A protein complex's function in chromosome segregation is revealed by studying its structure

A protein complex has been revealed to play a foundational role in the machine that directs chromosome segregation during cell division. The study is published online by Whitehead Institute researchers this week in the journal Molecular Cell.

The kinetochore serves as an attachment point for microtubules in the process of chromosome segregation. In human cells, a protein complex, Constitutive Centromere-Associated Network (CCAN), critical for recruiting the kinetochore to a specific point on each chromosome. If there is no 16-subunit CCAN, the link between kinetochore and chromosome will fail so will the chromosome segregation and cell division.

The connection of DNA and the segregation machinery is formed by the CCAN. Hence learning about the organization of CCAN can help researchers to know how it targets specifically to the right part of the chromosome and the properties that underlie its role in kinetochore stability.

The researchers then used the CRISPR-Cas9 genome editing system to knock out each subunit and introduce tags that cause the cell to chew up a given subunit through addition of a drug. Though there are research relied on RNAi and other methods to knock down the proteins' expression, there is no achievement of the clean removal of the individual CCAN subcomplexes that is necessary for deciphering their position and function. After studying the sixteen CCAN proteins, McKinley finally could refine the relationships seen in cells and understand how each individual subcomplex touches the others.

It was a surprising finding that each subcomplex needs to be connected in a mesh by touching many other subcomplexes to be functional. The property is important to for kinetochore assembly to build a stable structure. This model helps to explain that the connections between the subcomplexes assist he CCAN tolerate the changes it is exposed to throughout the cell cycle. Besides, these proteins are crucial in resisting the forces that pull on the kinetochore in the process of chromosome segregation. The interconnected framework of interactions is better able to withstand force than is a linear bridge.

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