Conserved regions of budding yeast Tim22 have a role in structural organization of the carrier translocase.

Mitochondrial biogenesis requires efficient sorting of various proteins into different mitochondrial sub-compartments, mediated by dedicated protein machinery present in the outer and inner membrane. Among them, the TIM22 complex enables the integration of complex membrane proteins with internal targeting signals into the inner membrane. Although the Tim22 protein forms the core of the complex, the dynamic recruitment of subunits to the channel is still enigmatic. In this study, we highlight that the intermembrane space (IMS) and transmembrane 4 (TM4) regions of Tim22 are critically required for interactions with the membrane-embedded subunits, including Tim54, Tim18, and Sdh3, and thereby maintain the functional architecture of the TIM22 translocase. Furthermore, we find that the TM1 and TM2 regions of Tim22 are important for association with Tim18, whereas TM3 is exclusively required for the interaction with Sdh3. Moreover, impairment of TIM22 complex assembly influences its translocase activity, the mitochondrial network, and the viability of cells lacking mitochondrial DNA. Overall, our findings provide compelling evidence highlighting the significance of conserved regions of Tim22 that are important for the maintenance of the TIM22 complex and mitochondrial integrity.

Kumar A ，Matta SK ，D'Silva P 《-》

Mitochondrial protein import: Mia40 facilitates Tim22 translocation into the inner membrane of mitochondria.

Wrobel L ，Trojanowska A ，Sztolsztener ME ，Chacinska A ... -  《-》

A MICOS-TIM22 Association Promotes Carrier Import into Human Mitochondria.

Mitochondrial membrane proteins with internal targeting signals are inserted into the inner membrane by the carrier translocase (TIM22 complex). For this, precursors have to be initially directed from the TOM complex in the outer mitochondrial membrane across the intermembrane space toward the TIM22 complex. How these two translocation processes are topologically coordinated is still unresolved. Using proteomic approaches, we find that the human TIM22 complex associates with the mitochondrial contact site and cristae organizing system (MICOS) complex. This association does not appear to be conserved in yeast, whereby the yeast MICOS complex instead interacts with the presequence translocase. Using a yeast mic10Δ strain and a HEK293T MIC10 knockout cell line, we characterize the role of MICOS for protein import into the mitochondrial inner membrane and matrix. We find that a physiological cristae organization promotes efficient import via the presequence pathway in yeast, while in human mitochondria, the MICOS complex is dispensable for protein import along the presequence pathway. However, in human mitochondria, the MICOS complex is required for the efficient import of carrier proteins into the mitochondrial inner membrane. Our analyses suggest that in human mitochondria, positioning of the carrier translocase at the crista junction, and potentially in vicinity to the TOM complex, is required for efficient transport into the inner membrane.

Callegari S ，Müller T ，Schulz C ，Lenz C ，Jans DC ，Wissel M ，Opazo F ，Rizzoli SO ，Jakobs S ，Urlaub H ，Rehling P ，Deckers M ... -  《-》

Dual function of Sdh3 in the respiratory chain and TIM22 protein translocase of the mitochondrial inner membrane.

The mitochondrial inner membrane harbors the complexes of the respiratory chain and translocase complexes for precursor proteins. We have identified a further subunit of the carrier translocase (TIM22 complex) that surprisingly is identical to subunit 3 of respiratory complex II, succinate dehydrogenase (Sdh3). The membrane-integral protein Sdh3 plays specific functions in electron transfer in complex II. We show by genetic and biochemical approaches that Sdh3 also plays specific functions in the TIM22 complex. Sdh3 forms a subcomplex with Tim18 and is involved in biogenesis and assembly of the membrane-integral subunits of the TIM22 complex. We conclude that the assembly of Sdh3 with different partner proteins, Sdh4 and Tim18, recruits it to two different mitochondrial membrane complexes with functions in bioenergetics and protein biogenesis, respectively.

Gebert N ，Gebert M ，Oeljeklaus S ，von der Malsburg K ，Stroud DA ，Kulawiak B ，Wirth C ，Zahedi RP ，Dolezal P ，Wiese S ，Simon O ，Schulze-Specking A ，Truscott KN ，Sickmann A ，Rehling P ，Guiard B ，Hunte C ，Warscheid B ，van der Laan M ，Pfanner N ，Wiedemann N ... -  《-》

Mutations of the mitochondrial carrier translocase channel subunit TIM22 cause early-onset mitochondrial myopathy.

Pacheu-Grau D ，Callegari S ，Emperador S ，Thompson K ，Aich A ，Topol SE ，Spencer EG ，McFarland R ，Ruiz-Pesini E ，Torkamani A ，Taylor RW ，Montoya J ，Rehling P ... -  《-》