Ancient Mitogenomes Reveal the Evolutionary History and Biogeography of Sloths

1. Download : Download high-res image (298KB)
2. Download : Download full-size image

     

Using phylogeographic approaches to analyse the dispersal history,velocity and direction of viral lineages — Application to rabies virus spread in Iran

Recent years have seen the extensive use of phylogeographic approaches to unveil the dispersal history of virus epidemics. Spatially explicit reconstructions of viral spread represent valuable sources of lineage movement data that can be exploited to investigate the impact of underlying environmental layers on the dispersal of pathogens. Here, we performed phylogeographic inference and applied different post hoc approaches to analyse a new and comprehensive data set of viral genomes to elucidate the dispersal history and dynamics of rabies virus (RABV) in Iran, which have remained largely unknown. We first analysed the association between environmental factors and variations in dispersal velocity among lineages. Second, we present, test and apply a new approach to study the link between environmental conditions and the dispersal direction of lineages. The statistical performance (power of detection, false‐positive rate) of this new method was assessed using simulations. We performed phylogeographic analyses of RABV genomes, allowing us to describe the large diversity of RABV in Iran and to confirm the cocirculation of several clades in the country. Overall, we estimate a relatively high lineage dispersal velocity, similar to previous estimates for dog rabies virus spread in northern Africa. Finally, we highlight a tendency for RABV lineages to spread in accessible areas associated with high human population density. Our analytical workflow illustrates how phylogeographic approaches can be used to investigate the impact of environmental factors on several aspects of viral dispersal dynamics.     

Inhibition of polypeptide N-acetyl-α-galactosaminyltransferases is an underlying mechanism of dietary polyphenols preventing colorectal tumorigenesis

Ellagitannin-derived ellagic acid (EA) and colonic metabolite urolithins are functional dietary ingredients for cancer prevention, but the underlying mechanism need elucidation. Mucin-type O-glycosylation, initiated by polypeptide N-acetyl-α-galactosaminyltransferases (ppGalNAc-Ts), fine-tunes multiple biological processes and is closely associated with cancer progression. Herein, we aim to explore how specific tannin-based polyphenols affect tumor behavior of colorectal cancer cells (CRC) by modulating O-glycosylation. Utilizing HPLC-based enzyme assay, we find urolithin D (UroD), EA and gallic acid (GA) potently inhibit ppGalNAc-Ts. In particular, UroD inhibits ppGalNAc-T2 through a peptide/protein-competitive manner with nanomolar affinity. Computational simulations combined with site-directed mutagenesis further support the inhibitors’ mode of action. Moreover, lectin analysis and metabolic labelling reveal that UroD can reduce cell O-glycans but not N-glycans. Transwell experiments prove that UroD inhibits migration and invasion of CRC cells. Our work proves that specific tannin-based polyphenols can potently inhibit ppGalNAc-Ts activity to reduce cell O-glycosylation and lead to lowering the migration and invasion of CRC cells, suggesting that disturbance of mucin-type O-glycosylation is an important mechanism for the function of dietary polyphenols.     

Tuning surface‐cross‐linking of molecularly imprinted cross‐linked micelles for molecular recognition in water

Molecular recognition in water is an important challenge in supramolecular chemistry. Surface‐core double cross‐linking of template‐containing surfactant micelles by the click reaction and free radical polymerization yields molecularly imprinted nanoparticles (MINPs) with guest‐complementary binding sites. An important property of MINP‐based receptors is the surface‐cross‐linking between the propargyl groups of the surfactants and a diazide cross‐linker. Decreasing the number of carbons in between the two azides enhanced the binding affinity of the MINPs, possibly by keeping the imprinted binding site more open prior to the guest binding. The depth of the binding pocket can be controlled by the distribution of the hydrophilic/hydrophobic groups of the template and was found to influence the binding in addition to electrostatic interactions between oppositely charged MINPs and guests. Cross‐linkers with an alkoxyamine group enabled two‐stage double surface‐cross‐linking that strengthened the binding constants by an order of magnitude, possibly by expanding the binding pocket of the MINP into the polar region. The binding selectivity among very similar isomeric structures also improved.     

Multispectroscopic exploration and molecular docking analysis on interaction of eriocitrin with bovine serum albumin

Eriocitrin is a flavanone glycoside, which exists in lemon or lime citrus fruits. It possesses antioxidant, anticancer, and anti‐allergy activities. In order to investigate the pharmacokinetics and pharmacological mechanisms of eriocitrin in vivo, the interaction between eriocitrin and bovine serum albumin (BSA) was studied under the simulated physiological conditions by multispectroscopic and molecular docking methods. The results well indicated that eriocitrin and BSA formed a new eriocitrin‐BSA complex because of intermolecular interactions, which was demonstrated by the results of ultraviolet‐visible (UV‐vis) absorption spectra. The intrinsic fluorescence of BSA was quenched by eriocitrin, and static quenching was the quenching mechanism. The number of binding sites (n) and binding constant (K_b) at 310 K were 1.22 and 2.84 × 10⁶ L mol^?1, respectively. The values of thermodynamic parameters revealed that the binding process was spontaneous, and the main forces were the hydrophobic interaction. The binding distance between eriocitrin and BSA was 3.43 nm. In addition, eriocitrin changed the conformation of BSA, which was proved by synchronous fluorescence and circular dichroism (CD) spectra. The results of site marker competitive experiments suggested that eriocitrin was more likely to be inserted into the subdomain IIA (site I), which was further certified by molecular docking studies.     

