The Essential Co-Option of Uracil-DNA Glycosylases by Herpesviruses Invites Novel Antiviral Design

Divergent structures of Mammalian and gammaherpesvirus uracil DNA glycosylases confer distinct DNA binding and substrate activity

Uracil DNA glycosylase (UNG) removes mutagenic uracil base from DNA to initiate base excision repair (BER). The result is an abasic site (AP site) that is further processed by the high-fidelity BER pathway to complete repair and maintain genome integrity. The gammaherpesviruses (GHVs), human Kaposi sarcoma herpesvirus (KSHV), Epstein-Barr virus (EBV), and murine gammaherpesvirus 68 (MHV68) encode functional UNGs that have a role in viral genome replication. Mammalian and GHVs UNG share overall structure and sequence similarity except for a divergent amino-terminal domain and a leucine loop motif in the DNA binding domain that varies in sequence and length. To determine if divergent domains contribute to functional differences between GHV and mammalian UNGs, we analyzed their roles in DNA interaction and catalysis. By utilizing chimeric UNGs with swapped domains we found that the leucine loop in GHV, but not mammalian UNGs facilitates interaction with AP sites and that the amino-terminal domain modulates this interaction. We also found that the leucine loop structure contributes to differential UDGase activity on uracil in single- versus double-stranded DNA. Taken together we demonstrate that the GHV UNGs evolved divergent domains from their mammalian counterparts that contribute to differential biochemical properties from their mammalian counterparts.

Circ-Udg Derived from Cyprinid Herpesvirus 2 Promotes Viral Replication

Cyprinid herpesvirus 2 (CyHV-2) has caused great losses to the gibel carp (Carassius auratus gibelio) industry. Previous studies showed that certain DNA viruses can encode circular RNAs (circRNAs) to regulate virus infection, which provides new clues for the treatment of viral disease. Whether CyHV-2 can encode circRNAs is still unknown. Here, 10 CyHV-2-derived circRNAs were identified, and the function of circ-udg, a circRNA derived from the CyHV-2 uracil DNA glycosylase (udg) gene, was studied. Although the expression level of circ-udg was lower than that of the parental gene, udg, its expression level was elevated in tandem with the proliferation of CyHV-2 and udg. In vitro experiments confirmed that circ-udg could promote the proliferation of CyHV-2. Moreover, circ-udg could encode a truncated UDG protein consisting of 147-amino-acid residues (termed circ-udg-P147). Both UDG and circ-udg-P147 were found to promote CyHV-2 proliferation, but the promoting effect of circ-udg on CyHV-2 proliferation was attenuated after circ-udg lost the ability to encode circ-udg-P147. Also, circ-udg-P147 could not change the transcription level of the udg gene. Interestingly, the UDG protein level was increased by circ-udg-P147. These results deepen the understanding of the genetic information carried by the genome of CyHV-2 and provide a new target for the treatment of gibel carp bleeding disease caused by CyHV-2. IMPORTANCE The outbreak of C. auratus gibelio gill hemorrhagic disease caused by CyHV-2 brought great losses to the gibel carp industry. Therefore, exploring the interaction between CyHV-2 and host and the molecular mechanism of viral infection is of great significance in preventing and treating the gibel carp gill hemorrhagic disease. Although some progress has been made in the study of CyHV-2, the mechanism of interaction between CyHV-2 and crucian carp is still unclear. In this study, we found that CyHV-2 can encode circRNA to regulate virus replication. Our study provides novel information on CyHV-2 functional genomics, a reference for research into the circRNA of other viruses, and theoretical guidance for preventing and treating gibel carp bleeding disease.

Genomes of Anguillid Herpesvirus 1 Strains Reveal Evolutionary Disparities and Low Genetic Diversity in the Genus Cyprinivirus

Anguillid herpesvirus 1 (AngHV-1) is a pathogen of eels and a member of the genus Cyprinivirus in the family Alloherpesviridae. We have compared the biological and genomic features of different AngHV-1 strains, focusing on their growth kinetics in vitro and genetic content, diversity, and recombination. Comparisons based on three core genes conserved among alloherpesviruses revealed that AngHV-1 exhibits a slower rate of change and less positive selection than other cypriniviruses. We propose that this may be linked to major differences in host species and corresponding epidemiological circumstances. Efforts to derive evolutionary rate estimates for cypriniviruses under various theoretical models were ultimately unrewarding. We highlight the potential value of future collaborative efforts towards generating short-term evolutionary rate estimates based on known sequence sampling dates. Finally, we revealed that there is significantly less genetic diversity in core gene sequences within cyprinivirus species clades compared to species in the family Herpesviridae. This suggests that cyprinivirus species may have undergone much more vigorous purifying selection post species clade divergence. We discuss whether this may be linked to biological and anthropogenic factors or to sampling bias, and we propose that the comparison of short-term evolutionary rates between species may provide further insights into these differences.

Nutraceutical Curcumin with Promising Protection against Herpesvirus Infections and Their Associated Inflammation: Mechanisms and Pathways

Herpesviruses are DNA viruses that infect humans and animals with the ability to induce latent and lytic infections in their hosts, causing critical health complications. The enrolment of nutraceutical anti-herpesvirus drugs in clinical investigations with promising levels of reduced resistance, free or minimal cellular toxicity, and diverse mechanisms of action might be an effective way to defeat challenges that hurdle the progress of anti-herpesvirus drug development, including the problems with drug resistance and recurrent infections. Therefore, in this review, we aim to hunt down all investigations that feature the curative properties of curcumin, a principal bioactive phenolic compound of the spice turmeric, in regard to various human and animal herpesvirus infections and inflammation connected with these diseases. Curcumin was explored with potent antiherpetic actions against herpes simplex virus type 1 and type 2, human cytomegalovirus, Kaposi’s sarcoma-associated herpesvirus, Epstein–Barr virus, bovine herpesvirus 1, and pseudorabies virus. The mechanisms and pathways by which curcumin inhibits anti-herpesvirus activities by targeting multiple steps in herpesvirus life/infectious cycle are emphasized. Improved strategies to overcome bioavailability challenges that limit its use in clinical practice, along with approaches and new directions to enhance the anti-herpesvirus efficacy of this compound, are also reviewed. According to the reviewed studies, this paper presents curcumin as a promising natural drug for the prevention and treatment of herpesvirus infections and their associated inflammatory diseases.