Parallel Folding Research Articles

Observation of multistate kinetics during the slow folding and unfolding of barstar.

The kinetics of the slow folding and unfolding reactions of barstar, a bacterial ribonuclease inhibitor protein, have been studied at 23(+/-1) degrees C, pH 8, by the use of tryptophan fluorescence, far-UV circular dichroism (CD), near-UV CD, and transient mixing (1)H nuclear magnetic resonance (NMR) spectroscopic measurements in the 0-4 M range of guanidine hydrochloride (GdnHCl) concentration. The denaturant dependences of the rates of folding and unfolding processes, and of the initial and final values of optical signals associated with these kinetic processes, have been determined for each of the four probes of measurement. Values determined for rates as well as amplitudes are shown to be very much probe dependent. Significant differences in the intensities and rates of appearance and disappearance of several resolved resonances in the real-time one-dimensional NMR spectra have been noted. The NMR spectra also show increasing dispersion of chemical shifts during the slow phase of refolding. The denaturant dependences of rates display characteristic folding chevrons with distinct rollovers under strongly native as well as strongly unfolding conditions. Analyses of the data and comparison of the results obtained with different probes of measurement appear to indicate the accumulation of a myriad of intermediates on parallel folding and unfolding pathways, and suggest the existence of an ensemble of transition states. The energetic stabilities of the intermediates estimated from kinetic data suggest that they are approximately half as stable as the fully folded protein. The slowness of the folding and unfolding processes (tau = 10-333 s) and values of 20.5 (+/-1.4) and 18 (+/-0.5) kcal mol(-)(1) for the activation energies of the slow refolding and unfolding reactions suggest that proline isomerization is involved in these reactions, and that the intermediates accumulate and are therefore detectable because the slow proline isomerization reaction serves as a kinetic trap during folding.

Effects of proline mutations on the folding of staphylococcal nuclease.

Effects of proline isomerizations on the equilibrium unfolding and kinetic refolding of staphylococcal nuclease were studied by circular dichroism in the peptide region (225 nm) and fluorescence spectra of a tryptophan residue. For this purpose, four single mutants (P11A, P31A, P42A, and P56A) and four multiple mutants (P11A/P47T/P117G, P11A/P31A/P47T/P117G, P11A/P31A/P42A/P47T/P117G, and P11A/P31A/P42A/P47T/P56A/P117G) were constructed. These mutants, together with the single and double mutants for Pro47 and Pro117 constructed in our previous study, cover all six proline sites of the nuclease. The P11A, P31A, and P42A mutations did not change the stability of the protein remarkably, while the P56A mutation increased protein stability to a small extent by 0.5 kcal/mol. The refolding kinetics of the protein were, however, affected remarkably by three of the mutations, namely, P11A, P31A, and P56A. Most notably, the amplitude of the slow phase of the triphasic refolding kinetics of the nuclease observed by stopped-flow circular dichroism decreased by increasing the number of the proline mutations; the slow phase disappeared completely in the proline-free mutant (P11A/P31A/P42A/P47T/P56A/P117G). The kinetic refolding reactions of the wild-type protein assessed in the presence of Escherichia coli cyclophilin A showed that the slow phase was accelerated by cyclophilin, indicating that the slow phase was rate-limited by cis-trans isomerization of the proline residues. Although the fast and middle phases of the refolding kinetics were not affected by cyclophilin, the amplitude of the middle phase decreased when the number of the proline mutations increased; the percent amplitudes for the wild-type protein and the proline-free mutants were 43 and 13%, respectively. In addition to these three phases detected with stopped-flow circular dichroism, a very fast phase of refolding was observed with stopped-flow fluorescence, which had a shorter dead time (3.6 ms) than the stopped-flow circular dichroism. The following conclusions were drawn. (1) The effects of the P11A, P31A, and P56A mutations on the refolding kinetics indicate that the isomerizations of the three proline residues are rate-limiting, suggesting that the structures around these residues (Pro11, Pro31, and Pro56) may be organized at an early stage of refolding. (2) The fast phase corresponds to the refolding of the native proline isomer, and the middle phase whose amplitude has decreased when the number of proline mutations was increased may correspond to the slow refolding of non-native proline isomers. The occurrence of the fast- and slow-refolding reactions together with the slow phase rate-limited by the proline isomerization suggests that there are parallel folding pathways for the native and non-native proline isomers. (3) The middle phase did not completely disappear in the proline-free mutant. This suggests that the slow-folding isomer is produced not only by the proline isomerizations but also by another conformational event that is not related to the prolines. (4) The very fast phase detected with the fluorescent measurements suggests that there is an intermediate at a very early stage of kinetic refolding.

