The ATP-dependent Chromatin Remodeling Enzymes CHD6, CHD7, and CHD8 Exhibit Distinct Nucleosome Binding and Remodeling Activities [Enzymology]

Proper chromatin regulation is central to genome function and maintenance. The group III CHD family of ATP-dependent chromatin remodeling enzymes--comprising CHD6, CHD7, CHD8, and CHD9--has well-documented roles in transcription regulation impacting both organism development and disease etiology. These four enzymes are similar in their constituent domains, yet these enzymes fill surprisingly non-redundant roles in the cell, with deficiencies in individual enzymes leading to dissimilar disease states such as CHARGE syndrome or autism spectrum disorders. The mechanisms explaining their divergent, non-overlapping functions are unclear. In this study, we performed an in-depth biochemical analysis of purified CHD6, CHD7, and CHD8, and discovered distinct differences in chromatin remodeling specificities and activities among them. We report that CHD6 and CHD7 both bind with high affinity to short linker DNA, while CHD8 requires longer DNA for binding. As a result, CHD8 slides nucleosomes into positions with more flanking linker DNA than does CHD7. Moreover, we found that while CHD7 and CHD8 slide nucleosomes, CHD6 disrupts nucleosomes in a distinct non-sliding manner. The different activities of these enzymes likely lead to differences in chromatin structure, and thereby transcriptional control, at the enhancer and promoter loci where these enzymes bind. Overall, our work provides a mechanistic basis for both the non-redundant roles, and the diverse mutant disease states, of these enzymes in vivo.

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