Descripción: Nitrous acid degradation of heparin followed by high-performance anion-exchange chromatography (HPAEC) separation and ultraviolet matrix assisted laser desorption/ionization time-of-flight (UV-MALDI-TOF) analysis led to the structural determination of six sulfated oligosaccharides. Three different matrices (α-cyano-4-hydroxycinnamic acid (CHCA), nor-harmane, and dihydroxybenzoic acid (DHB)) have been used, and the complementary results obtained allowed in most cases to assign the position of sulfate groups. Based on the different cleavages produced on the purified oligosaccharides in source during the MS analysis by the use of the different matrices, this approach provides a new tool for structural analysis. © 2010 American Society for Mass Spectrometry.

Descripción: The geomorphologic analysis of the study area led to distinguish some formations not considered in previous geological research, as well as to explain the characteristics of the present relief. Thirteen principal geomorphic units produced by different geomorphic processes are recognized. Their variety and incidence through the time are expressed in the glacial morphogenesis concentrated in the western part of the Cordillera del Viento, in the volcanic landscape that predominates in the northern and eastern sectors (calderas, volcanoes, lava flows), in the structural control that defines the morphology of the fluvial process in the central zone and a firstly recognized important landslide to the north of Tricao Malal. As a result of the methodology employed two geological units of different age in the western part of the Tromen-Waile volcanic field were distinguished, which were initially interpreted as a single formation. A limited but consistent structural analysis of the region is also included.

Descripción: The addition of Grignard reagents to aldehydes in the presence of chiral aminoal-cohols shows a moderate enantioselectivity. The study carried out with a series of ligands allows the correlation between the structural characteristics and their reactivity.

Descripción: Riboflavin, an essential cofactor for all organisms, is biosynthesized in plants, fungi and microorganisms. The penultimate step in the pathway is catalyzed by the enzyme lumazine synthase. One of the most distinctive characteristics of this enzyme is that it is found in different species in two different quaternary structures, pentameric and icosahedral, built from practically the same structural monomeric unit. In fact, the icosahedral structure is best described as a capsid of twelve pentamers. Despite this noticeable difference, the active sites are virtually identical in all structurally studied members. Furthermore, the main regions involved in the catalysis are located at the interface between adjacent subunits in the pentamer. Thus, the two quaternary forms of the enzyme must meet similar structural requirements to achieve their function, but, at the same time, they should differ in the sequence traits responsible for the different quaternary structures observed. Here, we present a combined analysis that includes sequence-structure and evolutionary studies to find the sequence determinants of the different quaternary assemblies of this enzyme. A data set containing 86 sequences of the lumazine synthase family was recovered by sequence similarity searches. Seven of them had resolved three-dimensional structures. A subsequent phylogenetic reconstruction by maximum parsimony (MP) allowed division of the total set into two clusters in accord with their quaternary structure. The comparison between the patterns of three-dimensional contacts derived from the known three-dimensional structures and variation in sequence conservation revealed a significant shift in structural constraints of certain positions. Also, to explore the changes in functional constraints between the two groups, site-specific evolutionary rate shifts were analyzed. We found that the positions involved in icosahedral contacts suffer a larger increase in constraints than the rest. We found eight sequence sites that would be the most important icosahedral sequence determinants. We discuss our results and compare them with previous work. These findings should contribute to refinement of the current structural data, to the design of assays that explore the role of these positions, to the structural characterization of new sequences, and to initiation of a study of the underlying evolutionary mechanisms.

Descripción: The crude polysaccharide from cystocarpic Callophyllis variegata was fractionated with potassium chloride yielding three minor fractions which precipitated between 0.05-0.10 M KCl, 1.20-1.25 M KCl and 1.80-2.00 M KCl, and a main product soluble in 2.00 M KCl. These fractions were analysed and structural analysis of the major one was carried out by methylation, FT-IR and 13C NMR.

Descripción: The Central Precordillera of San Juan is a thin-skinned fold and thrust belt bounded to the east by the thick-skinned structures of the Eastern Precordillera. The objective of this study is to describe and interpret the structural features found at the southern end of this fold and thrust belt. The lomas de Andapaico's folds are of asymmetric, open chevron type, and are genetically related to fault propagation. Toward the north, the folding becomes tighter and broken by faults. The regional structure consists of an imbricated fan of an array of separated to overlapping fault propagation folds, and out-of-sequence structures related to the Eastern Precordillera uplift. The major décollement thrust is located near the top of the San Juan Formation limestone. Deformation occurred in two main stages. First, an imbricate array of fault-propagation folds was developed as the thrust front migrated toward the foreland. Then, the uplift of the eastern Precordillera impeded the migration of the thrust front and may have caused the development of out-of-sequence structures in the Central Precordillera. The minimum horizontal shortening calculated is 4.8 km, and the whole structure shows a southward decreasing shortening that is shown by structures of different orders and a variety of styles of deformation.

