Carbohydrate-mediated interactions between chloroviruses and the immune system.

Understanding the molecular mechanisms which drive and modulate host-pathogen interactions are essential when designing effective therapeutic and diagnostic approaches aimed at controlling infectious diseases. Certain large and giant viruses have recently been discovered as components of the human virome, yet little is known about their interactions with the host immune system. We have dissected the role of viral N-linked glycans during the interaction between the glycoproteins from six chloroviruses (belonging to three chlorovirus classes: NC64A, SAG, and Osy viruses) and the representative carbohydrate-binding receptors of the innate immune system.

Unveiling the GT114 family: Structural characterization of A075L, a glycosyltransferase from Paramecium bursaria chlorella virus-1 (PBCV-1).

Protein A075L is a β-xylosyltransferase that participates in producing the core of the N-glycans found in VP54, the major viral capsid protein of Paramecium bursaria chlorella virus-1 (PBCV-1). In this study, we present an X-ray crystallographic analysis of the apo form of A075L, along with its complexes with the sugar donor and with a trisaccharide acceptor. The protein structure shows a typical GT-B folding, with two Rossmann-like fold domains, in which the acceptor substrate binds to the N-terminal region, and the nucleotide-sugar donor binds to the C-terminal region.

Genomics and evolutionary analysis of infecting viruses demarcate criteria for defining species of giant viruses.

Chloroviruses exhibit a close relationship with their hosts with the phenotypic aspect of their ability to form lytic plaques having primarily guided the taxonomy. However, with the isolation of viruses that are only able to complete their replication cycle in one strain of , systematic challenges emerged. In this study, we described the genomic features of 53 new chlorovirus isolates and used them to elucidate part of the evolutionary history and taxonomy of this clade.

Efficient assays to quantify the life history traits of algal viruses.

Viruses play a crucial role in microbial ecosystems by liberating nutrients and regulating the growth of their hosts. These effects are governed by viral life history traits, i.e.

Viral Chemotaxis of Paramecium Bursaria Altered by Algal Endosymbionts.

Chemotaxis is widespread across many taxa and often aids resource acquisition or predator avoidance. Species interactions can modify the degree of movement facilitated by chemotaxis. In this study, we investigated the influence of symbionts on Paramecium bursaria's chemotactic behavior toward chloroviruses.

Combination of hydrophobicity and codon usage bias determines sorting of model K channel protein to either mitochondria or endoplasmic reticulum.

When the K channel-like protein Kesv from Ectocarpus siliculosus virus 1 is heterologously expressed in mammalian cells, it is sorted to the mitochondria. This targeting can be redirected to the endoplasmic reticulum (ER) by altering the codon usage in distinct regions of the gene or by inserting a triplet of hydrophobic amino acids (AAs) into the protein's C-terminal transmembrane domain (ct-TMD). Systematic variations in the flavor of the inserted AAs and/or its codon usage show that a positive charge in the inserted AA triplet alone serves as strong signal for mitochondria sorting.

Viral DNA Accumulation Regulates Replication Efficiency of OSy-NE5 in Two Closely Related Strains.

Many chloroviruses replicate in algal strains that are ex-endosymbionts isolated from the protozoan including the NC64A and Syngen 2-3 strains. We noticed that indigenous water samples produced a higher number of plaque-forming viruses on Syngen 2-3 lawns than on NC64A lawns. These observed differences led to the discovery of viruses that replicate exclusively in Syngen 2-3 cells, named Only Syngen (OSy) viruses.

Lessons from Chloroviruses: the Complex and Diverse Roles of Viruses in Food Webs.

Viruses can have large effects on the ecological communities in which they occur. Much of this impact comes from the mortality of host cells, which simultaneously alters microbial community composition and causes the release of matter that can be used by other organisms. However, recent studies indicate that viruses may be even more deeply integrated into the functioning of ecological communities than their effect on nutrient cycling suggests.

Early-Phase Drive to the Precursor Pool: Chloroviruses Dive into the Deep End of Nucleotide Metabolism.

