If I could shrink down into a cell like in “Body Wars” at Disney’s Epcot, the first place I would travel to would be the kinetochore. The kinetochore is made of over 80 proteins which are each regulated to provide a mind-numbing level of complexity to its task of ensuring accurate chromosome segregation during mitosis.
Kinetochores are the structures on chromosomes where spindle microtubules attach during mitosis, and are responsible for generating the signal for accurate chromosome segregation. Because of the dynamic signaling required at the kinetochore, many proteins use phosphorylation to serve as rapid “molecular switches.” Phosphorylation is the addition of a phosphate group onto a protein, which alters the protein’s activity in some way, while dephosphorylation reverses the switch. Aurora B is a protein that phosphorylates many kinetochore proteins during mitosis, and a recent paper looks at how Aurora B is regulated by a protein called Sds22, which modulates a protein responsible for dephosphorylation. Images above show mitotic spindles (green) in control (top) and Sds22-depleted (bottom) human cells. Hec1 is a kinetochore protein (right, red in merged) that is phosphorylated by Aurora B; the phosphorylated form of Hec1 is the center image (blue in merged). Surprisingly, Sds22 depletion caused a decrease in phosphorylation of Hec1, suggesting that Sds22 modulates the phosphorylation activity of Aurora B.
Reference: Markus Posch, Guennadi A. Khoudoli, Sam Swift, Emma M. King, Jennifer G. DeLuca, and Jason R. Swedlow, 2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.200912046. Paper can be found here.
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