Equatorial Domain Research Articles

Westward Displacement of Atmospheric East–West Circulation Ameliorated Drought-Induced Conditions in Australia and India during the Major 2023–24 and 1997–98 El Niño Events

Abstract Based on a compilation of widely available climate analysis products, we show evidence for a significant variation in the spatial pattern of the large-scale vertical zonal atmospheric circulation patterns across the equatorial Indo-Australasian domain of the Eastern Hemisphere during the major 2023–24 El Niño event. The region of large-scale subsidence and its associated teleconnection patterns that are usually centered across Indonesia (the “Maritime Continent”) were displaced to the west over the equatorial Indian Ocean. In the record of El Niño events with readily available online dynamical tropospheric fields (one source from 1947 and the other from 1979), this has only been seen two other times, during the strong 1997–98 El Niño and the weaker 1977–78 event. These three events may well be consistent with internal variability, but at present, the reason for such occurrences has not been established.

Diurnal changes in cloud cover in eastern Gabon and their impacts on energy balance, light availability and water demand: a case study of the 2022 dry season

Abstract Western Central Africa is atypical of the equatorial domain as the main dry season is cloudier than the rainy seasons. To understand this cloud cover's diurnal evolution, we set-up an infrared camera and acquired measurements of the total cloud cover fraction (TCF) and cloud optical depth at Bambidie, Gabon (0°44’30.5” S,12°58’12.4” O) from May to October 2022. Diurnal variations in TCF can be summarized into four types, mostly discretized through the timing and duration of clouds clearing in the afternoon (Early afternoon Clearing: EaC, Late afternoon Clearing: LaC and Clear Night: CNi) while one type (No Clearing: NoC) shows overcast conditions all day long. Meteorological measurements show that NoC days record 50W/m2 less shortwave incoming surface radiation resulting in daytime temperatures 1°C lower than the seasonal norm, but 20% more diffuse light and 0.5mm/day less ETo. Conversely, EaC days record 50W/m2 more shortwave incoming surface radiation leading to temperatures 1.5°C higher than the seasonal norm, but 40% more direct light. The larger water demand (0.5mm/day more ETo) is partly compensated by more frequent rainfall at night-time. The SAFNWC satellite estimates well capture the TCF variations for most of the 4 types. They confirm that TCF is dominated by very low and low clouds whose dissipation in the afternoon and evolution into fractional and cumuliform convective clouds explains the clearings on EaC and LaC days. Satellite estimates also show that the 4 types of days extracted at Bambidie are representative of a larger-scale cloud cover evolution in Western Central Africa, with a W-E gradient in the timing of afternoon cloud dissipation.

Sea level variability in Gulf of Guinea from satellite altimetry

Coastal zones with dense populations, low elevations and/or inadequate adaptive capacity are on the frontline of unprecedented impacts from climate change. The Gulf of Guinea (GoG), stretching from Liberia to Gabon, is in particular vulnerable to coastal flooding caused by local and/or climate-induced sea level rise. In this region, interannual to decadal coastal sea level changes remain poorly understood, mainly due to a lack of tide gauge stations. Here we use nearly three decades (1993–2021) of satellite altimetry data to study the link between the Equatorial Atlantic and coastal GoG sea level variability. The rate of mean sea level rise increased from 3.47 to 3.89 ± 0.10 mm/yr from the Equatorial oceanic domain to the GoG coastal area, with an acceleration of 0.094 ± 0.050 mm/yr2. This corresponds to a mean sea level rise of about 8.9 cm over the entire altimetry period, 1993–2021. We focus on the (extreme) warm/cold events that occur in both the GoG during Atlantic Niños, and along the Angola-Namibia coast during Benguela Niños. Both events are driven by remote forcing via equatorial Kelvin waves and local forcing by local winds, freshwater fluxes and currents intensifications. Analysis of altimetry-based sea level, sea surface temperature anomalies, 20 °C isotherm based PIRATA moorings, and the Argo-based steric and thermometric sea level allows us to follow the coastal trapped waves (CTWs) along the GoG, and its link with major events observed along the strong Equatorial Atlantic warmings in 2010, 2012, 2019 and 2021. Both 2019 and 2021 warming have been identified as the warmest event ever reported in this region during the last 40 years. A lag of 1 month is observed between equatorial and West African coastal trapped wave propagation. This observation may help to better anticipate and manage the effects of extreme events on local ecosystems, fisheries, and socio-economic activities along the affected coastlines. In order to enable informed decision-making and guarantee the resilience of coastal communities in the face of climate change, it emphasises the significance of ongoing study in this field.

