The New Shape of EC

ABSTRACT The journal Eukaryotic Cell has served the eukaryotic microbiology community since 2002. It will continue to do so as it merges into the new broad-scope open-access journal mSphere in 2016.

N-Terminal Presequence-Independent Import of Phosphofructokinase into Hydrogenosomes of Trichomonas vaginalis

ABSTRACT Mitochondrial evolution entailed the origin of protein import machinery that allows nuclear-encoded proteins to be targeted to the organelle, as well as the origin of cleavable N-terminal targeting sequences (NTS) that allow efficient sorting and import of matrix proteins. In hydrogenosomes and mitosomes, reduced forms of mitochondria with reduced proteomes, NTS-independent targeting of matrix proteins is known. Here, we studied the cellular localization of two glycolytic enzymes in the anaerobic pathogen Trichomonas vaginalis : PP i -dependent phosphofructokinase ( Tv PP i -PFK), which is the main glycolytic PFK activity of the protist, and ATP-dependent PFK ( Tv ATP-PFK), the function of which is less clear. Tv PP i -PFK was detected predominantly in the cytosol, as expected, while all four Tv ATP-PFK paralogues were imported into T. vaginalis hydrogenosomes, although none of them possesses an NTS. The heterologous expression of Tv ATP-PFK in Saccharomyces cerevisiae revealed an intrinsic capability of the protein to be recognized and imported into yeast mitochondria, whereas yeast ATP-PFK resides in the cytosol. Tv ATP-PFK consists of only a catalytic domain, similarly to “short” bacterial enzymes, while Sc ATP-PFK includes an N-terminal extension, a catalytic domain, and a C-terminal regulatory domain. Expression of the catalytic domain of Sc ATP-PFK and short Escherichia coli ATP-PFK in T. vaginalis resulted in their partial delivery to hydrogenosomes. These results indicate that Tv ATP-PFK and the homologous ATP-PFKs possess internal structural targeting information that is recognized by the hydrogenosomal import machinery. From an evolutionary perspective, the predisposition of ancient ATP-PFK to be recognized and imported into hydrogenosomes might be a relict from the early phases of organelle evolution.