|Sorting switch of mitochondrial presequence translocase involves coupling of motor module to respiratory chain|
Wiedemann N, van der Laan M, Hutu DP, Rehling P, Pfanner N
Journal of Cell Biology (2007)
Category: mitochondria-biogenesis, respiration ¤ Added: Dec 18, 2007 ¤ Rating: ◊◊
The mitochondrial presequence translocase transports preproteins to either matrix or inner membrane. Two different translocase forms have been identiï¬ ed: the matrix transport form, which binds the heatshock protein 70 (Hsp70) motor, and the inner membraneâ sorting form, which lacks the motor but contains translocase of inner mitochondrial membrane 21 (Tim21). The sorting form interacts with the respiratory chain in a Tim21- dependent manner. It is unknown whether the respiratory chainâbound translocase transports preproteins and how the switch between sorting form and motor form occurs. We report that the respiratory chainâbound translocase contains preproteins in transit and, surprisingly, not only sorted but also matrix-targeted preproteins. Presequence translocase-associated motor (Pam) 16 and 18, two regulatory components of the six-subunit motor, interact with the respiratory chain independently of Tim21. Thus, the respiratory chainâbound presequence translocase is not only active in preprotein sorting to the inner membrane but also in an early stage of matrix translocation. The motor does not assemble en bloc with the translocase but apparently in a step-wise manner with the Pam16/18 module before the Hsp70 core.