Discovery and Mechanistic Study of Novel Mycobacterium tuberculosis ClpP1P2 Inhibitors.

Caseinolytic protease P (ClpP) responsible for the proteolysis of damaged or misfolded proteins plays a critical role in proteome homeostasis. MtbClpP1P2, a ClpP enzyme complex, is required for survival in Mycobacterium tuberculosis, and it is therefore considered as a promising target for the development of antituberculosis drugs. Here, we discovered that cediranib and some of its derivatives are potent MtbClpP1P2 inhibitors and suppress M. tuberculosis growth. Protein pull-down and loss-of-function assays validated the in situ targeting of MtbClpP1P2 by cediranib and its active derivatives. Structural and mutational studies revealed that cediranib binds to MtbClpP1P2 by binding to an allosteric pocket at the equatorial handle domain of the MtbClpP1 subunit, which represents a unique binding mode compared to other known ClpP modulators. These findings provide us insights for rational drug design of antituberculosis therapies and implications for our understanding of the biological activity of MtbClpP1P2.

Saccharomyces cerevisiae survival against heat stress entails a communication between CCT and cell wall integrity pathway.

The chaperonin TRiC/CCT is cytosolic cylindrical complex of 16 subunits encoded by eight essential genes CCT1-8. It contributes to folding 10% of cellular polypeptides in yeast. The strain carrying substitution point mutation G412E in the equatorial domain of Cct7p resulted in the improper folding of substrates. In this study, the Cct7p mutant exhibited sensitivity to non-optimal growth temperatures and cell wall stressors. Heat shock is known to disrupt cell wall and protein stability in budding yeast. Mitogen-activated protein kinase-mediated cell wall integrity pathway gets activated to compensate the perturbed cell wall. Overexpression of the PKC1 and SLT2 genes of MAPK signaling pathway in mutant rescued the growth and cell division defects. Additionally, the genes of the CWI pathway such as SED1, GFA1, PIR1, and RIM21 are down-regulated. The Cct7p mutant strain (G412E) is unable to withstand the heat stress due to the underlying defects in protein folding and cell wall maintenance. Taken together, our results strongly indicate the interaction between CCT and cell wall integrity pathway.

Molecular Dynamics Mappings of the CCT/TRiC Complex-Mediated Protein Folding Cycle Using Diffracted X-ray Tracking.

The CCT/TRiC complex is a type II chaperonin that undergoes ATP-driven conformational changes during its functional cycle. Structural studies have provided valuable insights into the mechanism of this process, but real-time dynamics analyses of mammalian type II chaperonins are still scarce. We used diffracted X-ray tracking (DXT) to investigate the intramolecular dynamics of the CCT complex. We focused on three surface-exposed loop regions of the CCT1 subunit: the loop regions of the equatorial domain (E domain), the E and intermediate domain (I domain) juncture near the ATP-binding region, and the apical domain (A domain). Our results showed that the CCT1 subunit predominantly displayed rotational motion, with larger mean square displacement (MSD) values for twist (χ) angles compared with tilt (θ) angles. Nucleotide binding had a significant impact on the dynamics. In the absence of nucleotides, the region between the E and I domain juncture could act as a pivotal axis, allowing for greater motion of the E domain and A domain. In the presence of nucleotides, the nucleotides could wedge into the ATP-binding region, weakening the role of the region between the E and I domain juncture as the rotational axis and causing the CCT complex to adopt a more compact structure. This led to less expanded MSD curves for the E domain and A domain compared with nucleotide-absent conditions. This change may help to stabilize the functional conformation during substrate binding. This study is the first to use DXT to probe the real-time molecular dynamics of mammalian type II chaperonins at the millisecond level. Our findings provide new insights into the complex dynamics of chaperonins and their role in the functional folding cycle.