Viruses face many challenges on their road to successful replication, and they meet those challenges by reprogramming the intracellular environment. Two major issues challenging Paramecium bursaria chlorella virus 1 (PBCV-1, genus , family ) at the level of DNA replication are (i) the host cell has a DNA G+C content of 66%, while the virus is 40%; and (ii) the initial quantity of DNA in the haploid host cell is approximately 50 fg, yet the virus will make approximately 350 fg of DNA within hours of infection to produce approximately 1000 virions per cell. Thus, the quality and quantity of DNA (and RNA) would seem to restrict replication efficiency, with the looming problem of viral DNA synthesis beginning in only 60-90 min.

The consumption of viruses returns energy to food chains.

Viruses impact host cells and have indirect effects on ecosystem processes. Plankton such as ciliates can reduce the abundance of virions in water, but whether virus consumption translates into demographic consequences for the grazers is unknown. Here, we show that small protists not only can consume viruses they also can grow and divide given only viruses to eat.

Near-atomic, non-icosahedrally averaged structure of giant virus Paramecium bursaria chlorella virus 1.

Giant viruses are a large group of viruses that infect many eukaryotes. Although components that do not obey the overall icosahedral symmetry of their capsids have been observed and found to play critical roles in the viral life cycles, identities and high-resolution structures of these components remain unknown. Here, by determining a near-atomic-resolution, five-fold averaged structure of Paramecium bursaria chlorella virus 1, we unexpectedly found the viral capsid possesses up to five major capsid protein variants and a penton protein variant.

The Astounding World of Glycans from Giant Viruses.

Viruses are a heterogeneous ensemble of entities, all sharing the need for a suitable host to replicate. They are extremely diverse, varying in morphology, size, nature, and complexity of their genomic content. Typically, viruses use host-encoded glycosyltransferases and glycosidases to add and remove sugar residues from their glycoproteins.

Chlorovirus ATCV-1 Accelerates Motor Deterioration in SOD1-G93A Transgenic Mice and Its SOD1 Augments Induction of Inflammatory Factors From Murine Macrophages.

Background: Genetically polymorphic Superoxide Dismutase 1 G93A (SOD1-G93A) underlies one form of familial Amyotrophic Lateral Sclerosis (ALS). Exposures from viruses may also contribute to ALS, possibly by stimulating immune factors, such as IL-6, Interferon Stimulated Genes, and Nitric Oxide. Recently, chlorovirus ATCV-1, which encodes a SOD1, was shown to replicate in macrophages and induce inflammatory factors.

N-glycans from Paramecium bursaria chlorella virus MA-1D: Re-evaluation of the oligosaccharide common core structure.

Paramecium bursaria chlorella virus MA-1D is a chlorovirus that infects Chlorella variabilis strain NC64A, a symbiont of the protozoan Paramecium bursaria. MA-1D has a 339-kb genome encoding ca. 366 proteins and 11 tRNAs.

Catalysis of Chlorovirus Production by the Foraging of on Containing Endosymbiotic Algae.

Chloroviruses are large viruses that replicate in chlorella-like green algae and normally exist as mutualistic endosymbionts (referred to as zoochlorellae) in protists such as . Chlorovirus populations rise and fall in indigenous waters through time; however, the factors involved in these virus fluctuations are still under investigation. Chloroviruses attach to the surface of but cannot infect their zoochlorellae hosts because the viruses cannot reach the zoochlorellae as long as they are in the symbiotic phase.

Pursuit of chlorovirus genetic transformation and CRISPR/Cas9-mediated gene editing.

Genetic and molecular modifications of the large dsDNA chloroviruses, with genomes of 290 to 370 kb, would expedite studies to elucidate the functions of both identified and unidentified virus-encoded proteins. These plaque-forming viruses replicate in certain unicellular, eukaryotic chlorella-like green algae. However, to date, only a few of these algal species and virtually none of their viruses have been genetically manipulated due to lack of practical methods for genetic transformation and genome editing.

