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Although several filoviruses are dangerous human pathogens, there is conflicting evidence regarding their origins and interactions with animal hosts. Here we attempt to improve this understanding using the paleoviral record over a geological time scale, protein structure predictions, tests for evolutionary maintenance, and phylogenetic methods that alleviate sources of bias and error. We found evidence for long branch attraction bias in the L gene tree for filoviruses, and that using codon-specific models and protein structural comparisons of paleoviruses ameliorated conflict and bias. We found evidence for four ancient filoviral groups, each with extant viruses and paleoviruses with open reading frames. Furthermore, we found evidence of repeated transfers of filovirus-like elements to mouse-like rodents. A filovirus-like nucleoprotein ortholog with an open reading frame was detected in three subfamilies of spalacid rodents (present since the Miocene). We provide evidence that purifying selection is acting to maintain amino acids, protein structure and open reading frames in these elements. Our finding of extant viruses nested within phylogenetic clades of paleoviruses informs virus discovery methods and reveals the existence of Lazarus taxa among RNA viruses. Our results resolve a deep conflict in the evolutionary framework for filoviruses and reveal that genomic transfers to vertebrate hosts with potentially functional co-options have been more widespread than previously appreciated. Author summary: Filoviruses are a family of RNA viruses discovered in 1967 and notorious for spillover of the dangerous pathogens, Ebola virus and Marburg virus. However, their origins, deeper relations, diversity, and interactions with animal hosts remain controversial. Part of the confusion may be that differing rates of evolution among divergent viral lineages can create a bias termed long branch attraction (LBA). We tested for this scenario in the L protein gene sequence of filoviruses and found evidence that LBA is occurring leading to a false pairing of filovirus lineages associated with a fish and a snake. We found that using nucleotides instead of amino acids when inferring trees, paleoviral sequences with open reading frames, additional conserved genes, and comparisons of predicted protein structures can resolve the LBA. We found four major groups of filoviruses, with the paleoviral record and trees being consistent with an ancient fish origin for the family. Moreover, we found evidence of a filovirus-like element in spalacid rodents that has been evolutionarily maintained at the open-reading frame, amino acid sequence and structural level for over 20 million years. We conclude that genomic interactions of filoviruses with vertebrates likely predates the separation of lobe-finned and ray-finned fish and that filoviral elements (including potential co-opted genes) are more widespread than previously appreciated. [ABSTRACT FROM AUTHOR]

The shelterin complex is a macromolecular assembly of proteins that binds to and protects telomeric DNA, which composes the ends of all linear chromosomes. Shelterin proteins prevent chromosome ends from fusing together and from eliciting erroneous induction of DNA damage response pathways. In addition, shelterin proteins play key roles in regulating the recruitment and activation of telomerase, an enzyme that extends telomeric DNA. In fission yeast, Schizosaccharomyces pombe, interactions between the shelterin proteins Ccq1, Tpz1, and Poz1 are important for regulating telomerase-mediated telomere synthesis and thus telomere length homeostasis. Here, we used electron microscopy combined with genetic labeling to define the three-dimensional arrangement of the S. pombe Ccq1-Tpz1-Poz1 (CTP) complex. Crosslinking mass spectrometry was used to identify individual residues that are in proximity to the protein-protein interfaces of the assembled CTP complex. Together, our data provide a first glimpse into the architectural design of the CTP complex and reveals unique interactions that are important in maintaining the S. pombe telomere in a non-extendible state.

Telomeres are specialized nucleoprotein complexes that comprise the ends of linear chromosomes. Human telomeres end in a short, single-stranded DNA (ssDNA) overhang that is recognized and bound by two telomere proteins, POT1 and TPP1. Whereas POT1 binds directly to telomere ssDNA, its interaction with TPP1 is essential for localization of POT1 to the telomere. TPP1 also provides enhanced binding and sequence discrimination that regulates POT1-TPP1 interactions exclusively with telomere ssDNA. Finally, TPP1 recruits telomerase, the enzyme responsible for synthesis of telomere DNA, to the telomere. While the oligosaccharide-oligonucleotide-binding (OB)-fold domain of TPP1 has been solved by X-ray crystallography, the molecular interactions within the POT1-TPP1-ssDNA ternary complex and the conformational changes that contribute to its diverse functions remain ambiguous. We employed hydrogen/deuterium exchange combined with mass spectrometry to identify three peptides, all residing within the OB-fold of TPP1, that exhibit altered exchange rates upon complex formation or ssDNA binding. Mutation of these regions combined with functional assays revealed the diverse contributions of each moiety in protein-protein interactions, regulating telomerase activity or DNA-binding. Together, these functional data combined with biophysical analyses and homology modeling provide a molecular understanding of the diverse contributions of TPP1 in telomere maintenance.

This study investigates the influence of fibre orientation and heat flux on the post‐fire (residual) load‐bearing properties of carbon fibre‐reinforced polymer (CFRP) laminates. As a result, a deep insight into the post‐fire load‐bearing response is gained, which is necessary to fully understand and assess the advantages of CFRP laminates containing different fibre orientations for use in load‐bearing structures. Specimens were produced from three CFRP laminates containing different fibre orientations, exposed to varying heat fluxes up to 40 kW/m2 and then loaded in either tension or three‐point bending at ambient room temperature. The study's results have shown that the post‐fire behaviour of CFRP specimens is sensitive to changes in fibre orientation and heat flux. For example, specimens with an anisotropic fibre orientation in tension had the highest tensile load‐bearing capacity, whereas those with bidirectional and multi‐directional fibre orientations demonstrated lower tensile load‐bearing capacities. In bending, however, specimens containing bidirectional and multidirectional fibre orientations had higher load‐bearing capacities than specimens with an anisotropic fibre orientation. Furthermore, the data also shows that exposure to a heat flux reduces the load‐bearing capacity in both the bending and tensile specimens. [ABSTRACT FROM AUTHOR]