Tim22, the Essential Core of the Mitochondrial Protein Insertion Complex, Forms a Voltage-Activated and Signal-Gated Channel

Kovermann, Peter; Truscott, Kaye N.; Guiard, Bernard; Rehling, Peter; Sepuri, Naresh Babu V.; Müller, H.; Jensen, Robert E.; Wagner, Richard; Pfanner, Nikolaus

doi:10.1016/s1097-2765(02)00446-x

Cited by 151 publications

(128 citation statements)

References 46 publications

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“…Tim22 is the core channel of the metabolite carrier translocase complex. [65][66][67][68] Tim22 has a dynamic pore size ranging from 1.1 to 1.8 nm, which is still below the size of granzyme. How Tim22 releases the cargo protein into the lipid bilayer is still unknown, but likely involves conformational changes that could be exploited by hijacker proteins such as granzymes.…”

Section: Discussionmentioning

confidence: 98%

Granzyme B enters the mitochondria in a Sam50-, Tim22- and mtHsp70-dependent manner to induce apoptosis

et al. 2017

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We have found that granzyme B (GB)-induced apoptosis also requires reactive oxygen species resulting from the alteration of mitochondrial complex I. How GB, which does not possess a mitochondrial targeting sequence, enter this organelle is unknown. We show that GB enters the mitochondria independently of the translocase of the outer mitochondrial membrane complex, but requires instead Sam50, the central subunit of the sorting and assembly machinery that integrates outer membrane β-barrel proteins. Moreover, GB breaches the inner membrane through Tim22, the metabolite carrier translocase pore, in a mitochondrial heat-shock protein 70 (mtHsp70)-dependent manner. Granzyme A (GA) and caspase-3 use a similar route to the mitochondria. Finally, preventing GB from entering the mitochondria either by mutating lysine 243 and arginine 244 or depleting Sam50 renders cells more resistant to GB-mediated reactive oxygen species and cell death. Similarly, Sam50 depletion protects cells from GA-, GM-and caspase-3-mediated cell death. Therefore, cytotoxic molecules enter the mitochondria to induce efficiently cell death through a noncanonical Sam50-, Tim22-and mtHsp70-dependent import pathway.Cytotoxic lymphocytes eradicate pathogen-infected or transformed cells mainly through the cytotoxic granule pathway. [1][2][3][4] Among the five human granzymes (A, B, H, K and M), granzyme B (GB) triggers cell death in both a caspasedependent and caspase-independent manner, although human and mouse GB differ in their requirement for caspase activation. 5-10 GB-induced cell death also involves Bid/Bax/ Bak-mediated mitochondrial outer membrane permeabilization for the release of the apoptogenic factors cytochrome c, Smac/Diablo, Endo G, HtrA2 and AIF. 1,9-17 We have recently reported that mitochondrial reactive oxygen species (ROS) have a critical role in GB pathway by amplifying apoptogenic factor release, oligonucleosomal DNA fragmentation and lysosomal membrane rupture. 18 Mitochondrial ROS resulted from GB-mediated cleavage of NDUFV1, NDUFS1 and NDUFS2, three subunits of mitochondrial complex I. 18 How GB that does not possess a mitochondrial targeting sequence enters the mitochondria is not known. The mitochondrial nucleoid encodes only for 13 structural proteins, while the rest of the mitochondrial proteome is nuclear-encoded and transported to the mitochondria through a sophisticated protein import machinery. [19][20][21][22][23][24][25][26][27][28] The translocase of the outer mitochondrial membrane (TOM), the entry gate to the mitochondria, 20 passes on the cargos to the sorting and assembly machinery (SAM) complex, to the mitochondrial intermembrane space assembly (MIA) complex and to the translocases of the inner mitochondrial membrane TIM22 or TIM23 complexes for delivery to the outer membrane, the intermembrane space, the inner membrane or the matrix, respectively. [19][20][21][22]25,26,28 Unexpectedly, we found that GB mitochondrial entry is independent of the TOM-TIM23 complexes, but requires instead the Sam50 and Tim22 chann...

