Cryo-EM reveals open and closed Asgard chromatin assemblies
Harsh M Ranawat1, Marc K Cajili2, Natalia Lopez-Barbosa3
1Molecular Systems Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany; Collaboration for joint PhD degree between EMBL and Heidelberg University, Faculty of Biosciences, 69120 Heidelberg, Germany.
Molecular Cell
|October 29, 2025
Summary
This study reveals the first structures of Asgard chromatin, showing conserved closed and novel open hypernucleosomes. These findings offer insights into chromatin evolution and potential regulatory roles of ions.
Area of Science:
- Molecular Biology
- Evolutionary Biology
- Structural Biology
Background:
- Asgard archaea are the closest archaeal relatives to eukaryotes.
- Understanding Asgard chromatin organization is crucial for tracing eukaryotic chromatin evolution.
- Previous knowledge of Asgard chromatin structure was limited.
Purpose of the Study:
- To determine the high-resolution structures of Asgard chromatin assemblies.
- To elucidate the chromatin organization in Asgard archaea.
- To understand the evolutionary implications of Asgard chromatin structure.
Main Methods:
- High-resolution cryo-electron microscopy (cryo-EM).
- Structural analysis of Hodarchaeal histone HHoB assemblies.
Main Results:
- First structures of Asgard chromatin assemblies reveal compact 'closed' and extended 'open' hypernucleosomes.
- The 'closed' conformation is conserved in archaea; the 'open' conformation resembles eukaryotic H3-H4 octasomes.
- Magnesium ions (Mg²⁺) were shown to influence Asgard chromatin conformation, suggesting a regulatory role.
Conclusions:
- Provides the first structure-based model of Asgard chromatin organization.
- Highlights conserved and novel aspects of chromatin architecture across archaeal and eukaryotic lineages.
- Expands understanding of chromatin evolution and potential ion-mediated regulation in Asgard archaea.
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