Stability and folding of the cell cycle regulatory protein, p13suc1

p13suc1 (suc1) is a member of the CDC28 kinase specific family of cell cycle regulatory proteins that bind to the cyclin-dependent kinase CDK2 and regulate its activity. suc1 has two distinct conformational and assembly states, a compact globular monomer and a β strand-exchanged dimer. The dimerisation is an example of domain-swapping, and is mediated by a molecular hinge mechanism that is conserved across the entire CKS family. It has been proposed that the function of suc1 may be modulated by the dimerisation process with monomer-dimer switching occurring in response to a change in the cell environment. We have investigated the stability and folding of suc1 as a first step in determining the mechanism and functional role of the strand exchange. Suc1 unfolds reversibly at equilibrium in a two-state manner with a free energy of unfolding of 7.2 kcal mol−1. The kinetics of folding and unfolding are complex, and double-jump stopped-flow methods revealed that there are at least three parallel folding pathways arising from distinct unfolded and partly folded, intermediate states. The major population of unfolded species fold rapidly according to a three-state mechanism, D1 - >I1 - >N, with a rate constant for the formation of native species, N, from the intermediate, I1, of 65 s−1 in water. Two minor populations of unfolded molecules fold more slowly. Folding of one population is limited by proline isomerisation in a partly folded state, and some expansion of the protein is required for isomerisation to occur. The other population could be assigned to rate-limiting isomerisation of the peptidyl-proline bond of residue 90, which is located in the molecular hinge. A minor, fast phase was detected in the unfolding kinetics that corresponds to unfolding of a small population of a distinct native-like form. Heterogeneity was removed upon mutation of Pro90 to Ala. The unfolding kinetics of the strand-exchanged dimer were also investigated and showed that the dimer unfolds at the same rate as the monomer.

Analogue modeling of faulting pattern, ductile deformation, and vertical motion in strike‐slip fault zones

The relationship between faulting, ductile deformation, and vertical displacement in provinces of strike‐slip faults were analyzed using analogue modeling. The described experiment considered a two‐layer, small‐scale model for the lithosphere, set on a low‐viscosity fluid that allowed free isostatic compensation. The development of the faults and their orientation follow generally Riedel's model, but fault spacing depends on the thickness of the brittle layer, and lateral displacement of the brittle layer was associated with series of deep, elongated depressions that developed along the trace of the principal strike‐slip fault. The depressions correspond to local thinning of the brittle layer, and the amount of thinning is more than 60% in places. The underlying ductile layer displayed two types of superimposed deformation, namely a series of tight, parallel folds, occurring on top of elongated domes. The folds are attributed to the compressive component of the strike‐slip displacement, and the updoming to the extensional component. The elongated domes are located beneath the superficial depressions, and the deeper troughs underlie shallow uplifted structures in the deformed band. Significant vertical motion was observed along faults that are considered as perfectly strike‐slip faults, according to the classical Riedel model. The thinning of the brittle layer, and the deep deformation of the ductile layer, are in good agreement with actual examples of pull‐apart basins and elongated swells in large strike‐slip zones. A new structural pattern developed during strike‐slip shear is proposed, relating the geometrical relationships between faults, folds, and elongated domes to the stress axes.