Cryo-EM of a heterogeneous biochemical fraction elucidates multiple protein complexes from a multicellular thermophilic eukaryote

Biomolecular complexes and their interactions govern cellular structure and function. Understanding their architecture is a prerequisite for dissecting the cell's inner workings, but their higher-order assembly is often transient and challenging for structural analysis. Here, we performed cryo-EM on a single, highly heterogeneous biochemical fraction derived from Chaetomium thermophilum cell extracts to visualize the biomolecular content of the multicellular eukaryote. After cryo-EM single-particle image processing, results showed that a simultaneous three-dimensional structural characterization of multiple chemically diverse biomacromolecules is feasible. Namely, the thermophilic, eukaryotic complexes of (a) ATP citrate-lyase, (b) Hsp90, (c) 20S proteasome, (d) Hsp60 and (e) UDP-glucose pyrophosphorylase were characterized. In total, all five complexes have been structurally dissected in a thermophilic eukaryote in a total imaged sample area of 190.64 μm2, and two, in particular, 20S proteasome and Hsp60, exhibit side-chain resolution features. The C. thermophilum Hsp60 near-atomic model was resolved at 3.46 Å (FSC = 0.143) and shows a hinge-like conformational change of its equatorial domain, highly similar to the one previously shown for its bacterial orthologue, GroEL. This work demonstrates that cryo-EM of cell extracts will greatly accelerate the structural analysis of cellular complexes and provide unprecedented opportunities to annotate architectures of biomolecules in a holistic approach.

Crystal structures of dimeric and heptameric mtHsp60 reveal the mechanism of chaperonin inactivation.

Mitochondrial Hsp60 (mtHsp60) plays a crucial role in maintaining the proper folding of proteins in the mitochondria. mtHsp60 self-assembles into a ring-shaped heptamer, which can further form a double-ring tetradecamer in the presence of ATP and mtHsp10. However, mtHsp60 tends to dissociate in vitro, unlike its prokaryotic homologue, GroEL. The molecular structure of dissociated mtHsp60 and the mechanism behind its dissociation remain unclear. In this study, we demonstrated that Epinephelus coioides mtHsp60 (EcHsp60) can form a dimeric structure with inactive ATPase activity. The crystal structure of this dimer reveals symmetrical subunit interactions and a rearranged equatorial domain. The α4 helix of each subunit extends and interacts with its adjacent subunit, leading to the disruption of the ATP-binding pocket. Furthermore, an RLK motif in the apical domain contributes to stabilizing the dimeric complex. These structural and biochemical findings provide new insights into the conformational transitions and functional regulation of this ancient chaperonin.

Oligomeric state and chaperon activity of Hsp60.

Heat-shock proteins are capable to exert their stabilizing action against biomolecules aggregation through different mechanisms, which are generally related to their molecular weight. Similar to its bacterial homologous GroEl, Hsp60 is known to work as a folding machine with the assistance of co-chaperonin Hsp10 and ATP. However, recent experimental evidence suggested an alternative mechanism exploited by Hsp60 towards aggregation prone molecules. Indeed, we already observed that Hsp60 stabilized Aβ40 against fibrillization in the absence of ATP by recruiting early small aggregates of Ab, Here we investigate the mechanism exerted by Hsp60 against the amyloid fibrillization in relation with its oligomeric structure. To this purpose, the monomeric or tetradecameric form of the protein were isolated and their effect on beta-amyloid aggregation was tested separately. The structural stability of the two forms of Hsp60 was also investigated by differential scanning calorimetry (DSC), Light Scattering and Circular Dichroism. Results shown that the monomeric form is less stable but more effective against amyloid fibrillization. A major functionality related to a less ordered and stable structure is a common treat of proteins having intrinsically disordered regions (IDR). In Hsp60 contacts between subunits in the equatorial domain have been recognized as the region of moonlighting character. Their exposure to the solvent confers to monomeric Hsp60 the ability to interact with amyloid molecules at a major extent than that due to the plain increase of the total protein surface.

