Tim23–Tim50 pair coordinates functions of translocators and motor proteins in mitochondrial protein import

Abstract

Mitochondrial protein traffic requires coordinated operation of protein translocator complexes in the mitochondrial membrane. The TIM23 complex translocates and inserts proteins into the mitochondrial inner membrane. Here we analyze the intermembrane space (IMS) domains of Tim23 and Tim50, which are essential subunits of the TIM23 complex, in these functions. We find that interactions of Tim23 and Tim50 in the IMS facilitate transfer of precursor proteins from the TOM40 complex, a general protein translocator in the outer membrane, to the TIM23 complex. Tim23–Tim50 interactions also facilitate a late step of protein translocation across the inner membrane by promoting motor functions of mitochondrial Hsp70 in the matrix. Therefore, the Tim23–Tim50 pair coordinates the actions of the TOM40 and TIM23 complexes together with motor proteins for mitochondrial protein import.

The presequence pathway is involved in protein sorting to the mitochondrial outer membrane

“…We thus analysed mutant mitochondria, which are impaired in subunits of the TIM23 complex [29][30][31][32]. Conditional mutants of the essential subunits Tim23, Tim50 and Tim17 were considerably impaired in the import of Om45 (Fig 3B and C).…”

A novel import route for an N-anchor mitochondrial outer membrane protein aided by the TIM23 complex

“…The TOM40 complex consists of multiple subunits including presequence receptors, Tom20 and Tom22, and a channel-forming protein, Tom40. Tim50 of the TIM23 complex receives a presequence from the Tom40 channel and transfers it to the Tim23 channel, depending on the membrane potential (DΨ) across the IM [4][5][6]. Matrix-targeted proteins subsequently use an import motor mitochondrial Hsp70 (mtHsp70) and its partner proteins for translocation and unfolding, while IM-sorted proteins with a hydrophobic sorting signal downstream of the matrixtargeting signal in the presequence require translocation arrest at the TIM23 channel followed by lateral release into the IM.…”

Mic60/Mitofilin determines MICOS assembly essential for mitochondrial dynamics and mtDNA nucleoid organization

“…1,2 In contrast, the mitochondrial inner membrane consists of two morphologically distinct regions: the inner boundary membrane is in close proximity to the outer membrane and the cristae membranes that are large tubular invaginations. [3][4][5][6][7][8] The mitochondrial inner boundary and cristae membrane are physically separated by cristae junctions, which are narrow tubular or slot-like structure. 4,9 The mitochondrial cristae are arranged in regular arrays and are the main sites of ATP production in the mitochondria, but the molecules that are associated with the maintenance of cristae architecture still remain elusive.…”