Fig 1.
Comparison of the main OM protein translocases between S. cerevisiae (TOM) and Trypanosoma brucei (ATOM).
Tom40/ATOM40 and Tom22/ATOM14 are orthologues and are indicated in orange. Other subunits are shown in light gray. The protein import receptor pairs in yeast (Tom20/Tom70) and trypanosomes (ATOM46/ATOM69) are indicated in bold. They are not evolutionarily related but share the same function. The domain structures of the yeast and the trypanosomal receptor pairs are indicated at the bottom. The depiction of the ATOM complex is schematic; its exact architecture remains to be elucidated. ATOM, atypical translocase of the outer membrane; Hsp20, heat shock protein 20; OM, outer membrane; Tom, translocase of the outer membrance; TPR, tetratricopeptide repeat.
Fig 2.
Comparison between the MIM complex of S. cerevisiae and pATOM36 of T. brucei.
The two complexes that are required for the biogenesis of a subset of OM proteins including subunits of the TOM and ATOM complexes, respectively. The MIM complex consists of Mim1 and Mim2, neither of which shows sequence similarity with pATOM36. Although pATOM36 is an integral membrane protein, its two predicted transmembrane domains have not yet been confirmed experimentally. pATOM36 is dually localized all over the OM and in the TAC (box with dashed lines) that links the mitochondrial DNA with the basal body of the flagellum. Therefore, pATOM36 has an essential function in OM protein biogenesis and as an essential component of the TAC in the segregation of the replicated single unit kDNA of T. brucei. kDNA, kinetoplast DNA; MIM, mitochondrial import machinery; OM, outer membrane; pATOM36, peripheral ATOM of 36 kDa; TAC, tripartite attachment complex.
Fig 3.
Comparison of the inner membrane protein translocases TIM23 and TIM22 of S. cerevisiae with the single T. brucei TIM complex.
Tim22 and TbTim17 are orthologues and are indicated in orange. Other subunits are shown in light grey. The peripherally associated small TIM and the PAM complexes are indicated in dark grey. The composition of the trypanosomal PAM is unknown at present. The two inactive rhomboid-like proteases, TimRhomI and TimRhomII, were specific for the presequence translocase. The depiction of the trypanosomal TIM complex is schematic; its exact architecture remains to be elucidated. ACAD, acyl-CoA dehydrogenase; IM, inner membrane; PAM, presequence-associated motor; Sdh, succinate dehydrogenase; TIM, translocase of the IM.