Descripción: Triassic clastic and volcanic rocks from the Precordillera were deposited in the Cuyana rift basin filling half-graben systems. Contractional/transpressional Andean tectonics leads to the almost complete inversion of some portions of the basin which resulted in present-day isolated, structurally controlled outcrops of these Triassic rocks. In the Southern Precordillera both the degree of Neogene tectonic inversion and structural compexities are variable. At the regional scale, these variations in Andean deformation are related to first order anisotropies like the Cuyana basin borders and previous shear zones of Permian age (San Rafael orogenic phase). This paper focuses on the kinematic analysis done in the Cerro Manantial thrust sheet area (Cordón San Bartolo, central sector of the South Precordillera) where tectonic inversion was not that strong and the influence of oblique strain zones is practically null. Four sets of extensional/ transtensional faults were recognized affecting Triassic sedimentary rocks of the El Cielo Formation (Uspallata Group) at the Quebrada El Salto. Fault displacements are of decimetric to metric scale. Mesoscopic kinematic indicators (en-échèlon tensional gashes, Riedel shear fractures, sigmoidal fractures) were measured. Once Andean deformation was restored, a NNE direction for the Triassic extension was determined. Considering a northern branch of the Cuyana basin trending NNW (Az. 150°) and oblique to the direction of extension (Az. 35-40°), a sinistral strike-slip component could be inferred for this portion of the basin.

Descripción: The Atuel depocentre corresponds to a Late Triassic - Early Jurassic NNW-trending subbasin, located in the northern sector of the Neuquén basin. Based on pre-existing stratigraphical data and present structural analysis we propose that the Atuel depocentre is bounded by the presence of two NNW-trending major normal faults, named Alumbre and La Manga. These faults are inferred to have controlled the development of two west-facing half-grabens: the Río Blanco, a completely emerged half-graben, and the western Arroyo Malo, a completely submerged half-graben. The structural model presented here is based on the assumption that both, the basement structural grain and the regional extension direction, exerted a first-order control in the development and evolution of the Atuel depocentre. During the early stage of rifting (pre-Rhaetian - Middle Hettangian) the pre-Triassic Alumbre and La Manga faults reactivated in an oblique mode. During the second episode of rifting, both Alumbre and La Manga faults continued to play, while WNW-trending normal fault developed in order to accommodate the strain inside both half-grabens. The third extensional event began with an abrupt marine rise inside the Arroyo Malo half-graben during late Middle Hettangian, as a result of the last displacement of the Alumbre fault, and finished with an abrupt marine drop associated with the desactivation of the La Manga fault.

Descripción: Located at the transitional southern end (33o S) of the Pampean flat-slab, the Tertiary volcanic belt records the eastward migration of the Andean volcanic arc due to the flattening of the Nazca Plate in Mio-Pliocene times. The tertiary volcanic belt encompasses several very important metallogenetic districts in the San Luis Pampean Ranges. Volcanic rocks and associated ore-deposits crop out following a NW-WNW trending belt at La Carolina, Cañada Honda - Cerros Largos, Cerros del Rosario and El Morro volcanic fields. The available geochronological data indicate that the volcanic activity began early at the western end of the belt and ended ~ 10 Ma later at its eastern border. Cañada Honda district represents the oldest and longest-lived volcanic field of the tertiary volcanic belt. It records eruptive events and related hydrothermal alteration from 12-13 Ma to 7.3 Ma, including lavas and volcaniclastic products. Preliminary structural analysis shows that previous structures have strongly controlled, either directly or indirectly, the emplacement of volcanic rocks and related mineral deposits. Kinematic and strain fabric analyses allow to recognize two volcano-tectonic associations. One of these associations would be related to dextral reactivations of structures parallel to basement foliation. On the other hand, the main one would be linked with the generation of two volcano-tectonic depressions which are aligned in a NW-WNW direction. Their dominant structures trend NW-WNW and reveal sinistral-normal motions, both at local and Tertiary volcanic belt scales.

