Abstract
Kinetochores are macromolecular machines that drive eukaryotic chromosome segregation by interacting with centromeric DNA and spindle microtubules. While most eukaryotes possess conventional kinetochore proteins, evolutionarily distant kinetoplastid species have unconventional kinetochore proteins, composed of at least 19 proteins (KKT1–19). Polo-like kinase (PLK) is not a structural kinetochore component in either system. Here, we report the identification of an additional kinetochore protein, KKT20, in Trypanosoma brucei. KKT20 has sequence similarity with KKT2 and KKT3 in the Cys-rich region, and all three proteins have weak but significant similarity to the polo box domain (PBD) of PLK. These divergent PBDs of KKT2 and KKT20 are sufficient for kinetochore localization in vivo. We propose that the ancestral PLK acquired a Cys-rich region and then underwent gene duplication events to give rise to three structural kinetochore proteins in kinetoplastids.
Highlights
Eukaryotic chromosome segregation is directed by the kinetochore, the macromolecular protein complex that assembles onto centromeric DNA and captures spindle microtubules during mitosis and meiosis [1,2]
Unlike KKT4, which localized at the kinetochore throughout the cell cycle, KKT20 localized from S phase until the end of anaphase
Together with our previous result that KKT20 and APC/C subunits were detected only in the KKT4 sample, it is likely that KKT20 and KKT4 are in close proximity at the kinetochore
Summary
Eukaryotic chromosome segregation is directed by the kinetochore, the macromolecular protein complex that assembles onto centromeric DNA and captures spindle microtubules during mitosis and meiosis [1,2]. It is thought that most eukaryotes use these proteins to build kinetochores because of their conservation in diverse eukaryotes [4,5,6,7] None of these conventional kinetochore components has been found in kinetoplastids, a group of evolutionarily distant eukaryotes that include medically important pathogens such as Trypanosoma brucei and Leishmania [8]. These organisms instead have unconventional kinetochores, composed of at least 19 proteins named KKT1–19 (kinetoplastid kinetochore protein) [7].
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