands, we have extended RANKPEP to prediction
of peptide-MHCII binding and anticipation of CD4 T-cell epitopes. Currently, 88 and 50 different MHCI and MHCII molecules, respectively, can be targeted for peptide binding predictions in RANKPEP. Because appropriate processing of antigenic peptides must occur prior to major histocompatibility complex (MHC) binding, cleavage site prediction methods are important adjuncts for T-cell epitope discovery. Given that the C-terminus of most MHCI-restricted epitopes results from proteasomal cleavage, we have modeled the cleavage site from known MHCI-restricted epitopes using statistical language models. The RANKPEP server now determines whether the C-terminus of any predicted MHCI ligand may result from such proteasomal cleavage. Also implemented is a variability masking function. This feature focuses prediction on conserved rather than highly variable protein segments encoded by infectious genomes, thereby offering identification of invariant T-cell epitopes to thwart mutation as an immune evasion mechanism.
Palabras clave: Epitopes; Major histocompatibility complex; Prediction; Profile; Proteasome
Resumen: Plate convergence analysis in collisional orogens is usually based on the study of major contractional structures and
strike-slip shear zones. Here we show how the structural analysis of extensional structures may report the regional
or far stress field during relatively local, gravity-driven extensional collapse of a thickened continental
crust and how
this information may be used to constrain the broad vectors of plate convergence at that time. The Padro´n migmatitic
dome is a synconvergent extensional system developed in the axial zone of the Variscan belt exposed in the NW part
of the Iberian Massif of Spain. This system affected the allochthonous and autochthonous sequences involved in
Pangaea’s assembly in Southern Europe. It includes three major extensional shear zones, which have been analyzed
in detail to provide a wide ground data set for the discussion of the proposed model. The tectonic flow in the Padrón
migmatitic dome and in other coeval structures is characterized by vectors ranging from parallel to oblique, in the
latter case with a counterclockwise azimuth in relation to the trend of the orogenic belt. Our model suggests that
the extensional collapse of the Variscan belt inNWIberia would have developed if the convergence between Gondwana
and Laurussia had not stopped and that it would have included a dextral component.
Resumen: The Permian alkaline lamprophyres from the Spanish Central System (SCS) are highly porphyritic rocks which carry
a heterogeneous population of clinopyroxene and kaersutite zoned phernocrysts. Clinopyroxene phenocrysts may show 1) normal
zoning (Cpx-I), 2) reverse zoning with Fe-rich green cores (Cpx-II), and 3) reverse zoning with colourless Al-poor,
silica-rich cores
(Cpx-III). Kaersutite phenocrysts also show a slight reverse zoning. Major and trace element composition of Cpx-I suggests that
their compositional variation is related to a crystal fractionation process from melts similar to the host lamprophyres. The Cpx-II
cores represent crystallization from highly evolved melts (low Mg-Cr contents and incompatible element enrichment), genetically
related with the SCS alkaline magmatism, and the growth or surrounding Mg-rich inner rims points to a magma mixing process.
The major and trace element composition of Cpx-III cores supports derivation from a magma which has fractionated plagioclase.
This characteristic, together with their similarities when compared to clinopyroxenes from charnockite xenoliths, suggests that
they might be xenocrysts from deep calc-alkaline cumulates. The composition of melts in equilibrium with clinopyroxene and
amphibole phenocrysts supports a model in which Cpx-II and Cpx-III cores would have been incorporated into a more primitive
lamprophyric magma stagnated at lower crustal levels. The low pressure composition of all phenocryst outer rims indicates that
they crystallised directly from the host alkaline magma at their subvolcanic emplacement levels.
Resumen: The MTX-resistant Leishmania major promastigote cell line D7BR1000 displays extrachromosomal amplified R-region DNA, which contains the gene for dihydrofolate reductase-thymidylate synthase (DHFR-TS) (Garvey, E. P., and Santi, D. V. (1986) Science 233, 535-540). Now we report that these methotrexate (MTX)-resistant cells also
possessed a structurally altered DHFR-TS. We have performed the cloning, expression, and characterization of the altered DHFR-TS gene. The DNA sequence of the altered DHFR-TS gene revealed a single base change in position 158 which resulted in the substitution of a methionine in position 53 of DHFR for an arginine. Steady-state measurements of the purified recombinant enzyme indicated that the mutation did not cause significant modifications in the Km for DHFR or TS substrates but lowered the kcat by 4-fold. Of greater interest, there was a modification in the effect on MTX inhibition of DHFR. The initial inhibition complex appeared to have been unaffected by the alteration, but the subsequent slow-binding step of inhibition in the wild-type enzyme is absent in the altered enzyme. Consequently, the overall Ki for MTX was 30-fold greater for the mutant than for the wild-type enzyme. Transfection of L. major with the mutant DHFR-TS gene gives parasites that are capable of growing in medium containing 10 mM methotrexate, showing that the altered DHFR gene is in itself capable of conferring MTX resistance in Leishmania.
Resumen: The MTX-resistant Leishmania major promastigote cell line D7BR1000 displays extrachromosomal amplified R-region DNA, which contains the gene for dihydrofolate reductase-thymidylate synthase (DHFR-TS) (Garvey, E. P., and Santi, D. V. (1986) Science 233, 535-540). Now we report that these methotrexate (MTX)-resistant
cells also possessed a structurally altered DHFR-TS. We have performed the cloning, expression, and characterization of the altered DHFR-TS gene. The DNA sequence of the altered DHFR-TS gene revealed a single base change in position 158 which resulted in the substitution of a methionine in position 53 of DHFR for an arginine. Steady-state measurements of the purified recombinant enzyme indicated that the mutation did not cause significant modifications in the Km for DHFR or TS substrates but lowered the kcat by 4-fold. Of greater interest, there was a modification in the effect on MTX inhibition of DHFR. The initial inhibition complex appeared to have been unaffected by the alteration, but the subsequent slow-binding step of inhibition in the wild-type enzyme is absent in the altered enzyme. Consequently, the overall Ki for MTX was 30-fold greater for the mutant than for the wild-type enzyme. Transfection of L. major with the mutant DHFR-TS gene gives parasites that are capable of growing in medium containing 10 mM methotrexate, showing that the altered DHFR gene is in itself capable of conferring MTX resistance in Leishmania.