Descripción: The Antarctic icefish Chaenocephalus aceratus lacks the globins common to most vertebrates, hemoglobin and myoglobin, but has retained neuroglobin in the brain. This conserved globin has been cloned, over-expressed and purified. To highlight similarities and differences, the structural features of the neuroglobin of this colourless-blooded fish were compared with those of the well characterised human neuroglobin as well as with the neuroglobin from the retina of the red blooded, hemoglobin and myoglobin-containing, closely related Antarctic notothenioid Dissostichus mawsoni. A detailed structural and functional analysis of the two Antarctic fish neuroglobins was carried out by UV-visible and Resonance Raman spectroscopies, molecular dynamics simulations and laser-flash photolysis. Similar to the human protein, Antarctic fish neuroglobins can reversibly bind oxygen and CO in the Fe 2+ form, and show six-coordination by distal His in the absence of exogenous ligands. A very large and structured internal cavity, with discrete docking sites, was identified in the modelled three-dimensional structures of the Antarctic neuroglobins. Estimate of the free-energy barriers from laser-flash photolysis and Implicit Ligand Sampling showed that the cavities are accessible from the solvent in both proteins. Comparison of structural and functional properties suggests that the two Antarctic fish neuroglobins most likely preserved and possibly improved the function recently proposed for human neuroglobin in ligand multichemistry. Despite subtle differences, the adaptation of Antarctic fish neuroglobins does not seem to parallel the dramatic adaptation of the oxygen carrying globins, hemoglobin and myoglobin, in the same organisms. © 2012 Giordano et al.

Descripción: A rock-avalanche (named Las Cañas) was distinguished near the Potrero de Leyes rock-avalanche previously recognized in the southern Sierras Pampeanas. It is located on the western slope of the Sierra Grande de San Luis (San Luis Province), which is regarded as the range uplift front during the Andean tectonism. On account of its greater degradation than the Potrero de Leyes rock-avalanche, the deposits described here are considered to be older in age. Their morphometric attributes could be only roughly calculated, because fluvial erosion has removed a large portion of its initial shape and volume. The avalanche-related deposits form round-shaped hills, which can be distinguished from alluvial fan deposits by their higher altitude, photogeological signature and degree of degradation. Two fault sets have also modified its original surface configuration. It is considered that this phenomenon was also triggered by an earthquake. Hence, the recognition and analysis of these geomorphological processes provides a useful addition to palaeosismological analysis and is significant for an adequate evaluation of the the seismic hazard of this region. © 1998 Asociación Geológica Argentina.

Descripción: In the present work, we have used the papillomavirus E7 oncoprotein to pursue structure-function and evolutionary studies that take into account intrinsic disorder and the conformational diversity of globular domains. The intrinsically disordered (E7N) and globular (E7C) domains of E7 show similar degrees of conservation and co-evolution. We found that E7N can be described in terms of conserved and coevolving linear motifs separated by variable linkers, while sequence evolution of E7C is compatible with the known homodimeric structure yet suggests other activities for the domain. Within E7N, inter-residue relationships such as residue co-evolution and restricted intermotif distances map functional coupling and co-occurrence of linear motifs that evolve in a coordinate manner. Within E7C, additional cysteine residues proximal to the zinc-binding site may allow redox regulation of E7 function. Moreover, we describe a conserved binding site for disordered domains on the surface of E7C and suggest a putative target linear motif. Both homodimerization and peptide binding activities of E7C are also present in the distantly related host PHD domains, showing that these two proteins share not only structural homology but also functional similarities, and strengthening the view that they evolved from a common ancestor. Finally, we integrate the multiple activities and conformations of E7 into a hierarchy of structure-function relationships. © 2012 Chemes et al.

Descripción: Aims: To study the modification of the cell wall of Lactobacillus casei ATCC 393 grown in high salt conditions. Methods and Results: Differences in the overall structure of cell wall between growth in high salt (MRS + 1 mol l -1 NaCl; N condition) and control (MRS; C condition) conditions were determined by transmission electronic microscopy and analytical procedures. Lactobacillus casei cells grown in N condition were significantly larger than cells grown under unstressed C condition. Increased sensitivity to mutanolysin and antibiotics with target in the cell wall was observed in N condition. Purified cell wall also showed the increased sensitivity to lysis by mutanolysin. Analysis of peptidoglycan (PG) from stressed cells showed that modification was at the structural level in accordance with a decreased PG cross-link involving penicillin-binding proteins (PBP). Nine PBP were first described in this species and these proteins were expressed in low percentages or presented a modified pattern of saturation with penicillin G (Pen G) during growth in high salt. Three of the essential PBP were fully saturated in N condition at lower Pen G concentrations than in C condition, suggesting differences in functionality in vivo. Conclusions: The results show that growth in high salt modified the structural properties of the cell wall. Significance and Impact of Study: Advances in understanding the adaptation to high osmolarity, in particular those involving sensitivity to lysis of lactic acid bacteria.