A scanning electron microscopy study of peritoneal stomata in different peritoneal regions

Peritoneal stomata constitute the principal pathways for the drainage of intraperitoneal contents from the peritoneal cavity to the lymphatic system and have been claimed to be exclusively restricted to the peritoneal surface of the diaphragm. This concept has been revised by the demonstration of peritoneal stomata in the omental, mesenteric, ovaric and pelvic peritoneum. Therefore, the aim of this study was to further assess peritoneal surfaces of several other abdominal organs and of the abdominal wall with special reference to the occurrence of peritoneal stomata. The peritoneum covering the spleen, stomach, intestine, liver, diaphragm and anterior abdominal wall obtained from rats was examined by scanning electron microscopy. Whereas the splenic and hepatic peritoneal surfaces were composed of uniformly distributed cuboidal mesothelial cells, the gastric and intestinal peritoneal surfaces were arranged in parallel folds composed of prominent mesothelial cells with elongated finger-like cytoplasmic processes. In addition to diaphragmatic peritoneal stomata, mesothelial openings were also found on the peritoneal surfaces covering the anterior abdominal wall and the liver. The parietal peritoneal stomata were arranged in clusters, oval in shape and delimited by flattened mesothelial cells exposing the underlying submesothelial connective tissue. The hepatic mesothelial openings formed by deep channel-like gaps of adjacent cuboidal mesothelial cells were almost completely occluded by a dense microvillous coat. As the submesothelial connective tissue was not identifiable with certainty, the mesothelial openings were regarded as corresponding to stoma-like structures. These findings yield further evidence that peritoneal stomata are obviously not confined to the diaphragmatic area but extend to other peritoneal regions. It is therefore suggested that these extra-diaphragmatic parietal and visceral peritoneal surfaces contribute to the absorption capacity of the entire peritoneum and are subsequently involved in either therapeutic procedures or pathological processes affecting the peritoneal cavity.

Formation of multiple fold generations on lava flow surfaces: Influence of strain rate, cooling rate, and lava composition

If the surface crust of an advancing lava flow experiences compression, it may deform into a series of parallel folds, whose long axes are perpendicular to the flow direction. Under continued compression, a second generation of larger folds may appear, superimposed on the first. The ratio, Λ, of the second-generation fold wavelength ( L 2) to the first-generation fold wavelength ( L 1) reflects the relative importance of shortening versus cooling at the flow surface in thickening the crust. On Earth, the dominance of one or the other of these two mechanisms can be empirically correlated with composition. The characteristic values of Λ are 5.1±1.1 for basalts, 2.5±0.7 for andesites, 2.1±0.3 for dacites, and 1.8±0.4 for rhyolites. Although there is overlap among the more evolved lava compositions, basalts have consistently and significantly different Λ values, because shortening thickens the surface crust of basalt flows more rapidly than does cooling, whereas the converse is true for more evolved lavas. With appropriate scaling, these results can be applied to extraterrestrial folded flows to constrain lava compositions. Results obtained by applying this model to folded Martian and Venusian lavas suggest that they have compositions more evolved than basalt.

The geometry of unfolding tree leaves

Leaves of hornbeam (Carpinus betulus) and beech (Fagus sylvaticus) were modelled to a first approximation as plane surfaces, with straight parallel folds, using numerical methods. In both species t...

Quantified vertical motions and tectonic evolution of the SE Pyrenean foreland basin

Abstract Local isostatic backstripping analysis is performed across the eastern part of the Ebro foreland basin between the Pyrenees and the Catalan Coastal Ranges. The subsidence analysis is based on two well-dated field-based sections and four oil-wells aligned parallel to the tectonic transport direction of the eastern Pyrenean orogen. The marine infill of the foreland basin is separated into four, third-order, transgressive-regressive depositional cycles. The first and second depositional cycles are located in the Ripoll piggy-back basin and the third and fourth ones are located south of the syn-depositional emergent Vall-fogona thrust. Subsidence curves display a typical convex-up shape with inflection points recording the onset of rapid tectonic subsidence. Inflection points coincide roughly with the base of depositional cycles. Rates of tectonic subsidence are less than 0.1 mm a −1 in distal parts of the basin and up to 0.53 mm a −1 in proximal parts during second depositional cycle. Younger depositional cycles show maximum rates of tectonic subsidence of 0.26 mm a −1 . The locus of subsidence within the basin migrated southward at a rate of c . 10 mm a −1 . This flexural wave crossed the complete Ebro foreland basin in 10–11 Ma. The intraplate Catalan Coastal Ranges at the southeastern margin of the Ebro foreland basin produced an increase of tectonic subsidence rate at 41.5 Ma. Maximum rates of tectonic subsidence coincide with deep-marine infill of the basin, maximum rates of shortening and thrust front advance, and low topographic relief orogenic wedge. Transgressive-regressive depositional cycles can be controlled partly by reductions of available space within the basin during tectonic thickening of the sedimentary pile by layer parallel shortening, folding and thrusting. Although much less constrained, an approximation of post-thrusting exhumation and isostatic and tectonic uplift, as well as a first determination of possible amounts of eroded material of parts of the Ebro basin illustrate the impact of post-depositional erosion and uplift on the foreland.

