A centromere is a specific area in DNA that acts as the control hub for cell division and remains unchanged from one generation of cells to the next. It is distinguished by a unique protein known as centromeric protein A (CENP-A), which identifies the centromere and helps recruit other essential components required for cell division.
A centromere is a specific area in DNA that serves as the control hub for cell division and stays consistent across generations of cells. It is marked by a unique protein called centromeric protein A (CENP-A), which identifies the centromere and facilitates the recruitment of other necessary components for cell division.
“One of the key questions regarding life replication is: how does this structure (the CENP-A marker) accurately restore itself during each cell cycle?,” explains Prof. Dr. Andrea Musacchio from the Max Planck Institute of Molecular Physiology in Dortmund. Musacchio and his team have successfully clarified the molecular mechanism that governs the replenishment of the centromere with CENP-A. They employed various biochemical techniques to investigate how a protein known as Polo-like kinase 1 (PLK1) regulates the assembly of the components responsible for reloading CENP-A.
A series of events
“We have filled a knowledge gap that has existed for a decade,” states Duccio Conti, a postdoc in the Musacchio group and lead author of the publication. During normal DNA replication, each new chromosome initially receives half of the CENP-A proteins at each centromere, which are replenished shortly after division; however, this process is unregulated in cancer cells. Back in 2014, another research team discovered that while an enzyme called CDK1 inhibits the loading of CENP-A for most of the cell cycle, at a specific time during the cycle, PLK1 promotes its refilling. Still, the exact molecular mechanisms of PLK1 remained unclear.
PLK1 plays a role in numerous cellular processes, making the typical approach of completely inhibiting it problematic, as this would disrupt its overall function. “The main challenge was to isolate only PLK1’s specific function related to CENP-A reloading,” mentions Conti. The MPI scientists built on previous research by reconstituting PLK1 and the entire refilling machinery in a test tube, introducing mutations in certain protein areas to determine their involvement in the process. They later verified their findings through cell biology experiments.
It turns out that “PLK1 binds to one component of the refilling complex (which consists of four proteins), causing the arm of one protein to open up and allow the final element of the machinery, the chaperon protein HJURP, to bind. HJURP helps keep CENP-A soluble and stable in the cytoplasm,” Conti explains. PLK1 initiates a cascade of events by triggering a series of chemical (phosphorylation) and conformational changes in neighboring proteins within the machinery. “This discovery,” adds Conti, “opens up new avenues for inquiries into PLK1 and its role in managing the insertion of new CENP-A proteins into the centromere.”
