Mitochondrial protein import in trypanosomatids: Variations on a theme or fundamentally different?

Mitochondria perform many important functions. Their origin can be traced back to an endosymbotic event between an archaeal host cell and an α-proteobacteria approximately 2 billion years ago [1]. Subsequently, the endosymbiont was converted into an organelle, which learned to import cytosolic proteins, a feat present-day endosymbiontic bacteria are not capable of. Today, the large majority of mitochondrial proteins are encoded in the nucleus, synthesized in the cytosol, and finally imported across the outer and/or the inner mitochondrial membranes. Protein import was one of the first—if not the first—mitochondria-specific trait to evolve. Because mitochondria are monophyletic, the expectation was that the machineries that mediate mitochondrial protein import would be largely conserved. Work in trypanosomes and other organisms in recent years has shown that this is not the case [2, 3]. It is the aim of this review to summarize where we find major deviations in the trypanosomal mitochondrial protein import machineries when compared to the best-studied system, that of the yeast Saccharomyces cerevisiae.