A human parasite with a streamlined mitochondrion

Mitochondria, as they are defined in textbooks, are essential for eukaryotic cells–including our own–because they make large amounts of energy as they use oxygen. However, some eukaryotic cells, including important parasites of humans–such as Entamoeba histolytica, the causal agent of amoebic dysentery–live in environments that are too oxygen poor to support this process. Nevertheless, Entamoeba still contains a somewhat mysterious organelle, called a mitosome, that is evolutionarily derived from mitochondria. As reported by researchers this week, the mitosome can represent a surprisingly pared-down version of the much more sophisticated mitochondrion.

In their new work on the mitosome, a team led by Edmund Kunji at the MRC Dunn Unit, Jorge Tovar at the Royal Holloway University, and Martin Embley at the University of Newcastle upon Tyne provide intriguing clues to the function of this enigmatic organelle. They show that the mitosome contains a single type of a protein, called a mitochondrial carrier, that in human mitochondria exists in many different specialized versions. In humans, these diverse carriers are needed to import and export the varied chemicals required, or produced, by our complex mitochondria. The presence of a single carrier in the Entamoeba mitosome means that it must be able to do far fewer jobs than our own mitochondria.

Further experiments performed by the team reveal that the Entamoeba carrier can only transport ADP and ATP, suggesting that it could fuel energy-requiring reactions within the mitosome but might not perform other functions. The work suggests that the Entamoeba mitosome may represent the simplest mitochondrion yet described, and thus it provides a model system for probing which mitochondrial functions are truly essential for eukaryotic cells.