Descripción: In silico analyses have revealed a conserved protein domain (CHDL) widely present in bacteria that has significant structural similarity to eukaryotic cadherins. A CHDL domain was shown to be present in RapA, a protein that is involved in autoaggregation of Rhizobium cells, biofilm formation, and adhesion to plant roots as shown by us and others. Structural similarity to cadherins suggested calcium-dependent oligomerization of CHDL domains as a mechanistic basis for RapA action. Here we show by circular dichroism spectroscopy, light scattering, isothermal titration calorimetry, and other methods that RapA2 from Rhizobium leguminosarum indeed exhibits a cadherin-like β-sheet conformation and that its proper folding and stability are dependent on the binding of one calcium ion per protein molecule. By further in silico analysis we also reveal that RapA2 consists of two CHDL domains and expand the range of CHDLcontaining proteins in bacteria and archaea. However, light scattering assays at various concentrations of added calcium revealed that RapA2 formed neither homo-oligomers nor hetero-oligomers with RapB (a distinct CHDL protein), indicating that RapA2 does not mediate cellular interactions through a cadherin-like mechanism. Instead, we demonstrate that RapA2 interacts specifically with the acidic exopolysaccharides (EPSs) produced by R. leguminosarum in a calcium-dependent manner, sustaining a role of these proteins in the development of the biofilm matrix made of EPS. Because EPS binding by RapA2 can only be attributed to its two CHDL domains, we propose that RapA2 is a calcium-dependent lectin and thatCHDLdomains in various bacterial and archaeal proteins confer carbohydrate binding activity to these proteins. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.

Descripción: The major cAMP receptors in eukaryotes are the regulatory (R) subunits of PKA, an allosteric enzyme conserved in fungi through mammals. While mammals have four R-subunit genes, Saccharomyces cerevisiae has only one, Bcy1. To achieve a molecular understanding of PKA activation in yeast and to explore the evolution of cyclic-nucleotide binding (CNB) domains, we solved the structure of cAMP-bound Bcy1(168-416). Surprisingly, the relative orientation of the two CNB domains in Bcy1 is very different from mammalian R-subunits. This quaternary structure is defined primarily by a fungi-specific sequence in the hinge between the αB/αC helices of the CNB-A domain. The unique interface between the two CNB domains in Bcy1 defines the allosteric mechanism for cooperative activation of PKA by cAMP. Some interface motifs are isoform-specific while others, although conserved, play surprisingly different roles in each R-subunit. Phylogenetic analysis shows that structural differences in Bcy1 are shared by fungi of the subphylum Saccharomycotina. © 2010 Elsevier Ltd.

Descripción: In the same way that cry genes, coding for larvicidal delta endotoxins, constitute a large and diverse gene family, the cyt genes for hemolytic toxins seem to compose another set of highly related genes in Bacillus thuringiensis. Although the occurrence of Cyt hemolytic factors in B. thuringiensis has been typically associated with mosquitocidal strains, we have recently shown that cyt genes are also present in strains with different pathotypes; this is the case for the morrisoni subspecies, which includes strains biologically active against dipteran, lepidopteran, and coleopteran larvae. In addition, while one Cyt type of protein has been described in all of the mosquitocidal strains studied so far, the present study confirms that at least two Cyt toxins coexist in the more toxic antidipteran strains, such as B. thuringiensis subsp. israelensis and subsp. morrisoni PG14, and that this could also be the case for many others. In fact, PCR screening and Western blot analysis of 50 B. thuringiensis strains revealed that cyt2-related genes are present in all strains with known antidipteran activity, as well as in some others with different or unknown host ranges. Partial DNA sequences for several of these genes were determined, and protein sequence alignments revealed a high degree of conservation of the structural domains. These findings point to an important biological role for Cyt toxins in the final in vivo toxic activity of many B. thuringiensis strains.

