Three-Finger Toxins from Brazilian Coral Snakes: From Molecular Framework to Insights in Biological Function

Studies on 3FTxs around the world are showing the amazing diversity in these proteins both in structure and function. In Brazil, we have not realized the broad variety of their amino acid sequences and probable diversified structures and targets. In this context, this work aims to conduct an in silico systematic study on available 3FTxs found in Micrurus species from Brazil. We elaborated a specific guideline for this toxin family. First, we grouped them according to their structural homologue predicted by HHPred server and further curated manually. For each group, we selected one sequence and constructed a representative structural model. By looking at conserved features and comparing with the information available in the literature for this toxin family, we managed to point to potential biological functions. In parallel, the phylogenetic relationship was estimated for our database by maximum likelihood analyses and a phylogenetic tree was constructed including the homologous 3FTx previously characterized. Our results highlighted an astonishing diversity inside this family of toxins, showing some groups with expected functional similarities to known 3FTxs, and pointing out others with potential novel roles and perhaps structures. Moreover, this classification guideline may be useful to aid future studies on these abundant toxins.

A pocket guide on how to structure SARS-CoV-2 drugs and therapies

The race to identify a successful treatment for COVID19 will be defined by fundamental research into the replication cycle of the SARS-CoV-2 virus. This has identified five distinct stages from which numerous vaccination and clinical trials have emerged alongside an innumerable number of drug discovery studies currently in development for disease intervention. Informing every step of the viral replication cycle has been an unprecedented ‘call-to-arms' by the global structural biology community. Of the 20 main SARS-CoV-2 proteins, 13 have been resolved structurally for SARS-CoV-2 with most having a related SARS-CoV and MERS-CoV structural homologue totalling some 300 structures currently available in public repositories. Herein, we review the contribution of structural studies to our understanding of the virus and their role in structure-based development of therapeutics.

The Functioning of Na+-ATPases from Protozoan Parasites: Are These Pumps Targets for Antiparasitic Drugs?

The ENA ATPases (from exitus natru: the exit of sodium) belonging to the P-type ATPases are structurally very similar to the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA); they exchange Na+ for H+ and, therefore, are also known as Na+-ATPases. ENA ATPases are required in alkaline milieu, as in the case for Aspergillus, where other transporters cannot mediate an uphill Na+ efflux. They are also important for salt tolerance, as described for Arabidopsis. During their life cycles, protozoan parasites might encounter a high pH environment, thus allowing consideration of ENA ATPases as possible targets for controlling certain severe parasitic diseases, such as Chagas’ Disease. Phylogenetic analysis has now shown that, besides the types IIA, IIB, IIC, and IID P-type ATPases, there exists a 5th subgroup of ATPases classified as ATP4-type ATPases, found in Plasmodium falciparum and Toxoplasma gondii. In malaria, for example, some drugs targeting PfATP4 destroy Na+ homeostasis; these drugs, which include spiroindolones, are now in clinical trials. The ENA P-type (IID P-type ATPase) and ATP4-type ATPases have no structural homologue in mammalian cells, appearing only in fungi, plants, and protozoan parasites, e.g., Trypanosoma cruzi, Leishmania sp., Toxoplasma gondii, and Plasmodium falciparum. This exclusivity makes Na+-ATPase a potential candidate for the biologically-based design of new therapeutic interventions; for this reason, Na+-ATPases deserves more attention.

Reflections on the Structural-Functional Evolution of the Hippocampus: What Is the Big Deal about a Dentate Gyrus

The vertebrate hippocampal formation has been central in discussions of comparative cognition, nurturing an interest in understanding the evolution of variation in hippocampal organization among vertebrate taxa and the functional consequences of that variation. Assuming some similarity between the medial pallium of extant amphibians and the hippocampus of stem tetrapods, we propose the hypothesis that the hippocampus of modern amniotes began with a medial pallium characterized by a relatively undifferentiated cytoarchitecture, more direct thalamic and olfactory sensory inputs, and a broad role in associative learning and memory processes that nonetheless included the map-like representation of space. From this modest beginning evolved the cognitively more specialized hippocampal formation of birds and the hippocampus of mammals with its confounding dentate gyrus. Much has been made of trying to identify a dentate homologue in birds, but there are compelling reasons to believe no such structural homologue/functional equivalent exists. The uniqueness of the mammalian dentate then raises the question of what might be the functional consequences of a hippocampus with a dentate compared to one without. One might be tempted to speculate that the presence of a dentate gyrus facilitates so-called pattern separation, but birds with their suspected dentate-less hippocampus display excellent hippocampal-dependent pattern separation relying on space. Perhaps one consequence of a dentate is a hippocampus better designed to process a broader array of stimuli beyond space to more robustly support episodic memory. What is clear is that any meaningful reconstruction of hippocampal evolution and the eventual identification of any subdivisional homologies will require more data on the neurobiological and functional properties of the nonmammalian hippocampus, particularly those of amphibians and reptiles.

