Discussion

The kinetoplast (k), the uniquely packaged mitochondrial DNA of trypanosomatid protists, is formed by a concatenated network of minicircles and maxicircles that divide and segregate once each cell cycle.  Although many proteins involved in kDNA replication and segregation are known, several key steps in this complex mechanism remain undescribed at the molecular level. Here we characterize an M17 family leucyl aminopeptidase metalloprotease, termed TbLAP1, which specifically localizes to the kDNA disk. Significantly, TbLAP1 is the first known protein of the nabelschnur or umbilicus, a prominent structure which in the human parasite Trypanosoma brucei connects the daughter kDNA networks prior to their segregation; so far the nabelschnur has been characterized solely by morphology. We show that TbLAP1 is required for correct segregation of kDNA and the tripartite attachment complex, and its overexpression leads to loss of kDNA, decreased mitochondrial membrane potential and cell proliferation.  We propose that TbLAP1 is required for efficient kDNA division and specifically participates in the separation of daughter kDNA networks.