Folding of the SARS‐CoV‐2 RNA Polymerase by the Cytosolic Chaperonin CCT

The ongoing Covid‐19 pandemic, caused by the highly transmissible SARS‐CoV‐2 virus, constitutes the worst global public health crisis of the past century. Although effective vaccines have been developed, administration has been slow, new variants continue to emerge, and there remains a lack of effective antivirals to treat severe cases. Thus, there remains a significant need to understand the mechanisms of SARS‐CoV‐2 infection and replication to identify new potential therapeutic targets. To this end, we investigated whether SARS‐CoV‐2 might depend on the host cell chaperone system, particularly the essential cytosolic chaperonin, CCT, to fold or assemble any of its proteins. CCT has previously been shown to be required for the replication of several other viruses including reoviruses and zika virus. We screened likely candidates among the SARS‐CoV‐2 proteins for co‐immunoprecipitation with CCT and identified an interaction with the RNA‐dependent RNA polymerase, Nsp12. To confirm Nsp12 was a substrate, we depleted cells of CCT, then transfected with Nsp12 and observed a 40% decrease in Nsp12 expression in CCT‐depleted cells compared to the control. This decrease is consistent with what we have observed for other known CCT substrates. Additionally, CCT‐depleted cells infected with live SARS‐CoV‐2 produced a 50% decrease in viral titer compared to controls, indicating that CCT is important for viral replication. A preliminary cryo‐EM structure of the Nsp12‐CCT complex shows a very large mass identifiable as Nsp12 inside of CCT that extends from the equatorial domains up and out through one of the two folding cavities. The structure stands to both reveal an important step in SARS‐CoV‐2 replication and to answer a long‐standing question regarding how CCT can accommodate very large substrates.

Cdna Cloning and Expression Analysis of Chaperonin Containing T-Complex Polypeptide 1-Alpha in the Pearl Oyster Pinctada maxima Exposed to Cold Stress

The complete cDNA sequence of chaperonin-containing T-complex polypeptide 1-alpha (CCT-alpha) gene of the pearl oyster Pinctada maxima was determined using rapid amplification of cDNA ends technique and characterized with bioinformatic analysis. Its expression profile in different organs and under cold stress was characterized using real-time quantitative polymerase chain reaction. Results revealed that the complete cDNA sequence of P. maxima CCT-alpha has 1,803 base pairs (bp), including a 1,608-bp open reading framework that codes 535 amino acids. The protein has three conservative functional domains: equatorial, apical, and intermediate domains. The equatorial domain is 20 amino acids shorter than that of other species, and contains the three signature sequences of CCT family protein. The CCT-alpha of P. maxima has nine conservative ATP-binding sites and six protein-binding sites, and has high homology with Aplysia californica (80.7%), Delia antiqua (77.4%), Danio rerio (77.1%), Xenopus laevis (76.7%), Gallus gallus (76.4%), and Homo sapiens (75.4%). The CCT-alpha shows tissue-specific expression profile in P. maxima, with expression levels higher in gill, mantle, and adductor muscle than in hepatopancreas and heart. Cold stress markedly increased mRNA contents of CCT-alpha in the organs of P. maxima, but different organs showed distinct cold stress response pattern. Chaperonin-containing T-complex polypeptide 1-alpha transcription in adductor muscle, hepatopancreas, and heart increased at 2 h, and reached peak values at 6 h, maintained high levels at 12 h, and significantly decreased at 24 h. The product in gill and mantle decreased at 2 h, began to increase at 6 h, and showed a large increase at 12 h, but reduced to below the initial level at 24 h.

Spatial Variation in Primary Production in the Eastern Indian Ocean

To examine the spatial pattern and controlling factors of the primary productivity (PP) of phytoplankton in the eastern Indian Ocean (EIO), deck-incubation carbon fixation (a 14C tracer technique) and the related hydrographic properties were measured at 15 locations during the pre-summer monsoon season (February–April 2017). There are knowledge gaps in the field observations of PP in the EIO. The estimated daily carbon production rates integrated over the photic zone ranged from 113 to 817 mgC m–2 d–1, with a mean of 522 mgC m–2 d–1. The mixed-layer integrated primary production (MLD-PP) ranged from 29.0 to 303.7 mgC m–2 d–1 (mean: 177.2 mgC m–2 d–1). The contribution of MLD-PP to the photic zone-integrated PP (PZI-PP) varied between 19 and 51% (mean: 36%). Strong spatial variability in the carbon fixation rates was found in the study region. Specifically, the surface primary production rates were relatively higher in the Bay of Bengal domain affected by riverine flux and lower in the equatorial domain owing to the presence of intermonsoonal Wyrtki jets, which were characterized by a depression of thermocline and nitracline. The PZI-PP exhibited a linear (positive) relationship with nutrient values, but with no significance, indicating a partial control of macronutrients and a light limitation of carbon fixation. As evident from the vertical profiles, the primary production process mainly occurred above the nitracline depth and at high photosynthetic efficiency. Phytoplankton (>5 μm), including dinoflagellates, Trichodesmium, coccolithophores, and dissolved nutrients, are thought to have been correlated with primary production during the study period. The measured on-deck biological data of our study allow for a general understanding of the trends in PP in the survey area of the EIO and can be incorporated into global primary production models.

