The C-terminal tripeptide of glycosomal phosphoglycerate kinase is both necessary and sufficient for import into the glycosomes of Trypanosoma brucei

Glycosomal phosphoglycerate kinase (gPGK) of Trypanosoma brucei differs from the cytoplasmic isozyme (cPGK) in its higher isoelectric point characterized by clusters of positive charges along the polypeptide chain, and a 20 amino acid C-terminal extension ending in serine-serine-leucine (SSL). While a C-terminal SSL tripeptide is apparently not capable of directing luciferase to the peroxisomes in mammalian cells [J. Cell Biol. 108 (1989), 1657-1664], we show here that it is sufficient for the import of luciferase as well as an unrelated protein, β-glucuronidase, into the glycosomes of T. brucei, as determined by immunoelectron microscopy. The analysis of luciferase-gPGK fusion proteins indicates that the only targeting signal for import of gPGK into the glycosome resides in this C-terminal SSL sequence.