Central Role of Mic10 in the Mitochondrial Contact Site and Cristae Organizing System (original) (raw)
Related papers
The EMBO Journal
Mitochondrial function is critically dependent on the folding of the mitochondrial inner membrane into cristae; indeed, numerous human diseases are associated with aberrant crista morphologies. With the MICOS complex, OPA1 and the F 1 F o-ATP synthase, key players of cristae biogenesis have been identified, yet their interplay is poorly understood. Harnessing super-resolution light and 3D electron microscopy, we dissect the roles of these proteins in the formation of cristae in human mitochondria. We individually disrupted the genes of all seven MICOS subunits in human cells and re-expressed Mic10 or Mic60 in the respective knockout cell line. We demonstrate that assembly of the MICOS complex triggers remodeling of pre-existing unstructured cristae and de novo formation of crista junctions (CJs) on existing cristae. We show that the Mic60-subcomplex is sufficient for CJ formation, whereas the Mic10-subcomplex controls lamellar cristae biogenesis. OPA1 stabilizes tubular CJs and, along with the F 1 F o-ATP synthase, fine-tunes the positioning of the MICOS complex and CJs. We propose a new model of cristae formation, involving the coordinated remodeling of an unstructured crista precursor into multiple lamellar cristae.
Cell Death & Differentiation, 2019
Mitochondrial cristae are critical for efficient oxidative phosphorylation, however, how cristae architecture is precisely organized remains largely unknown. Here, we discovered that Mic19, a core component of MICOS (mitochondrial contact site and cristae organizing system) complex, can be cleaved at N-terminal by mitochondrial protease OMA1 under certain physiological stresses. Mic19 directly interacts with mitochondrial outer-membrane protein Sam50 (the key subunit of SAM complex) and inner-membrane protein Mic60 (the key component of MICOS complex) to form Sam50-Mic19-Mic60 axis, which dominantly connects SAM and MICOS complexes to assemble MIB (mitochondrial intermembrane space bridging) supercomplex for mediating mitochondrial outer-and inner-membrane contact. OMA1-mediated Mic19 cleavage causes Sam50-Mic19-Mic60 axis disruption, which separates SAM and MICOS and leads to MIB disassembly. Disrupted Sam50-Mic19-Mic60 axis, even in the presence of SAM and MICOS complexes, causes the abnormal mitochondrial morphology, loss of mitochondrial cristae junctions, abnormal cristae distribution and reduced ATP production. Importantly, Sam50 displays punctate distribution at mitochondrial outer membrane, and acts as an anchoring point to guide the formation of mitochondrial cristae junctions. Therefore, we propose that Sam50-Mic19-Mic60 axis-mediated SAM-MICOS complexes integration determines mitochondrial cristae architecture.
Structural insights into crista junction formation by the Mic60-Mic19 complex
bioRxiv (Cold Spring Harbor Laboratory), 2022
Mitochondrial cristae membranes are the oxidative phosphorylation sites in cells. Crista junctions (CJs) form the highly curved neck regions of cristae and are thought to function as selective entry gates into the cristae space. Little is known about how CJs are generated and maintained. We show that the central coiled-coil (CC) domain of the mitochondrial contact site and cristae organizing system subunit Mic60 forms an elongated, bow tie-shaped tetrameric assembly. Mic19 promotes Mic60 tetramerization via a conserved interface between the Mic60 mitofilin and Mic19 CHCH (CC-helix-CC-helix) domains. Dimerization of mitofilin domains exposes a crescent-shaped membranebinding site with convex curvature tailored to interact with the curved CJ neck. Our study suggests that the Mic60-Mic19 subcomplex traverses CJs as a molecular strut, thereby controlling CJ architecture and function.