Role of rotational radial magnetic advection in possible explaining a cycle with two peaks

• Double maximum of the 11-year solar cycle. • Turbulent effects of macroscopic magnetohydrodynamics. • Negative magnetic buoyancy. • Turbulent pumping of a large-scale magnetic field. • Reconstructing of the toroidal magnetic field of the Sun. To explain the observed phenomenon of 11-year sunspot cycle with two peaks, we draw attention to the possible role of the turbulent magnetic pumping effects in the solar convection zone (SCZ) at the reconstructing of the toroidal magnetic field that generates the sunspots. Turbulent radial pumping of magnetic field has both kinetic (diamagnetism) and magnetic (vertical advection) contributions. We take into account five physical processes for the combined magnetic reconstructing in deep layers of the SCZ. They are the Ω effect near the tachocline, magnetic buoyancy of the smoothed field, macroscopic diamagnetism, rotational magnetic advection, and deep equatorward meridional circulation. It is the effect of advection with taking into account Sun's rotation that plays a key role in the proposed scenario of magnetic reconstructing. We found that reconstructing of deep toroidal field develops differently in the near-polar and equatorial domains of the SCZ. In the lower half of the near-polar domain, two downward pumping effects (diamagnetism and advection) act against magnetic buoyancy and, as a result, they neutralize magnetic buoyancy and thereby block the toroidal field near the tachocline. At the same time, in the deep layers of the equatorial domain, the rotational advection due to the latitudinal convection anisotropy changes its direction to the opposite (from downward to upward), thereby helping magnetic buoyancy. As a result, this upward magnetic pumping here contributes to the transport of the toroidal field to the solar surface. We call this transport as first upward magnetic advection surge. It ensures a transfer of the deep strong fields to the surface in the latitudes belt of sunspots. Meanwhile, a deep equatorward meridional flow transports the blocked near pole toroidal field in the tachocline from high latitudes to low ones where are favourable conditions for floating up of the magnetic field. Here this belated field is transported upward to the solar surface (the second upward magnetic advection surge). Ultimately, two time-delayed upward magnetic surges may cause on the surface in the “royal zone” the first and second peaks of the sunspots cycle.

Structural basis for the structural dynamics of human mitochondrial chaperonin mHsp60

Human mitochondrial chaperonin mHsp60 is essential for mitochondrial function by assisting folding of mitochondrial proteins. Unlike the double-ring bacterial GroEL, mHsp60 exists as a heptameric ring that is unstable and dissociates to subunits. The structural dynamics has been implicated for a unique mechanism of mHsp60. We purified active heptameric mHsp60, and determined a cryo-EM structure of mHsp60 heptamer at 3.4 Å. Of the three domains, the equatorial domains contribute most to the inter-subunit interactions, which include a four-stranded β sheet. Our structural comparison with GroEL shows that mHsp60 contains several unique sequences that directly decrease the sidechain interactions around the β sheet and indirectly shorten β strands by disengaging the backbones of the flanking residues from hydrogen bonding in the β strand conformation. The decreased inter-subunit interactions result in a small inter-subunit interface in mHsp60 compared to GroEL, providing a structural basis for the dynamics of mHsp60 subunit association. Importantly, the unique sequences are conserved among higher eukaryotic mitochondrial chaperonins, suggesting the importance of structural dynamics for eukaryotic chaperonins. Our structural comparison with the single-ring mHsp60-mHsp10 shows that upon mHsp10 binding the shortened inter-subunit β sheet is restored and the overall inter-subunit interface of mHsp60 increases drastically. Our structural basis for the mHsp10 induced stabilization of mHsp60 subunit interaction is consistent with the literature that mHsp10 stabilizes mHsp60 quaternary structure. Together, our studies provide structural bases for structural dynamics of the mHsp60 heptamer and for the stabilizing effect of mHsp10 on mHsp60 subunit association.

