The pre-protein translocase of the mitochondrial outer membrane (Tom) allows the import of pre-proteins from the cytoplasm. Tom forms a complex with a number of proteins, including Tim17 [1, 2, 3]. Tim17, Tim22, and Tim23, are the central components of the widely conserved multi-subunit protein translocases, TIM23 and TIM22, which mediate protein transport across and into the inner mitochondrial membrane, respectively [4]. In addition, several Tim17 family proteins occupy the inner and outer membranes of plastids. This family also includes Pmp24 a peroxisomal protein. The involvement of this domain in the targeting of PMP24 remains to be proved. PMP24 was known as Pmp27 [3]. Family members are suggested to be exclusive to eukaryotes, where the distribution in the eukaryotic subgroups of the mitochondrial Tim17, Tim22 and Tim23 proteins, as well as the peroxisomal Tim17 family proteins, suggests that they all likely to be present in the last eukaryotic common ancestor (LECA) [4].

1: The preprotein translocase of the inner mitochondrial membrane: evolutionary conservation of targeting and assembly of Tim17. Bomer U, Rassow J, Zufall N, Pfanner N, Meijer M, Maarse AC; J Mol Biol 1996;262:389-395. PMID:8893850

2: Identification of a 24 kDa intrinsic membrane protein from mammalian peroxisomes. Reguenga C, Oliveira ME, Gouveia AM, Eckerskorn C, Sa-Miranda C, Azevedo JE; Biochim Biophys Acta. 1999;1445:337-341. PMID:10366717

3: Pmp27 promotes peroxisomal proliferation. Marshall PA, Krimkevich YI, Lark RH, Dyer JM, Veenhuis M, Goodman JM; J Cell Biol. 1995;129:345-355. PMID:7721939

4: Evolution of the Tim17 protein family. Zarsky V, Dolezal P; Biol Direct. 2016;11:54. PMID:27760563