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Section: Discussionmentioning

confidence: 98%

Granzyme B enters the mitochondria in a Sam50-, Tim22- and mtHsp70-dependent manner to induce apoptosis

et al. 2017

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“…For efficient translocation of proteins across the mitochondrial membranes, mitochondrial precursor proteins are kept in a relatively unfolded state to squeeze through the narrow pores formed by tightly gated translocons (Kovermann et al 2002;Paschen et al 2003;Rehling et al 2003). In this unfolded state, precursor proteins have an increased chance of exposing hydrophobic regions promoting unwanted protein-protein interactions or cause them to aggregate, however these unwanted effects are typically overcome through the action of chaperones (Fig.…”

Section: Mitochondrial Quality Controlmentioning

confidence: 99%

Quality Control of Mitochondrial Proteostasis

Baker

Tatsuta²,

Langer

2011

Cold Spring Harbor Perspectives in Biology

225

193

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A decline in mitochondrial activity has been associated with aging and is a hallmark of many neurological diseases. Surveillance mechanisms acting at the molecular, organellar, and cellular level monitor mitochondrial integrity and ensure the maintenance of mitochondrial proteostasis. Here we will review the central role of mitochondrial chaperones and proteases, the cytosolic ubiquitin-proteasome system, and the mitochondrial unfolded response in this interconnected quality control network, highlighting the dual function of some proteases in protein quality control within the organelle and for the regulation of mitochondrial fusion and mitophagy.

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“…After translocation, preproteins of the metabolite carrier family are bound in the intermembrane space by the Tim9-Tim10 complex (24 -30). Subsequent insertion of carrier proteins into the inner membrane by the Tim22 complex requires the electrochemical gradient across this membrane (31)(32)(33)(34)(35).…”

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confidence: 99%

Hsp90 Functions in the Targeting and Outer Membrane Translocation Steps of Tom70-mediated Mitochondrial Import

Fan

Bhangoo

Young

2006

Journal of Biological Chemistry

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The Tom70 import receptor on the mitochondrial outer membrane specifically recognizes Hsp90 and Hsc70, a critical step for the import of mitochondrial preproteins, the targeting of which depends on these cytosolic chaperones. To analyze the role of Hsp90 in mitochondrial import, the effects of the Hsp90 inhibitors geldanamycin and novobiocin were compared. Geldanamycin occludes the N-terminal ATP-binding site of Hsp90, whereas novobiocin targets the C-terminal region of the chaperone. Here, novobiocin was found to inhibit preprotein import and, in particular, targeting to the purified cytosolic fragment of Tom70. Hsp90 cross-linking to preprotein and coprecipitation of Hsp90 with Tom70 were both impaired by novobiocin. Overall, novobiocin treatment increased preprotein aggregation, contributing to reduced import competence. In contrast, geldanamycin had no apparent effect on preprotein interactions with Hsp90, formation of preprotein-chaperone complexes, Hsp90 docking onto Tom70, or preprotein association with the outer membrane. Instead, geldanamycin impaired formation of preprotein import intermediates at the outer membrane. This suggests a novel active role for Hsp90 in import steps subsequent to Tom70 targeting. Our results outline the mechanisms of Hsp90 function in preprotein targeting and transport.The great majority of mitochondrial proteins are encoded in the nucleus, translated by cytosolic ribosomes, and imported into mitochondria by a translocation apparatus located in the mitochondrial outer and inner membranes (1). The TOM (translocase of the mitochondrial outer membrane) complex contains import receptors that mediate the targeting of preproteins to the membrane and a general import pore complex through which preproteins are translocated. Sorting of preproteins to their appropriate final compartment within the mitochondria is performed by the TIM (translocase of the inner membrane) machinery (2, 3).Before import, unfolded or hydrophobic mitochondrial preproteins are bound by cytosolic chaperones, notably Hsc70 (heat shock cognate protein of 70 kDa; the constitutive Hsp70 (heat shock protein of 70 kDa) form in mammals) and Hsp90. Such preproteins include members of the inner membrane metabolite carrier family. The integral membrane Tom70 import receptor contains a tetratricopeptide repeat (TPR) 3 domain similar to those found in several other cytosolic cochaperones of Hsp90 and Hsc70 and provides a specific docking site for the Hsp90 and Hsc70 chaperones. This interaction is thought to be an essential first step in Tom70-dependent preprotein targeting, followed by contact between the preprotein and Tom70 itself (4 -15). Additional cytosolic proteins, including co-chaperones of , might also interact with preproteins to further assist import. After targeting to Tom70, preproteins are translocated through the outer membrane via the Tom40 import pore complex. The Tom40 pore also translocates preproteins targeted through the major import receptor Tom20 (21-23). After translocation, preproteins of the met...

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Tim22, the Essential Core of the Mitochondrial Protein Insertion Complex, Forms a Voltage-Activated and Signal-Gated Channel

Cited by 151 publications

References 46 publications

Granzyme B enters the mitochondria in a Sam50-, Tim22- and mtHsp70-dependent manner to induce apoptosis

Granzyme B enters the mitochondria in a Sam50-, Tim22- and mtHsp70-dependent manner to induce apoptosis

Quality Control of Mitochondrial Proteostasis

Hsp90 Functions in the Targeting and Outer Membrane Translocation Steps of Tom70-mediated Mitochondrial Import

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