The effect of carotenoids obtained from saffron on histone H1 structure and H1-DNA interaction

It is already known that transcriptional activation of genes occurs due to the H1 dissociation from linker DNA; hence, histone H1-DNA complex is considered as a model of chromatin. Anticancer property of saffron and its carotenoids has already been reported. The present study aimed at investigating the effect of saffron carotenoids on H1 structure and H1-DNA interaction as a possible mechanism of their anticarcinogenic action. After purification of the saffron carotenoids (crocin, crocetin and dimethylcrocetin), their interaction with histone H1 was studied using spectrophotometry and spectrofluorometry. Some changes on the absorption spectra of H1 indicated the complex formation between this protein and saffron carotenoids. Also, the fluorescence emission of H1 was quenched by the mentioned ligands. The binding parameters of all the three ligands were obtained through Schatchard analysis of the quenching data. Then, the effect of each ligand on the H1-DNA interaction was studied. The results showed a shift in the precipitation curve to the left in the presence of the mentioned carotenoids, which is due to the reduction in the interaction of H1 with DNA. These observations led to the suggesting a mechanism in which the H1 depletion may promote transcription.