Creating a Modern "Zone of Genocide": The Impact of Nation- and State-Formation on Eastern Anatolia, 1878-1923

The persistence of or near-genocidal incidents from 1890s through 1990s, committed by Ottoman and successor Turkish and Iraqi states against Armenian, Kurdish, Assyrian, and Pontic Greek communities in Eastern Anatolia, is striking. This article traces origins of these incidents by examining emerging Armenian, Turkish, and Kurdish national movements and their competition for region's resources. It argues that creation of this zone of genocide in Eastern Anatolia cannot be understood in isolation, but only in light of role played by Great Powers in emergence of a Western-led international system. This article examines patterns of and ethnic hostility in Eastern Anatolia from late nineteenth to early twentieth centuries. This region has been described as a geographic unit of some 120,000 square miles.1 Its core is a largely steppe-like mountain plateau, with Lake Van and Mount Ararat its most significant physical features. To north it is bounded by Black Sea after a dramatic descent via Pontus range; Caucasus mountains provide a natural barrier in northeast. To south, it falls away in a series of steep, parallel folds descending along headwaters of Tigris and Euphrates, to Jazira, great SyrianMesopotamian plain. Eastern Anatolia consists of six Ottoman administrative vilayets that most concerned European powers in late nineteenth century due to the Armenian Question, as well as vilayet of Trabzon and a substantial part of Mosul. This would embrace historic western Armenia, with exception of Cilicia, but not eastern Armenia (and thus modern independent republic of that name). It would also include northern and central core of Kurdistan, some of which today lies in northern Iraq. Eastern Anatolia is our focus because it is at once an arena in which competing national interests have laid claim to its territory and assets, and a geographic region that since 1890s has been repeatedly plagued by genocidal killings. Within

Kinetics of peptide folding: computer simulations of SYPFDV and peptide variants in water

The folding of Ser-Tyr-Pro-Phe-Asp-Val (SYPFDV), and sequence variants of this peptide (SYPYD and SYPFD) are studied computationally in an explicit water environment. An atomically detailed model of the peptide is embedded in a sphere of TIP3P water molecules and its optimal structure is computed by simulated annealing. At distances from the peptide that are beyond a few solvation shells, a continuum solvent model is employed. The simulations are performed using a mean field approach that enhances the efficiency of sampling peptide conformations. The computations predict a small number of conformations as plausible folded structures. All have a type VI turn conformation for the peptide backbone, similar to that found using NMR. However, some of the structures differ from the experimentally proposed ones in the packing of the proline ring with the aromatic residues. The second most populated structure has, in addition to a correctly folded backbone, the same hydrophobic packing as the conformation measured by NMR.Our simulations suggest a kinetic mechanism that consists of three separate stages. The time-scales associated with these stages are distinct and depend differently on temperature. Electrostatic interactions play an initial role in guiding the peptide chain to a roughly correct structure as measured by the end-to-end distance. At the same time or later the backbone torsions rearrange due to local tendency of the proline ring to form a turn: this step depends on solvation forces and is helped by loose hydrophobic interactions. In the final step, hydrophobic residues pack against each other.We also show the existence of an off the pathway intermediate, suggesting that even in the folding of a small peptide “misfolded” structures can form. The simulations clearly show that parallel folding paths are involved.Our findings suggest that the process of peptide folding shares many of the features expected for the significantly larger protein molecules.

Plaques très comprimées

We discuss the ‘post-buckling’ of a thin elastic plate. The application of the von Kármán theory allows us to find the threshold of buckling, as a function of the various physical parameters. We examine the solution well above threshold. We propose that in this limit, the solution is a series of parallel straight folds that merge with the lateral boundaries through a cascade of folds of decreasing length scale.

