An essential dimeric membrane protein of trypanosome glycosomes

Kinetoplastid parasites compartmentalize the first seven enzymes of glycoly sis in a peroxisome-like microbody, the glycosome. Genes encoding the most abundant protein of the glycosomal membrane, GIM5, have been cloned and the protein characterized. Two genes, GIM5A and GIM5B, encode 26 kDa proteins. Although many microbody membrane proteins are conserved in evolution, the only homologues of GIM5 in the available databases are from the closely rel ated kinetoplastids Trypanosoma cruzi and Leishmania. The N- and C-termini are conserved between the two genes, and between species, and are oriented towards the cytosol. They are separated by a short loop that is located bet ween two transmembrane domains and shows almost no sequence conservation. T his suggests that the N- and C-terminal domains are more important for func tion. GIM5 forms dimers in vivo. Overexpression of GIM5B inhibits growth, w hereas depletion of GIM5 to below 10% of wild-type levels is very rapidly l ethal. This novel organellar membrane protein is therefore essential for bl oodstream trypanosome survival.