Research Unit for Tropical Diseases, de Duve Institute, Laboratory of Biochemistry, Université catholique de Louvain, Brussels, Belgium.
Biochem Biophys Res Commun. 2012 Aug 10;424(4):781-5. doi: 10.1016/j.bbrc.2012.07.035. Epub 2012 Jul 16.
Trypanosoma brucei contains peroxisome-like organelles designated glycosomes because they sequester the major part of the glycolytic pathway. Import of proteins into the peroxisomal matrix involves a protein complex associated with the peroxisomal membrane of which PEX13 is a component. Two very different PEX13 isoforms have recently been identified in T. brucei. A striking feature of one of the isoforms, TbPEX13.1, is the presence of a C-terminal type 1 peroxisomal-targeting signal (PTS1), the tripeptide TKL, conserved in its orthologues in all members of the Trypanosomatidae family so far studied, but absent from TbPEX13.2 and the PEX13s in all other organisms. Despite their differences, both TbPEX13s function as part of a docking complex for cytosolic receptors with bound matrix proteins to be imported. We further characterized TbPEX13.1's function in glycosomal matrix-protein import. It provides a frame to anchor another docking complex component, PEX14, to the glycosomal membrane or information to correctly position it within the membrane. To investigate the possible function of the C-terminal TKL, we determined the topology of the C-terminal half of TbPEX13.1 in the membrane and show that its SH3 domain, located immediately adjacent to the PTS1, is at the cytosolic face.
布氏锥虫含有过氧化物酶体样细胞器，被称为糖酵解体，因为它们隔离了糖酵解途径的主要部分。蛋白质向过氧化物酶体基质中的输入涉及与过氧化物酶体膜相关的蛋白质复合物，其中 PEX13 是一个组成部分。最近在 T. brucei 中鉴定出两种非常不同的 PEX13 同工型。一种同工型 TbPEX13.1 的一个显著特征是存在 C 末端的 1 型过氧化物酶体靶向信号 (PTS1)，三肽 TKL，在迄今为止研究的所有锥虫科成员的同源物中保守，但在 TbPEX13.2 和所有其他生物的 PEX13 中缺失。尽管存在差异，但两种 TbPEX13 都作为与结合基质蛋白的细胞质受体的对接复合物的一部分发挥作用，以进行导入。我们进一步表征了 TbPEX13.1 在糖酵解体基质蛋白导入中的功能。它提供了一个框架，将另一个对接复合物成分 PEX14 锚定在糖酵解体膜上，或提供正确定位在膜内的信息。为了研究 C 末端 TKL 的可能功能，我们确定了 TbPEX13.1 的 C 末端半部分在膜中的拓扑结构，并表明其位于 PTS1 旁边的 SH3 结构域位于细胞质侧。