Folding of the disulfide-bonded β-sheet protein tendamistat: rapid two-state folding without hydrophobic collapse

We investigated the reversible folding and unfolding reactions of the small 74 amino acid residue protein tendamistat. The secondary structure of tendamistat contains only β-sheets and loop regions and the protein contains two disulfide bonds. Fluorescence-detected refolding kinetics of tendamistat (disulfide bonds intact) comprise of a major rapid fast reaction (τ=10 ms in water) and two minor slow reactions. In the fast reaction 80% of the unfolded molecules are converted to native protein. The two slow reactions are part of a parallel slow folding pathway. On this pathway the rate-limiting step in the formation of native molecules is cis to trans isomerization of at least one of the three trans Xaa-Pro peptide bonds. This reaction is catalyzed efficiently by the enzyme peptidyl-prolyl cis-trans isomerase. Comparison of kinetic data with equilibrium unfolding transitions shows that the fast folding pathway follows a two-state process without populated intermediate states. Additionally, various sensitive tests did not detect any rapid chain collapse during tendamistat folding prior to the acquisition of the native three-dimensional structure. These results show that pre-formed disulfide bonds do not prevent efficient and rapid protein folding.

A kinematic model for the formation of duplex systems with a perfectly planar roof thrust

We present a cross-sectional kinematic forward model for the formation of duplexes with a perfectly planar roof thrust. The major assumptions are a constant dip and constant spacing of the ramps in the undeformed state and sequential deformation in the direction of tectonic transport, with equal displacement along each ramp. The model is based on a coordinate transformation that simulates flexural slip parallel to the active fault surface. This causes angular parallel folds and keeps the layer thickness constant, except in the forelimbs of the horses. Attempts by previous workers to simulate the formation of duplexes with a perfectly planar roof thrust, on the other hand, were based on the assumptions of constant bed thickness and bed length, or a different topology of the axial planes delimiting the forelimbs of the horses, and resulted in corrugated roof thrusts. We show that it is not possible to form a flat roof duplex type and preserve the forelimb thickness of the horses under flexural slip parallel to the active fault. We describe duplexes by three parameters which are the separation s between ramps, the ramp length l, and the displacement u along the ramps. In a u s vs l s diagram, duplexes with a perfectly planar roof thrust, resulting from numerical experiments with our kinematic algorithm, occupy specific families of straight lines. Our results are independent of the dip or internal geometry of the thrust ramps.

Specular microscopy of the corneal endothelial cells in common marmosets.

The corneal endothelia of 12 female common marmosets (age: 12-18 months) were examined with a contact-type specular microscope under general anesthesia. The specular microscopy showed uniform-sized, hexagonal endothelia arranged regularly on the innermost layer of the cornea. The endothelial plane was smooth; however, it occasionally had irregular undulation or parallel folds. The cell density (cells/mm2) in common marmosets was similar to that in cynomolgus monkeys.

Flexural flow folding: Does it occur in nature?

Research Article| March 01, 1996 Flexural flow folding: Does it occur in nature? Peter J. Hudleston; Peter J. Hudleston 1Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455 Search for other works by this author on: GSW Google Scholar Susan H. Treagus; Susan H. Treagus 2Department of Geology, University of Manchester, Manchester, M13 9PL, United Kingdom Search for other works by this author on: GSW Google Scholar Labao Lan Labao Lan 1Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455 Search for other works by this author on: GSW Google Scholar Author and Article Information Peter J. Hudleston 1Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455 Susan H. Treagus 2Department of Geology, University of Manchester, Manchester, M13 9PL, United Kingdom Labao Lan 1Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1996) 24 (3): 203–206. https://doi.org/10.1130/0091-7613(1996)024<0203:FFFDIO>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Peter J. Hudleston, Susan H. Treagus, Labao Lan; Flexural flow folding: Does it occur in nature?. Geology 1996;; 24 (3): 203–206. doi: https://doi.org/10.1130/0091-7613(1996)024<0203:FFFDIO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Flexural flow produces a continuous deformation equivalent to that of a flexed deck of cards of vanishing card thickness. It is assumed to be a common process by which parallel folds are formed in nature in competent, anisotropic rock layers. The strain pattern produced by flexural flow contrasts strongly with that produced in parallel folds formed by the bending or buckling of isotropic competent layers, but it has not been documented in nature. Two basic questions are thus: (1) If anisotropy is sufficiently large, will flexural flow develop, and (2) if so, are competent rocks sufficiently anisotropic for them to respond to deformation by flexural flow? A measure of planar anisotropy, A, is given by the ratio of viscosity in shortening to viscosity in shear. Finite-element modeling indicates that if the value of this ratio is greater than about 50, the strain pattern in a buckle fold in a competent layer will be almost indistinguishable from one of flexural flow. Such a high anisotropy, however, is unlikely in natural competent layers. The most texturally anisotropic rocks tend to be those rich in phyllosilicates, and these usually behave in an incompetent fashion. Common competent rocks, such as those rich in quartz and feldspar, are rarely significantly anisotropic. A strong preferred crystallographic orientation as a result of crystal-plastic flow can produce anisotropic layer behavior, but A is unlikely to exceed ∼10, which is insufficiently great for folding by flexural flow. We thus conclude that flexural flow is unlikely in single competent layers. The aggregate response to deformation, however, of composite layers of alternating competent and incompetent rocks may be highly anisotropic and on average correspond to flexural flow. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