pH‐dependent conformational dynamics of beta‐secretase 1: A molecular dynamics study

Beta‐secretase 1 (BACE‐1) is an aspartyl protease implicated in the overproduction of β‐amyloid fibrils responsible for Alzheimer disease. The process of β‐amyloid genesis is known to be pH dependent, with an activity peak between solution pH of 3.5 and 5.5. We have studied the pH‐dependent dynamics of BACE‐1 to better understand the pH dependent mechanism. We have implemented support for graphics processor unit (GPU) accelerated constant pH molecular dynamics within the AMBER molecular dynamics software package and employed this to determine the relative population of different aspartyl dyad protonation states in the pH range of greatest β‐amyloid production, followed by conventional molecular dynamics to explore the differences among the various aspartyl dyad protonation states. We observed a difference in dynamics between double‐protonated, mono‐protonated, and double‐deprotonated states over the known pH range of higher activity. These differences include Tyr 71‐aspartyl dyad proximity and active water lifetime. This work indicates that Tyr 71 stabilizes catalytic water in the aspartyl dyad active site, enabling BACE‐1 activity.     

Targeting metabolic pathways proteins of Orientia tsutsugamushi using combined hierarchical approach to combat scrub typhus

Orientia tsutsugamushi (Ott) is a causative agent of chigger‐borne zoonosis, scrub typhus which is life threatening and highly pervasive illness in humans. In this report, we have mined and classified the proteins involved in pathways unique to Ott by using high‐throughput computational techniques. The 12 metabolic pathways were found to be unique to the pathogen. Forty‐six proteins were reported to be essential for the pathogen's survival and non‐homologous to the humans. The proteins were categorized into different classes, ie, enzymes, transporters, DNA‐binding, secretory, and outer membrane proteins. Further, in silico analysis of 46 proteins showed that 25 proteins were suitable therapeutic targets with known druggable properties. The structural modeling of B3CSG3 (MurA) protein was carried out and catalytic site essential for its functioning was analyzed. Virtual screening of chemical compounds was performed against modeled structure. The docking study by AutodockVina reported compound from PubChem with CID: 16036947 as best and potential inhibitor by means of docking score and binding affinity. The reliability and stability of the MurA‐16036947 complex were confirmed with molecular dynamics simulation. The report will provide insight to understand the mechanism of pathogenesis of Ott and instigate the development of effective treatment strategies against this disease.     

Molecular dynamics simulation on the allosteric analysis of the c‐di‐GMP class I riboswitch induced by ligand binding

Riboswitches are RNA molecules that regulate gene expression using conformation change, affected by binding of small molecule ligands. Although a number of ligand‐bound aptamer complex structures have been solved, it is important to know ligand‐free conformations of the aptamers in order to understand the mechanism of specific binding by ligands. In this paper, we use dynamics simulations on a series of models to characterize the ligand‐free and ligand‐bound aptamer domain of the c‐di‐GMP class I (GEMM‐I) riboswitch. The results revealed that the ligand‐free aptamer has a stable state with a folded P2 and P3 helix, an unfolded P1 helix and open binding pocket. The first Mg ions binding to the aptamer is structurally favorable for the successive c‐di‐GMP binding. The P1 helix forms when c‐di‐GMP is successive bound. Three key junctions J1/2, J2/3 and J1/3 in the GEMM‐I riboswitch contributing to the formation of P1 helix have been found. The binding of the c‐di‐GMP ligand to the GEMM‐I riboswitch induces the riboswitch's regulation through the direct allosteric communication network in GEMM‐I riboswitch from the c‐di‐GMP binding sites in the J1/2 and J1/3 junctions to the P1 helix, the indirect ones from those in the J2/3 and P2 communicating to P1 helix via the J1/2 and J1/3 media.     

Ensuring quality in cervical screening programmes based on molecular human papillomavirus testing

The increased use of human papillomavirus testing within cervical screening programmes necessarily brings about changes to the laboratory services required to support them. A crucial element of such services is to demonstrate initial and ongoing quality of the test (and associated processes). In this review, we outline some of the quality considerations and challenges with an emphasis on the laboratory including assay and platform validation, internal quality control selection and strengths and weaknesses of external quality assurance schemes. The influence and role of key external entities, including regulatory agencies, guideline groups, programme commissioners and commercial providers, are also discussed.