Regulation of CtISWI activity by AutoN and HSS domain

Abstract Chromatin remodeler imitation switch (ISWI) plays an important role in regulating chromatin structure through sliding and spacing nucleosomes. Despite the enormous progress in regulatory elements and mechanisms of the activity of ISWI in recent years, there are still some unclear structures and mechanisms in different species. Here, we studied the ATPase activity and nucleosome binding affinity of Chaetomium thermophilum ISWI (hereafter referred to as Ct ISWI WT ) and several mutants, further proving the importance of these mutated residues in the inhibition of AutoN. We also analyzed the effects of dsDNA and ssDNA on ATPase activity of Ct ISWI, suggesting the potential interaction between HSS and ATPase domain. Notably, we provided a predicted structural model based on the sequence of Ct ISWI WT , proposing a two-step activating mechanism of conformation change and activity regulation. Taken together, our findings elucidate a different model of ISWI self-maintenance and action, providing a new mechanism of regulation supporting chromatin remodeling. Highlights Structural modeling of ISWI: a chromatin remodeler that couples to ATP hydrolysis to slide and space composition of nucleosome. The ATPase activity of ISWI can be stimulated by exogenous DNA, with opposite promoting effects by dsDNA and ssDNA. The mechanism by which ISWI is activated upon binding with nucleosome has been the subject of debate, and a more comprehensive mechanism for regulation of ISWI activity. Significance In the past decades, a variety of regulatory mechanisms of the activity of chromatin remodeling factor ISWI have been proposed. Based on the hypothesis of nucleosome complex structure analysis, these studies attempted to explore the mechanism of chromatin remodeling, a gene expression regulation activity. However, previous studies have basically focused on the binding and regulation mechanism of ISWI ATPase domain and nucleosomes, without mentioning the activity mode of full-length ISWI. Therefore, our study mainly focuses on the nearly full-length ISWI containing HSS domain, exploring the mechanism of the active state transition of ISWI in remodeling activities from this perspective. It enriches and supplements the research on chromatin remodeling, an important physiological activity.