Novel Roles of G-quadruplexes on Enhancers in human chromatin

G-quadruplexes (G4), stable four-stranded non-canonical DNA structures, are highly related to function of promoters and initiation of gene transcription. We found that G4 structures were also enriched in the enhancers across different cell lines. However, the relationship between G4 structures and enhancer activity remains unknown. Here, we proved that G4 structures on enhancers lead to the re-positioning of nucleosomes create nucleosome depleted regions (NDRs). Moreover, stable NDRs and special secondary structures of G4 help enhancers to recruit abundant TFs to co-bind, especially for architectural proteins including CTCF, RAD21, and SMC3. These architectural proteins, which play critical roles in the formation of higher-order chromatin organization, further influenced the chromatin interactions of G4 enhancers. Additionally, we revealed that G4 enhancers harbored significantly higher enrichment of eQTLs than typical enhancers, suggesting G4 enhancers displayed more enhancer regulatory activity. We found that most super enhancers (SEs) contain G4 structures. Even though the enrichment of chromatin accessibility and histone modifications around G4-containing SEs are not significantly higher than those around other SEs, G4-containing SEs still possess much more TFs across different cell lines. According to these results, we proposed a model in which the formation of G4 structures on enhancer exclude nucleosome occupancy and recruit abundant TFs which lead to the stable chromatin interaction between G4 enhancers and their target genes. Because of the relevance between G4 structures and enhancers, we hypothesized that G4 structures may be a potential markers indicating enhancer regulatory activity.