The preprotein translocase of the mitochondrial inner membrane: function and evolution

The direct route: a simplified pathway for protein import into the mitochondrion of trypanosomes

“…A single inner membrane translocase The Tim17-Tim22-Tim23 family of proteins (PFAM: PF02466) [22] are a set of highly-conserved proteins found in animals, plants, fungi and protists that range from Plasmodium to Trichomonas [2,23,24]. In all cases, the protein has four predicted transmembrane domains with specific amino acid signature motifs [23].…”

“…In all cases, the protein has four predicted transmembrane domains with specific amino acid signature motifs [23]. In yeast and in humans, two members of the family (Tim23 and Tim17) combine to form the translocation channel of the TIM23 complex to which the presequence-associated motor complex docks (Figure 2).…”

“…We suggest that a primitive protein, TimX, fulfilled this role and thereby serves as the founding member of the Tim23-Tim17-Tim22 protein family. It is possible that TimX was derived from a bacterial LivH-type amino acid translocase [23], although this remains to be established.…”

“…In an initial condition, 'import' of the ADP/ATP carrier (AAC) protein into the inner membrane of a bacterial endosymbiont was inefficient and perhaps mediated by pre-existing bacterial proteins. The inner membrane component assisting assembly of the AAC is referred to as TimX, which might be related to LivH-type amino acid transporters [23]. With effective delivery of ATP to the cytosol being a driving force, changes in TimX to make it a better translocase would be highly selectable.…”

Dual Location of the Mitochondrial Preprotein Transporters B14.7 and Tim23-2 in Complex I and the TIM17:23 Complex in Arabidopsis Links Mitochondrial Activity and Biogenesis

“…Arabidopsis thaliana contains 17 genes encoding proteins that belong to the Preprotein and Amino acid Transport family (PRAT) (Rassow et al, 1999), of which 10 proteins are located in mitochondria, six are located in plastids, and one protein is dual targeted to mitochondria and plastids . Of the 10 mitochondrial PRAT proteins, phylogenetic analysis suggested that three genes encode Tim17, three genes encode Tim23, two identical genes encode Tim22, and three genes encode proteins of unknown function .…”