Biology subjects

Bock-Bierbaum, T.

Publications and source records attributed to Bock-Bierbaum, T..

5 recordsLinked to original sources

bioRxiv2026

Exploring the activation mechanism of the Mic60 subcomplex governing mitochondrial crista junctions

Crista junctions (CJs) are narrow infoldings of the inner mitochondrial membrane, serving as entry points into the cristae microenvironment. The mitochondrial contact site and cristae organizing system (MICOS) complex is a highly conserved protein machinery controlling CJ biogenesis and architecture, but its assembly mechanism driving CJ formation has remained unclear. By determining a crystal structure of a Chaetomium thermophilum Mic60-Mic19 complex and combining it with modelling and mutagenesis studies, we identify an extended helical region (EHR) of the Mic60 mitofilin domain and a further Mic19 helix as crucial elements of complex formation. In vitro cross-linking data and hydrogen-deuterium exchange mass spectrometry resolve domain assembly and conformational dynamics of the Mic60 Mic19 subcomplex and point to the EHR as a molecular switch controlling Mic60 transition from a closed dimer to a Mic19-bound hetero-octamer. Our data provide a structural model for Mic60 activation and therefore MICOS assembly as a prerequisite for crista junction formation.

molecular biology↗

bioRxiv2025

Structural studies suggest CCDC127 as a novel membrane contact site protein in the mitochondrial intermembrane space

Mitochondria feature a sophisticated membrane architecture, with a planar mitochondrial outer membrane (MOM) and a folded inner membrane (MIM). Due to the remarkable adaptability of mitochondria, a proteinaceous network in the intermembrane space (IMS) was proposed to confer both stability and flexibility. However, components of such scaffolds, tentatively termed the mitoskeleton, have remained largely elusive. The mitochondrial contact site and organizing system (MICOS), a central organizer of mitochondrial membrane architecture, was suggested to participate in mitoskeleton formation. Here, we structurally characterize the coiled-coil domain-containing 127 (CCDC127) protein, a putative interactor of MICOS. We show that CCDC127s amino-terminal transmembrane region is anchored in the MOM and the bulk soluble part exposed to the IMS. A crystal structure of CCDC127s central coiled-coil displays a parallel dimer which further oligomerizes into tetramers. We demonstrate that the carboxy-terminal helical bundle (CHB) domain dimerizes to create a peripheral membrane-binding site. Supported by electron microscopy data, we propose a structural model of CCDC127 as intramitochondrial membrane contact site protein mediating the structural organization of the IMS as part of the mitoskeleton.

molecular biology↗

bioRxiv2025

Topology control by a conserved cysteine pair in the OMM-protein CCDC127 enables MICOS interaction

Mitochondrial disulfide relay substrates beyond the canonical substrates remain incompletely defined. Revisiting the human MIA40 interactome with enhanced depth, we identified CCDC127 as a previously unrecognized substrate candidate. CCDC127 contains a single transmembrane segment and a conserved C-terminal helical bundle domain (CHB). Comprehensive proteomic and biochemical analyses revealed that, contrary to earlier reports, CCDC127 adopts an Nout-Cin topology in the outer mitochondrial membrane (OMM) with its CHB residing in the intermembrane space (IMS). CCDC127 undergoes oxidation by the disulfide relay, forming a long-range intramolecular disulfide bond between C174 and C219. Loss of these cysteines disrupts correct OMM insertion, inverts transmembrane topology and triggers proteasome-dependent degradation, establishing the disulfide as a key determinant of CCDC127 maturation. Interactome analyses identified MICOS components--particularly the MIC60/MIC19 module--as major partner proteins required for the stability of large oligomeric CCDC127 complexes. CCDC127 deficiency impaired cellular proliferation, influenced phospholipid levels, and caused grossly altered cristae morphology. Together, CCDC127 emerges as a MICOS-associated OMM protein essential for mitochondrial membrane organization and lipid homeostasis.

biochemistry↗

bioRxiv2025

Detergent-free reconstitution of transmembrane proteins in giant liposomes of complex curvature by the Synthetic Membrane Transfer

Transmembrane proteins perform many crucial functions in the cell, including transfer of matter and information across the membrane. Giant Unilamellar Vesicles (GUVs) are the ideal tool for studying these processes; yet functional transmembrane protein reconstitution in GUVs still represents a bottleneck in bottom-up synthetic biology. Here, we developed a novel approach that we call Synthetic Membrane Transfer (SMT), where transmembrane proteins reconstituted into styrene-maleic acid particles in a detergent-free environment can be transferred to the GUV membrane. The SMT approach is a one-step, facile and general method that works for structurally diverse proteins, and it does not require any specific lipid or buffer composition. Moreover, the SMT is fully compatible with the Synthetic Membrane Shaper (SMS) technology, which allows to deform GUVs in a controlled fashion, obtaining dumbbell-shaped GUVs exhibiting a catenoid-like geometry. The combination of SMT and SMS results in functional reconstitution of transmembrane proteins in catenoid membrane necks. Using this approach, we demonstrate that Mic10, a component of the MICOS complex, directly senses membrane curvature and localizes at the neck of dumbbells GUVs, a geometry that recapitulates the shape of mitochondria cristae junctions. This paves the way for bottom-up reconstitution of the MICOS complex on a physiological membrane geometry.

synthetic biology↗

bioRxiv2022

Structural insights into crista junction formation by the Mic60-Mic19 complex

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 domain of the mitochondrial contact and cristae organizing system (MICOS) 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 domains. Dimerization of mitofilin domains exposes a crescent-shaped membrane-binding site with convex curvature tailored to interact with curved CJ necks. Our study suggests that the Mic60-Mic19 subcomplex transverses CJs as a molecular strut, thereby controlling CJ architecture and function.

cell biology↗