Slowdown of Water Dynamics from the Top to the Bottom of the GroEL Cavity.

The GroE molecular chaperone system is a critical protein machine that assists the folding of substrate proteins in its cavity. Water in the cavity is suspected to play a role in substrate protein folding, but the mechanism is currently unknown. Herein, we report measurements of water dynamics in the equatorial and apical domains of the GroEL cavity in the apo and football states, using site-specific tryptophanyl mutagenesis as an intrinsic optical probe with femtosecond resolution combined with molecular dynamics simulations. We observed clearly different water dynamics in the two domains with a slowdown of the cavity water from the apical to equatorial region in the football state. The results suggest that the GroEL cavity provides a unique water environment that may facilitate substrate protein folding.

Chaperonin point mutation enhances cadmium endurance in Saccharomyces cerevisiae.

To study the effect of the mutation in conserved G412E in Cct7p subunit of CCT complex on its cellular fate. TriC/CCT is a dynamic multimeric protein that assists in protein folding in an energy-dependent manner. A point mutation in the ATP binding pocket in the equatorial domain of the Cct7p subunit delays the doubling time. The cell size was twice the wild type, and the formation of protein aggregates suggests disturbed folding of the proteins. Upon growing in stressful conditions of arsenous acid and cadmium chloride, the mutant was lethal in As3+ but grew well in Cd2+ with 10.5µg cadmium uptake mg-1 compared to the wild type. The increased expression of vacuole transporters YCF1 and BPT1 by ten-fold and two-fold in mutant indicates the metal transportation to the vacuole. CCT complex was vulnerable to the mutation in G412E in the Cct7p subunit of protein folding molecular machinery. Interestingly, already stressed cells provided robustness against oxidative stress and cadmium sequestration in the vacuole.

Evaluating the segmented post-rift stratigraphic architecture of the Guyanas continental margin

Segmentation of the Guyanas continental margin of South America is inherited from the dual-phase Mesozoic rifting history controlling the first-order post-rift sedimentary architecture. The margin is divided into two segments by a transform marginal plateau (TMP), the Demerara Rise, into the Central and Equatorial Atlantic domains. This paper investigates the heterogeneities in the post-rift sedimentary systems at a mega-regional scale (>1000 km). Re-sampling seven key exploration wells and scientific boreholes provides new data (189 analysed samples) that have been used to build a high-resolution stratigraphic framework using multiple biostratigraphic techniques integrated with organic geochemistry to refine the timing of 10 key stratigraphic surfaces and three megasequences. The results have been used to calibrate the interpretation of a margin-scale two-dimensional seismic reflection dataset, and to build megasequence isochore maps, structural restorations and gross depositional environment maps at key time intervals of the margin evolution. Our findings revise the dating of the basal succession drilled by the A2-1 well, indicating that the oldest post-rift sequence penetrated along the margin is late Tithonian age (previously Callovian). Early Central Atlantic carbonate platform sediments passively infilled subcircular-shaped basement topography controlled by the underlying basement structure of thinned continental crust. Barremian–Aptian rifting in the Equatorial Atlantic, caused folding and thrusting of the Demerara Rise, resulting in major uplift, gravitational margin collapse, transpressional structures and peneplanation of up to 1 km of sediment capped by the regional angular Base Albian Unconformity. Equatorial Atlantic rifting led to margin segmentation and the formation of the TMP, where two major unconformities developed during the intra Late Albian and base Cenomanian. These two unconformities are time synchronous with oceanic crust accretion offshore French Guiana and in the Demerara–Guinea transform, respectively. A marine connection between the Central and Equatorial Atlantic is demonstrated by middle Late Albian times, coinciding with deposition of the organic-rich source rock of the Canje Formation (average total organic carbon 4.21%). The succession is variably truncated by the Middle Campanian Unconformity. Refining the stratigraphic framework within the context of the structural evolution and segmentation of the Guyanas margin impacts the understanding of key petroleum system elements. Supplementary material : Photographs of sandstone petrography thin sections (Fig. S1); calcareous nannofossil plates (Fig. S2); palynology reports for A2-1 and FG2-1 (Fig. S3); taxonomy description of new species; sample table and organic geochemistry results (Table S1); and nannofossil distribution charts (Table S2) are available at https://doi.org/10.6084/m9.figshare.c.5280490