Journal of Molecular Biology, 2012
The mitochondrial inner membrane contains a large protein complex crucial for membrane architecture, the mitochondrial inner membrane organizing system (MINOS). MINOS is required for keeping cristae membranes attached to the inner boundary membrane via crista junctions and interacts with protein complexes of the mitochondrial outer membrane. To study if outer membrane interactions and maintenance of cristae morphology are directly coupled, we generated mutant forms of mitofilin/Fcj1 (formation of crista junction protein 1), a core component of MINOS. Mitofilin consists of a transmembrane anchor in the inner membrane and intermembrane space domains, including a coiled-coil domain and a conserved C-terminal domain. Deletion of the C-terminal domain disrupted the MINOS complex and led to release of cristae membranes from the inner boundary membrane, whereas the interaction of mitofilin with the translocase of the outer membrane (TOM) and the sorting and assembly machinery (SAM) were enhanced. Deletion of the coiled-coil domain also disturbed the MINOS complex and cristae morphology; however, the interactions of mitofilin with TOM and SAM were differentially affected. Finally, deletion of both intermembrane space domains disturbed MINOS integrity as well as interactions with TOM and SAM. Thus, the intermembrane space *Corresponding authors. Abbreviations used: Fcj1, formation of crista junction protein 1 (mitofilin); MINOS, mitochondrial inner membrane organizing system; Mio10, Mio27, mitochondrial inner membrane organization proteins of 10 and 27 kDa, respectively; SAM, sorting and assembly machinery; TOM, translocase of outer mitochondrial membrane. domains of mitofilin play distinct roles in interactions with outer membrane complexes and maintenance of MINOS and cristae morphology, demonstrating that MINOS contacts to TOM and SAM are not sufficient for the maintenance of inner membrane architecture.
2019
MICU1 is an EF-hand-containing mitochondrial protein that is essential for gating of the mitochondrial Ca 2+ uniporter channel (mtCU) and is reported to interact directly with the poreforming subunit, MCU and scaffold EMRE. However, using size-exclusion proteomics, we found that MICU1 exists in mitochondrial complexes lacking MCU. This suggests that MICU1 may have additional cellular functions independent of regulating mitochondrial Ca 2+ uptake. To discern mtCU-independent MICU1 functions, we employed a proteomic discovery approach using BioID2-mediated proximity-based (<10nm) biotinylation and subsequent LC-MS detection. The expression of a MICU1-BioID2 fusion protein in MICU1-/and MCU-/cells allowed the identification of total vs. mtCU-independent MICU1 interactors. Bioinformatics identified the Mitochondrial Contact Site and Cristae Organizing System (MICOS) components MIC60 (encoded by the IMMT gene) and Coiled-coil-helix-coiled-coil helix domain containing 2 (CHCHD2) as novel MICU1 interactors, independent of the mtCU. We demonstrate that MICU1 is essential for proper proteomic organization of the MICOS complex and that MICU1 ablation results in altered cristae organization and mitochondrial ultrastructure. We hypothesize that MICU1 serves as a MICOS calcium sensor, since perturbing MICU1 is sufficient to modulate cytochrome c release independent of mitochondrial Ca 2+ uptake across the inner mitochondrial membrane (IMM). Here, we provide the first experimental evidence suggesting that MICU1 regulates cellular functions independent of mitochondrial calcium uptake and may serve as a critical mediator of Ca 2+-dependent signaling to modulate mitochondrial membrane dynamics and cristae organization.
Trans-mitochondrial coordination of cristae at regulated membrane junctions
Nature Communications, 2015
Reminiscent of bacterial quorum sensing, mammalian mitochondria participate in interorganelle communication. However, physical structures that enhance or enable interactions between mitochondria have not been defined. Here we report that adjacent mitochondria exhibit coordination of inner mitochondrial membrane cristae at inter-mitochondrial junctions (IMJs). These electron-dense structures are conserved across species, resistant to genetic disruption of cristae organization, dynamically modulated by mitochondrial bioenergetics, independent of known inter-mitochondrial tethering proteins mitofusins and rapidly induced by the stable rapprochement of organelles via inducible synthetic linker technology. At the associated junctions, the cristae of adjacent mitochondria form parallel arrays perpendicular to the IMJ, consistent with a role in electrochemical coupling. These IMJs and associated cristae arrays may provide the structural basis to enhance the propagation of intracellular bioenergetic and apoptotic waves through mitochondrial networks within cells.