 |
| Prof. Dr. Axel Imhof (left) and Prof. Dr. Christoph Kurat at the LMU Biomedical Center. Photo Credit: © LMU / Jan Greune |
Scientific Frontline: Extended "At a Glance" Summary: Chromatin Reorganization and DNA Replication
The Core Concept: Before a cell can divide, its genetic material—tightly packed into a DNA-protein complex known as chromatin—must be temporarily reorganized. This structural modification exposes specific starting points along the DNA, ensuring the cellular machinery can precisely duplicate the genetic information.
Key Distinction/Mechanism: The precise packaging of DNA is temporally coordinated by the enzyme DDK (Dbf4-Dependent Kinase). DDK phosphorylates the chromatin remodeler INO80, acting as a molecular switch that alters INO80's internal structure and boosts its activity. This modification makes INO80 "replication competent," allowing it to precisely position nucleosomes at the replication origins.
Major Frameworks/Components:
- Chromatin and Nucleosomes: The foundational architecture of genetic material, consisting of DNA wrapped around a core of histone proteins.
- Origin Recognition Complex (ORC): A critical regulator that coordinates molecular assistants to achieve the correct DNA structure at replication starting points.
- INO80: A specific chromatin remodeler responsible for organizing nucleosome arrays to expose DNA for copying.
- DDK (Dbf4-Dependent Kinase): An enzyme that chemically modifies (phosphorylates) INO80 to synchronize chromatin organization with the cell cycle.
Branch of Science: Molecular Biology, Biochemistry, and Cell Biology.
Future Application: Advanced understanding of these regulatory mechanisms offers potential therapeutic pathways for diseases characterized by unregulated cell division, such as cancer. By targeting the phosphorylation process or the INO80 remodeler, researchers could theoretically induce or inhibit replication stress in malignant cells.
Why It Matters: This research fundamentally shifts the understanding of nucleosomes, proving they are not merely structural obstacles to DNA replication but decisive regulatory elements. It highlights that cell cycle kinases actively prepare the chromatin landscape in addition to triggering the central replication machinery, ensuring genomic stability during cell division.
Before a cell can divide, it has to precisely duplicate its entire genetic information. However, the DNA in the cell exists as part of a DNA-protein complex known as chromatin. For this purpose, the DNA is wrapped around a core of histone proteins and tightly packed into so-called nucleosomes. So that the genetic material can be reliably copied, the chromatin must be temporarily reorganized in certain places and adopt a very specific architecture. A team led by molecular biologists Professor Axel Imhof and Professor Christoph Kurat at the Biomedical Center (BMC) has now deciphered how the precise packaging of DNA is controlled at the beginning of cell division.
In previous studies, Kurat and his team had already demonstrated that the so-called origin recognition complex (ORC) plays a key role as regulator of the chromatin structure. This complex coordinates various molecular assistants, including the chromatin remodeler INO80.
These molecules ensure that the correct structure is achieved at the starting points of DNA replication – the so-called origins: It is precisely here that a piece of DNA must be exposed and flanked by regularly spaced nucleosome arrays. This particular arrangement is essential, as cellular replication machinery can only begin copying the genetic material when the DNA is correctly organized here.
Phosphorylation functions as molecular switch
In their latest study, the researchers investigated the critical question as to how this chromatin organization is temporally coordinated with the cell cycle. They focused particularly on the enzyme DDK (Dbf4-Dependent Kinase), which was chiefly known for its direct activation of the central replication machinery. By means of a comprehensive proteomic analysis, the researchers demonstrated that the chromatin remodeler INO80 is also a key target of DDK. The enzyme is a so-called kinase, meaning it chemically modifies its target molecules by transferring phosphate groups to them. This phosphorylation functions like a molecular switch, as it alters the internal structure of INO80 and increases its activity.
Without this modification, INO80 cannot position the nucleosomes precisely enough at the replication origins. And so, it is ensured that INO80 becomes “replication competent” at exactly the right moment. Cells that lack this phosphorylation exhibit clear delays in starting replication and respond extremely sensitively to replication stress.
“Our findings show that cell cycle kinases, beyond the tasks they perform for the central replication machinery, also prepare the ‘landscape’ in which these machines operate,” explain Imhof and Kurat. “This makes it increasingly clear that nucleosomes are not just obstacles to replication but also play a decisive role in controlling important processes.”
Published in journal: Nature Communications
Title: Dbf4-dependent kinase finetunes Ino80 function at chromosome replication origins
Authors: Priyanka Bansal, Shibojyoti Lahiri, Chandni Natalia Kumar, Jessica Furtmeier, Lorenz Spechtenhauser, Lorenzo Galanti, Juan de Dios Barba Tena, Erika Chacin, Garp Linder, María Ángeles Ortíz-Bazán, Marisa Müller, Petra Vizjak, Tobias Straub, Felix Mueller-Planitz, Johannes Stigler, Andrés Aguilera, Belen Gómez-González, Boris Pfander, Philipp Korber, Axel Imhof, and Christoph F. Kurat
Source/Credit: Ludwig-Maximilians-Universität München
Reference Number: mbio033126_01