Crystal structure of P. falciparum Cpn60 bound to ATP reveals an open dynamic conformation before substrate binding

Plasmodium falciparum harbors group 1 and group 2 chaperonin systems to mediate the folding of cellular proteins in different cellular locations. Two distinct group 1 chaperonins operate in the organelles of mitochondria and apicoplasts, while group 2 chaperonins function in the cytosol. No structural information has been reported for any chaperonin from plasmodium. In this study, we describe the crystal structure of a double heptameric ring Plasmodium falciparum mitochondrial chaperonin 60 (Cpn60) bound with ATP, which differs significantly from any known crystal structure of chaperonin 60. The structure likely represents a unique intermediate state during conformational conversion from the closed state to the opened state. Three of the seven apical domains are highly dynamic while the equatorial domains form a stable ring. The structure implies large movements of the apical domain in the solution play a role in nucleotide-dependent regulation of substrate binding and folding. A unique 26–27 residue insertion in the equatorial domain of Plasmodium falciparum mitochondrial chaperonin greatly increases both inter-ring and intra-ring subunit–subunit interactions. The present structure provides new insights into the mechanism of Cpn60 in chaperonin assembly and function.

Terrestrial palaeofloral succession across the Permian–Triassic Boundary in the North and South China blocks: a brief review

This paper critically reviews the Lopingian (Late Permian) to Early Triassic palaeofloral successions on both the South and North China blocks. From the Late Cisuralian (Early Permian) to the middle of the Lopingian, North and South China, both located in the equatorial domain, sheltered a homogeneous ‘Cathaysian Palaeoflora’ resulting from a Cisuralian southern extension and diversification from the Northern “cradle” of Cathaysian plants to the South. We analyse the progressive changes in the two regional floral successions due to environmental changes resulting from the northward drifting of the North China block while the South China block remained in the sub-equatorial domain. In the framework of our recent fieldwork in North China for Lopingian to Early Triassic fossil plant-bearing deposits, the very recent discovery of a new, rich fossiliferous locality allowed us to improve our knowledge of the Lopingian palaeofloral content and its palaeoenvironmental implications. The first steps of the post-Permian–Triassic boundary floral recovery can now be more accurately compared after the northward Lopingian migration of the North China block.

Isotropic High-Order Filter for a Local Domain on the Sphere

High-order filtering with isotropy of a local-domain data defined at an arbitrary location on the sphere, with an application to scale-decomposition of mean sea level pressure field, was investigated. The equation of high-order filter was based on the implicit hyper-diffusion of 8th-order, which was discretized by the Fourier-finite element method (FFEM). In order to apply the FFEM high-order filter to a local-domain data which is not represented with two-dimensional array, a rotation of coordinates was performed. The geometry of the rotated local domain was made to be either a polar cap (polar cap domain) or a symmetric window with respect to the Equator (Equatorial symmetric domain) to reduce the anisotropy of the local domains caused by the metric effect of spherical coordinates. The rotated local domains are extended by padding artificial data to match the boundary condition of vanishing gradient. The performance of the filters for the symmetric- or asymmetric- domain, was compared for both initial fields defined with an analytic function and the observed meteorological data. It turned out that the filters on the local domains with symmetry, i.e., the polar cap domain and the Equatorial symmetric domain, produced improved results over the local domains with asymmetry: Asymmetric error pattern between the northern and southern boundary, which is typical of the window domain defined on the middle latitude (or between the pole and the Equator), is reduced appreciably and the improvement is shown to become more significant for the window-domain closer to the pole. Through tests with wind fields, the performance of the filters on the polar cap domain and the Equatorial symmetric domain was found comparable to each other. The advantage of polar cap filter, being not available for the Equatorial symmetric domain filter, was illustrated by conducting a scale decomposition and composite analysis of the mean sea level pressure that requires the data manipulations such as a zonal averaging as well as azimuthal-phase shifting.