Kinesiin5

Kinesiin5 is a member of the kinesin superfamily, a group of motor proteins that play a critical role in intracellular transport within eukaryotic cells. Kinesins are ATP-dependent proteins that move along microtubules, facilitating the movement of organelles, vesicles, and chromosomes. Kinesiin5, also known as Eg5 (for eggless, due to its discovery in *Drosophila*), is a dimeric motor protein composed of two heavy chains and two light chains.

This protein is particularly well-studied for its role in mitosis, the process by which cells divide. During mitosis, Eg5 contributes to the separation of sister chromatids by sliding antiparallel microtubules apart, a process essential for the formation of the mitotic spindle. The mitotic spindle is a structure that ensures chromosomes are evenly distributed between daughter cells. Eg5’s activity is tightly regulated, as improper spindle formation can lead to chromosomal missegregation, a hallmark of cancer cells.

Eg5 has been identified across various species, including humans, where it is encoded by the *KIF11* gene. Its inhibition has become a target for cancer therapy, as many tumor cells rely on Eg5 for proper mitotic spindle function. Small-molecule inhibitors of Eg5, such as monastrol, disrupt spindle formation and induce mitotic arrest, leading to cell death in rapidly dividing cancer cells. This mechanism has been explored in preclinical and clinical settings for the treatment of certain cancers, including breast, lung, and ovarian cancers.

Structurally, Eg5 consists of a motor domain at its N-terminus, which binds microtubules and hydrolyzes ATP, and a coiled-coil stalk region that mediates dimerization. The C-terminal region is less well-defined but may interact with regulatory proteins. Mutations in *KIF11* have been linked to rare genetic disorders, such as congenital malformations, though Eg5’s primary role remains tied to cell division and spindle dynamics.