ISWI is an Intrinsically Dynamic Nucleosome Remodeler That Induces Large-scale Histone Dynamics

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• The ISWI chromatin remodeler is essential for dynamic chromatin regulation.
• Nucleosome remodeling by ISWI involves DNA translocation without nucleosome disassembly.
• The role of histone conformational changes and ISWI regulatory domains in remodeling is not fully understood.

Purpose of the Study:

• To investigate the conformational dynamics of fruit fly ISWI and its nucleosome complex.
• To elucidate the role of histone plasticity in ISWI-mediated nucleosome remodeling.

Main Methods:

• Solution NMR spectroscopy was employed to study ISWI and nucleosome-ISWI complexes.
• Methyl-TROSY (Methyl-cross-polarization with Transverse Relaxation-Optimized Spectroscopy) was used to analyze dynamics.
• Conformational changes in histones upon ISWI binding were compared.

Main Results:

• The ISWI NTR domain has a dynamic DNA-binding loop; the NegC domain interacts with ATPase lobe 2 in the free enzyme.
• ISWI exhibits significant μs-ms motions in its ATPase lobes and NegC domain, suggesting intrinsic conformational encoding.
• ISWI binding induces substantial conformational changes in the histone octamer, impacting histone-DNA and histone-histone contacts.

Conclusions:

• ISWI's conformational dynamics are intrinsically encoded, facilitating the catalytic cycle.
• Histone octamer plasticity is crucial for DNA translocation during remodeling.
• The histone octamer acts as an allosteric unit in ISWI-mediated chromatin remodeling.