Biology subjects

von Känel, C.

Publications and source records attributed to von Känel, C..

3 recordsLinked to original sources

bioRxiv2025

TbTim20 facilitates protein import at a low membrane potential in trypanosomes lacking the mitochondrial genome

Protein import across the mitochondrial inner membrane typically depends on two protein translocases of the inner membrane (TIM) complexes and the membrane potential. The protozoan parasite Trypanosoma brucei, however, has a single, divergent TIM complex. Unlike other trypanosomal TIM subunits, TbTim20 is neither essential for normal growth of insect nor bloodstream forms of T. brucei, leaving its role uncertain. Specific mutations in the {gamma}-subunit of the F1FO-ATPase, such as {gamma}L262P, permit bloodstream form trypanosomes to grow without mitochondrial DNA (kinetoplast or kDNA). Here we show that RNAi-mediated depletion of TbTim20 inhibits growth of this cell line, but only if it lacks the kDNA. Titration of mitochondrial uncouplers and direct membrane potential measurements reveal that TbTim20 becomes more critical as the membrane potential decreases across all tested cell lines. Proteomic analysis of the uninduced and induced {gamma}L262P TbTim20-RNAi cell line, which lacks kDNA and exhibits the lowest membrane potential, shows depletion of a subset of imported proteins. This subset includes ATPase subunits, suggesting a mechanism by which TbTim20-silenced cell lines become more sensitive to uncouplers. Thus, we propose that TbTim20 supports import of a subset of proteins whose import is hypersensitive to a low membrane potential.

biochemistry↗

bioRxiv2023

Evolutionary repurposing of trypanosomal Pam18 and Pam16 reveals a new regulatory circuit for mitochondrial genome replication

Protein import and genome replication are essential processes for mitochondrial biogenesis and propagation. The J-domain proteins Pam16 and Pam18 regulate the presequence translocase of the mitochondrial inner membrane. In the protozoan Trypanosoma brucei, their counterparts are TbPam16 and TbPam18, which are essential for the procyclic form of the parasite, though not involved in mitochondrial protein import. Here, we show that during evolution, the two proteins have been repurposed to regulate the replication of maxicircles within the intricate kDNA network, the most complex mitochondrial genome known. TbPam18 and TbPam16 have inactive J-domains suggesting a function independent of heat shock proteins. However, their single transmembrane domain is essential for function. Pulldown of TbPam16 identifies a putative client protein, termed MaRF11, the depletion of which causes the selective loss of maxicircles, akin to the effects observed for TbPam18 and TbPam16. Moreover depletion of the mitochondrial proteasome results in increased levels of MaRF11. Thus, we propose a model for a membrane-bound regulatory circuit that controls maxicircle replication in response to an unknown nuclear signal. This model posits that MaRF11 directly mediates maxicircle replication, that its level is controlled by proteasomal digestion, and that it is protected from degradation by binding to the TbPam18/TbPam16 dimer.

biochemistry↗

bioRxiv2022

The Mba1 homologue of Trypanosoma brucei is involved in the biogenesis of oxidative phosphorylation complexes

Consistent with other eukaryotes, the Trypanosoma brucei mitochondrial genome encodes mainly hydrophobic core subunits of the oxidative phosphorylation system. These proteins must be co-translationally inserted into the inner mitochondrial membrane and are synthesized by the highly divergent trypanosomal mitoribosomes, which have a much higher protein to RNA ratio than any other ribosome. Here, we show that the trypanosomal ortholog of the mitoribosome receptor Mba1 (TbMba1) is essential for normal growth of procyclic trypanosomes but redundant in the bloodstream form, which lacks an oxidative phosphorylation system. Proteomic analyses of TbMba1-depleted mitochondria from procyclic cells revealed reduced levels of many components of the oxidative phosphorylation system, most of which belong to the cytochrome c oxidase (Cox) complex, three subunits of which are mitochondrially encoded. However, the integrity of the mitoribosome and its interaction with the inner membrane were not affected. Pulldown experiments showed that TbMba1 forms a dynamic interaction network that includes the trypanosomal Mdm38/Letm1 ortholog and a trypanosome-specific factor that stabilizes the CoxI and CoxII mRNAs. In summary, our study suggests that the function of Mba1 in the biogenesis of membrane subunits of OXPHOS complexes is conserved among yeast, mammalian, and trypanosomes, which belong to two eukaryotic supergroups.

biochemistry↗