Structure of the bovine COPI δ subunit μ homology domain at 2.15 Å resolution

The heptameric COPI coat (coatomer) plays an essential role in vesicular transport in the early secretory system of eukaryotic cells. While the structures of some of the subunits have been determined, that of the δ-COP subunit has not been reported to date. The δ-COP subunit is part of a subcomplex with structural similarity to tetrameric clathrin adaptors (APs), where δ-COP is the structural homologue of the AP μ subunit. Here, the crystal structure of the μ homology domain (MHD) of δ-COP (δ-MHD) obtained by phasing using a combined SAD–MR method is presented at 2.15 Å resolution. The crystallographic asymmetric unit contains two monomers that exhibit short sections of disorder, which may allude to flexible regions of the protein. The δ-MHD is composed of two subdomains connected by unstructured linkers. Comparison between this structure and those of known MHD domains from the APs shows significant differences in the positions of specific loops and β-sheets, as well as a more general change in the relative positions of the protein subdomains. The identified difference may be the major source of cargo-binding specificity. Finally, the crystal structure is used to analyze the potential effect of the I422T mutation in δ-COP previously reported to cause a neurodegenerative phenotype in mice.

Inhibition Of Anti-b2GPI-Dependent Thrombus Enhancement In The Laser-Induced Thrombosis Model In Mice

B2GPI is the major antigen for pathogenic antibodies in antiphospholipid syndrome (APS). The presence of anti-b2GPI antibodies correlates with increased risk for thrombosis and pregnancy loss in patients with APS. In animal models of thrombosis, anti-b2GPI antibodies cause the increase in thrombus size after injury to the vessel wall. We engineered a molecule, A1-A1, that prevents the binding of b2GPI to anionic phospholipids and ApoER2, and studied how it inhibits prothrombotic properties of anti-b2GPI antibodies in vivo using the laser-induced arterial thrombosis model. Lupus-prone (NZWxBXSB)F1 male mice express chronic autoimmune anti-b2GPI antibodies. In (NZWxBXSB)F1 mice, infusion of A1-A1 at a dose of 4 ug/g of body weight caused a decrease in thrombus size of more than 85% as compared to thrombus size in the absence of A1-A1. Similarly, A1-A1 inhibits prothrombotic properties of b2GPI/anti-b2GPI antibody complexes in wild type mice following acute infusion with anti-b2GPI positive APS IgG. The thrombus reduction was due to the binding of A1-A1 to b2GPI, because infusion of LA6, a structural homologue of A1 that does not bind b2GPI, did not affect thrombus size. We did not observe thrombus inhibition by A1-A1 in the absence of anti-b2GPI antibodies, indicating that A1-A1 does not affect normal thrombus formation in the absence of anti-b2GPI antibodies. Disclosures: No relevant conflicts of interest to declare.

σX Is Involved in Controlling Bacillus subtilis Biofilm Architecture through the AbrB Homologue Abh

ABSTRACT A characteristic feature of biofilm formation is the production of a protective extracellular polymeric matrix. In the gram-positive bacterium Bacillus subtilis, the biofilm matrix is synthesized by the products of the epsABCDEFGHIJKLMNO operon (hereafter called the eps operon) and yqxM-sipW-tasA loci. Transcription from these operons is repressed by two key regulators, AbrB and SinR. Relief of inhibition is necessary to allow biofilm formation to proceed. Here we present data indicating that Abh, a sequence and structural homologue of AbrB, regulates biofilm architecture by B. subtilis when colony morphology and pellicle formation are assessed. Data indicating that abh expression is dependent on the environmental signals that stimulate the activity of the extracytoplasmic function σ-factor σX are shown. We demonstrate that expression of slrR, the proposed activator of yqxM transcription, is positively controlled by Abh. Furthermore, Abh is shown to activate transcription from the promoter of the ep s operon through its control of SlrR. These findings add to the increasingly complex transcriptional network that controls biofilm formation by B. subtilis.