Conformational changes associated with template commitment in ATP-dependent chromatin remodeling by ISW2.

Area of Science:

• Molecular Biology
• Chromatin Biology
• Biochemistry

Background:

• ATP-dependent chromatin remodelers play crucial roles in DNA-templated processes.
• The ISWI-type ISW2 complex is essential for regulating nucleosome positioning.
• Understanding the dynamic interplay between remodelers and nucleosomes is key to deciphering gene regulation.

Purpose of the Study:

• To elucidate the distinct conformational changes of the ISW2-nucleosome complex during ATP hydrolysis.
• To characterize the role of ATP binding and hydrolysis in ISW2-nucleosome interactions.
• To investigate the contribution of the Dpb4 subunit to ISW2-mediated chromatin remodeling.

Main Methods:

• Biochemical assays to study ATP-dependent chromatin remodeling.
• Analysis of ISW2 complex formation and stability with nucleosomes.
• Investigating conformational changes using techniques sensitive to protein-DNA interactions.

Main Results:

• ISW2 binding to nucleosomes is enhanced by ATP binding, with initial contacts at extranucleosomal DNA and the dyad axis.
• ATP hydrolysis induces a second conformational change, expanding ISW2's interaction to a full nucleosomal gyre.
• The Dpb4 subunit associates with DNA, potentially disrupting histone-DNA interactions independently of ATPase domain movement.

Conclusions:

• ISW2 utilizes distinct conformational states driven by ATP binding and hydrolysis for stable nucleosome engagement.
• Expanded DNA contacts and Dpb4 association are critical for ISW2's processive nucleosome sliding activity.
• These findings provide mechanistic insights into ATP-dependent chromatin remodeling by ISWI-type complexes.