Genome-wide analysis reveals a regulatory role for G-quadruplexes during Adenovirus multiplication

The G-quadruplex (GQ) motifs have recently been gaining prominence because of their role as gene cis-regulatory elements in a variety of organisms and as potential druggable targets for anti-cancer therapy and ageing. Several studies have demonstrated the existence of GQs in the genomes of emerging and re-emerging human pathogens, such as hepatitis virus, herpesviruses, Ebola virus, Zika virus and Nipah virus. Human Adenovirus (HAdV) exhibits a large number of clinical manifestations especially infecting the children and the immunocompromised patients. Moreover, the HAdV-based vectors have been widely used to deliver foreign DNAs to cells in gene therapy. However, the DNA secondary structural elements in AdV-based vectors could significantly determine the gene delivery efficacy of the vectors. In this study, using a combination of whole genome sequence analysis, biochemical, biophysical and interaction assays, we revealed fifteen putative GQs that are conserved across the different species of HAdV. We further showed that the GQs are embedded in the sequences of essential viral genes, namely E1B, E2B, and L3 genes (among others), which are involved in the early and late stages of the viral life cycle. Notably, Braco-19 (a well-known GQ binding ligand) interacted specifically with the HAdV GQs and increased their stability and further blocked the HAdV multiplication in human cells. Taken together, our data strongly supported the existence of G-quadruplex structures in the HAdV genome that affect the virus multiplication and posit that such structures may influence the efficacy of the gene-delivery vectors or even the HAdV virus life-cycle.