Function of N‐terminal import signals in trypanosome microbodies

Abstract

The glycosomes of trypanosomes are related to eukaryotic peroxisomes. For many glycosomal and peroxisomal proteins, a C-terminal SKL-like tripeptide known as PTS-1 serves as the targeting signal. For peroxisomes, a second N-terminal signal (PTS-2) was demonstrated on rat 3-ketoacyl-CoA thiolase. Several glycosomal proteins do not bear a PTS-1. One such protein, fructose bisphosphate aldolase, has a PTS-2 homology at its N-terminus. To find out whether the PTS-2 pathway exists in trypanosomes, we expressed chloramphenicol acetyltransferase fusion proteins bearing N-terminal segments of either rat thiolase or trypanosome aldolase. The mammalian PTS-2 clearly mediated glycosomal import. The aldolase N-terminus mediated import with variable efficiency depending on the length of the appended sequence. These results provide evidence for the existence of the PTS-2 pathway in trypanosomes.

Caenorhabditis elegans has a single pathway to target matrix proteins to peroxisomes

“…We used the presequence of rat 3-ketoacyl-CoA thiolase fused to GFP as a reporter protein for PTS2 import. Rat thiolase PTS2 has previously been shown to import a reporter protein into peroxisomes of plants (Flynn et al, 1998) and trypanosomes (Blattner et al, 1995). In C. elegans, however, a diffuse pattern of staining is seen after expression of PTS2-GFP (Figure 1F).…”

Moonlighting Proteins: The Case of the Hexokinases

“…In Trypanosoma brucei , TbHK1 and TbHK2 are expressed in bloodstream-form and procyclic stage parasites in different developmental stages, and TbHK2 has been localized in the flagelum inside and outside of the glycosomes, specialized structures that contain glycolytic enzymes ( Blattner et al, 1995 ; Michaels et al, 2006 ). The ability of TbHK2 to be on different compartments in the cell might help to have different functions.…”

“…A distinct feature of some hexokinases that might contribute to its moonlighting activity is their subcellular location: some of them, like S. cerevisiae HXK2 ( Fernández-García et al, ) and maize HXK7 and HXK8 ( Aguilera-Alvarado et al, 2019 ) are located at the cytoplasm; others, in glycosomes, like T. brucei HXK2 ( Blattner et al, 1995 ; Michaels et al, 2006 ); many in the mitochondrial outer membrane or MOM, like human HXKII ( Arora and Pedersen, 1988 ; Dubey et al, 2016 ), A. thaliana HXK1 ( Cho et al, 2006a ) and apple HXK1 ( Sun et al, 2018 ); or in the chloroplast, like P. patens HXK1 ( Olsson et al, 2003 ) and Oryza sativa HXK4 ( Cho et al, 2006a ). And even there are HXKs that are translocated from one subcellular compartment to the nucleus, like AtHXK1 ( Cho et al, 2006b ) and ScHXK2 ( Vega et al, 2016 ).…”

Extra-glycosomal localisation of Trypanosoma brucei hexokinase 2

“…The glycosomal localization of the TbHKs has been attributed to the presence of a N-terminal peroxisomal targeting sequence (PTS2), as this sequence has been shown to be responsible for the import of other glycosomally-targeted proteins (Blattner et al, 1995). Here, we report the unexpected life cycle-dependent dual localization of TbHK2.…”