Descripción: Continuity and evolution in time of the horizontal stress direction in the Neuquen Basin area, derived from the analysis of recent borehole data and orientation of volcanic dykes measured in outcrop in the Cara Cura and Reyes Ranges is presented. The bitumen dykes along the Neuquén Basin were formed during Paleocene - Eocene in a context where the maximum stress was horizontal and had a NE. Within the analyzed volcanic dykes two major groups have been recognized, group i (NE orientation) and group ii (NNE orientation) and a secondary group iii (NW orientation). The age of these dykes is still not well established, but they were related to a Late Oligocene - Miocene magmatic event. Both for the volcanic and bitumen dykes a type i group (ENE-NE orientation) has been recognized, evidencing the maximum stress direction at the time they were formed. Beyond the uncertainties in the volcanic and bitumen dykes age, it is interpreted that during great part of Tertiary, the orientation of the horizontal maximum stress was NE. However, the breakout data shows that the actual horizontal maximum stress is a little different with a ENE mean direction. This change in the direction of stress is consistent with the change in the subduction vector produced between the Eocene and today.

Descripción: We assessed the intracellular association states of the Parkinson's disease related protein α-synuclein (AS) in living cells by transfection with a functional recombinant mutant protein (AS-C4) bearing a tetracysteine tag binding the fluorogenic biarsenical ligands FlAsH and ReAsH, The aggregation states of AS-C4 were assessed by in situ microscopy of molecular translational mobility with FRAP (fluorescence recovery after photobleaching) and of local molecular density with confocal fluorescence anisotropy (CFA). FRAP recovery was quantitative and rapid in regions of free protein, whereas AS in larger aggregates was>80% immobile. A small 16% recovery characterized by an apparent diffusion constant of 0.03-0.04 μm 2/s was attributed to the dynamics of smaller, associated forms of AS-C4 and the exchange of mobile species with the larger immobile aggregates. By CFA, the larger aggregates exhibited high brightness and very low anisotropy, consistent with homoFRET between closely packed AS, for which a Förster distance (R o) of 5.3 nm was calculated. Other bright regions had high anisotropy values, close to that of monomeric AS, and indicative of membrane-associated protein with both low mobility and low degree of association. The anisotropy-fluorescence intensity correlations also revealed regions of free protein or of small aggregates, undetectable by conventional fluorescence imaging alone. The combined strategy (FRAP+CFA) provides a highly sensitive means for elucidating both the dynamics and structural features of protein aggregates and other intracellular complexes in living cells, and can be extended to other amyloid systems and to drug screening protocols. © 2011 Roberti et al.

Descripción: To characterize the mechanism of chloroplast fructose‐1,6‐bisphosphatase activation, we have examined kinetic and structural changes elicited by protein perturbants and reductants. At variance with its well‐known capacity for enzyme inactivation, 150 mM sodium trichloroacetate yielded an activatable chloroplast fructose‐1,6‐bisphosphatase in the presence of 1.0 mM fructose 1,6‐bisphosphate and 0.1 mM Ca2+. Other sugar bisphosphates did not replace fructose 1,6‐bisphosphate whereas Mg2+ and Mn2+ were functional in place of Ca2+. Variations of the emission fluorescence of intrinsic fluorophores and a noncovalently bound extrinsic probe [2‐(P‐toluidinyl)naphthalene‐6‐sulfonate] indicated the presence of conformations different from the native form. A similar conclusion was drawn from the analysis of absorption spectra by means of fourth‐derivative spectrophotometry. The effect of these conformational changes on the reductive process was studied by subsequently incubating the enzyme with dithiothreitol. The reaction of chloroplast fructose‐1,6‐bisphosphatase with dithiothreitol was accelerated 13‐fold by the chaotropic anion: second‐order rate constants were 48.1 M−1· min−1 and 3.7 M−1· min−1 in the presence and in the absence of trichloroacetate, respectively. Thus, the enhancement of the reductive activation by compounds devoid of redox activity illustrated that the modification of intramolecular noncovalent interactions of chloroplast fructose‐1,6‐bisphosphatase plays an essential role in the conversion of enzyme disulfide bonds to sulfhydryl groups. In consequence, a conformational change would operate concertedly with the reduction of disulfide bridges in the light‐dependent activation mediated by the ferredoxin–thioredoxin system. Copyright © 1994, Wiley Blackwell. All rights reserved