New approach to the study of transient protein conformations: the formation of a semiburied salt link in the folding pathway of barnase.

We use in this study a novel kinetic approach to determine the H+ titration properties of a semiburied salt link in the transition state for unfolding of barnase. The approach is based on changes in the pH dependence of the kinetics upon mutation of a target residue. This makes it relatively insensitive to the absolute value of the stability and, thereby, to artifacts caused by structural rearrangements around the site of mutation. The semiburied salt bridge studied here is between Asp93 and Arg69. Mutation of either residue significantly destabilized the protein, and the pKa value of Asp93 is severely lowered in the native state to below 1 because of the ionic interaction with Arg69. The Asp93-Arg69 salt link appears to be formed early in the folding process; the pKa value of Asp93 in the transition state (approximately 1) is similar to that in the native state, and deletion of the ionic interaction with Arg69 substantially destabilizes the folding intermediate and changes the kinetic behavior from multistate to two-state or close to two-state, depending on the conditions. The results suggest that the formation of ionic interactions within clusters of hydrophobic residues can be important for early folding events and can control kinetically the folding pathway. This is not because of the inherent stability of the salt link but because the presence of two unpaired charges is very unfavorable. The data reveal also that fractional phi values are consistent with a uniformly expanded transition state or one with closely spaced energy levels and not with parallel folding pathways.

The deformation history of an accreted ophiolite sequence: the Internal Liguride units (Northern apennines, Italy)

The Mt. Gottero, Bracco/Val Graveglia and Colli/Tavarone units from the Northern Apennines, Italy, are remnants of the Ligure-Piemontese oceanic lithosphere that were involved in the tectonic events related to convergence between the European and Adria plates. These events included late Paleocene – middle Eocene subduction followed by late Eocene continental collision.These units, referred to as Internal Liguride units, consist of Jurassic ophiolites covered by a thick sedimentary sequence, which includes late Jurassic-Santonian pelagic deposits (chert, Calpionella limestone and Palombini shale) and Campanian-Early Paleocene trench deposits (Val Lavagna shale and Mt. Gottero sandstone) that are overlain by Early Paleocene lower slope deposits (Bocco shale). This sequence is interpreted as recording trenchward motion of the oceanic lithosphere.The structural analysis of the Internal Liguride units reveals a pre-Oligocene deformation history, which includes the following stages:– stage 1: pre-folding, bedding-parallel veins developed during burial and dewatering of a thick sedimentary sequence;– stage 2: D1 phase distinguished by non cylindrical, isoclinal folds with approximately similar geometries. The associated slaty cleavage is characterized by a mineral assemblage related to P/T metamorphic climax of 0.3–0.4 GPa and 180°-300°C. The asymmetric recrystallized tails around detrital minerals and framboidal pyrites indicate a non-coaxial deformation history characterized by top-to-west sense of shear. Cataclastic shear zones developed in the latest stage of D1;– stage 3: D2 phase marked by overturned, parallel folds associated with a crenulation cleavage. The following D3 phase is characterized by gentle folds with a steep axial plane.The sedimentary records and the structural features support the interpretation of the Internal Liguride units as slices of oceanic lithosphere deformed in a subduction setting. Their deformation history probably developed during underthrusting, cohereht underplating and later exhumation in an accretionary wedge related to an east-dipping, low-rate subduction zone.