Functional Genomic Analyses Reveal an Open Pan-genome for the Chloroviruses and a Potential for Genetic Innovation in New Isolates.

Chloroviruses (family ) are large double-stranded DNA (dsDNA) viruses that infect unicellular green algae present in inland waters. These viruses have been isolated using three main chlorella-like green algal host cells, traditionally called NC64A, SAG, and Pbi, revealing extensive genetic diversity. In this study, we performed a functional genomic analysis on 36 chloroviruses that infected the three different hosts.

Towards an integrative view of virus phenotypes.

Understanding how phenotypes emerge from genotypes is a foundational goal in biology. As challenging as this task is when considering cellular life, it is further complicated in the case of viruses. During replication, a virus as a discrete entity (the virion) disappears and manifests itself as a metabolic amalgam between the virus and the host (the virocell).

Glacier ice archives nearly 15,000-year-old microbes and phages.

Background: Glacier ice archives information, including microbiology, that helps reveal paleoclimate histories and predict future climate change. Though glacier-ice microbes are studied using culture or amplicon approaches, more challenging metagenomic approaches, which provide access to functional, genome-resolved information and viruses, are under-utilized, partly due to low biomass and potential contamination.

Results: We expand existing clean sampling procedures using controlled artificial ice-core experiments and adapted previously established low-biomass metagenomic approaches to study glacier-ice viruses.

Codon Bias Can Determine Sorting of a Potassium Channel Protein.

Due to the redundancy of the genetic code most amino acids are encoded by multiple synonymous codons. It has been proposed that a biased frequency of synonymous codons can affect the function of proteins by modulating distinct steps in transcription, translation and folding. Here, we use two similar prototype K channels as model systems to examine whether codon choice has an impact on protein sorting.

Identification of a Chlorovirus PBCV-1 Protein Involved in Degrading the Host Cell Wall during Virus Infection.

Chloroviruses are unusual among viruses infecting eukaryotic organisms in that they must, like bacteriophages, penetrate a rigid cell wall to initiate infection. PBCV-1 infects its host, NC64A by specifically binding to and degrading the cell wall of the host at the point of contact by a virus-packaged enzyme(s). However, PBCV-1 does not use any of the five previously characterized virus-encoded polysaccharide degrading enzymes to digest the host cell wall during virus entry because none of the enzymes are packaged in the virion.

Sterol Biosynthesis in Four Green Algae: A Bioinformatic Analysis of the Ergosterol Versus Phytosterol Decision Point.

Animals and fungi produce cholesterol and ergosterol, respectively, while plants produce the phytosterols stigmasterol, campesterol, and β-sitosterol in various combinations. The recent sequencing of many algal genomes allows the detailed reconstruction of the sterol metabolic pathways. Here, we characterized sterol synthesis in two sequenced Chlorella spp.

Distinct lipid bilayer compositions have general and protein-specific effects on K+ channel function.

It has become increasingly apparent that the lipid composition of cell membranes affects the function of transmembrane proteins such as ion channels. Here, we leverage the structural and functional diversity of small viral K+ channels to systematically examine the impact of bilayer composition on the pore module of single K+ channels. In vitro-synthesized channels were reconstituted into phosphatidylcholine bilayers ± cholesterol or anionic phospholipids (aPLs).

Chlorovirus PBCV-1 Multidomain Protein A111/114R Has Three Glycosyltransferase Functions Involved in the Synthesis of Atypical N-Glycans.

The structures of the four -linked glycans from the prototype chlorovirus PBCV-1 major capsid protein do not resemble any other glycans in the three domains of life. All known chloroviruses and antigenic variants (or mutants) share a unique conserved central glycan core consisting of five sugars, except for antigenic mutant virus P1L6, which has four of the five sugars. A combination of genetic and structural analyses indicates that the protein coded by PBCV-1 gene , conserved in all chloroviruses, is a glycosyltransferase with three putative domains of approximately 300 amino acids each.