The Death Valley Turtlebacks Reinterpreted as Miocene-Pliocene Folds of a Major Detachment Surface

Determining the origin of extension parallel folds in metamorphic core complexes is fundamental to understanding the development of detachment faults. An excellent example of such a feature occurs in the Death Valley region of California where a major, undulatory, detachment fault is exposed along the well-known turtleback (antiformal) surfaces of the Black Mountains. In the hanging wall of this detachment fault are deformed strata of the Copper Canyon Formation. New age constraints indicate that the Copper Canyon Formation was deposited from ~6 to 3 Ma. The formation was folded during deposition into a SE-plunging syncline with an axial surface coplanar with that of a synform in the underlying detachment. This relation suggests the turtlebacks are a folded detachment surface formed during large-scale extension in an overall constrictional strain field. The present, more planar, Black Mountains frontal fault system may be the result of out-stepping of a normal fault system away from an older detachment fault that was deactivated by folding.

Free energy landscape for protein folding kinetics: Intermediates, traps, and multiple pathways in theory and lattice model simulations

The implications of thermodynamics of heteropolymers for their folding kinetics are formulated and discussed. The predictions are tested by Monte Carlo simulation of folding of a lattice model 36-monomer proteins at different temperatures. Using a simulated annealing procedure in sequence space, a number of sequences are designed which have sufficiently low energy in a given target conformation. This conformation plays a role of the native structure for the model proteins. The folding transition is found to be cooperative, and the nature of the free energy barrier is studied. At high temperature the barrier is entropic, and at low temperature it is mainly energetic. This can be explained by transformation of the early partly folded intermediate from the disordered state (belonging to the quasicontinuous part of the energy spectrum) at high temperature to the non-native low-energy frozen conformation at low temperature. The latter plays a role of an off-pathway trap. A parallel folding process has been detected at low temperature where direct folding competes with relaxation of the intermediate. The frozen intermediate must unfold to make it possible to form a folding nucleus, which is the prerequisite of subsequent fast descent to the native state.

Application of enhanced satellite-borne images to the relationships between fractures and mineralization in the nam Mae moei-nam Mae Ping area, northern Thailand

The study area is located in the Chiang Mai, Tak, and Mae Hong Son provinces of northern Thailand. Digitally enhanced Landsat TM5 and SPOT images and data on economic minerals deposits were used in the investigation. High-pass filtering and principal component analyses were determined to be the most appropriate enhancement methods. Space-borne image interpretation indicates two major faults: the north-trending Mae Hong Son and the northwest-trending Mae Ping. Both large-scale faults are inferred to be closely related to substantial, nearly parallel folds and thrusts. The four main sets of lineaments observed (north-south, northeast-southwest, northwest-southeast, and east-west) are considered to have an essential role in the occurrences of various mineral deposits. Mineral exploration has emphasized areas where several sets of lineaments cross-cut each other, since the possibility of finding concealed ore bodies or potential target areas is considered quite high. Some sets of lineaments probably control post-Triassic granitoid emplacements both directly and indirectly. Three major granitoid series are recognized in the study area: the Mae Lama (ca. 70 Ma), the Tae Song Yang (ca. 45 Ma), and the Mae Sariang (205–210 Ma) Granites. These peraluminous, S-type granites are closely related to tin, tungsten, and fluorite deposits. Fluorite, barite, manganese, and antimony deposits may be related to the northtrending lineaments. Stibnite deposits may be related to the northeast-trending lineaments. The tin/tungsten deposits are likely related to the east- and northwest-trending lineaments. Ovoid-shaped lineaments, found only at a few locations, are interpreted to indicate the granitoid emplacement and are thought to be important in the generation of concealed mineral deposits. We conclude that the existence of such lineaments is related to the post-Triassic abutment and collision of the Shan-Thai, Indochina, and Western Burma microcontinental blocks.