Biology subjects

Wiedemann, N.

Publications and source records attributed to Wiedemann, N..

5 recordsLinked to original sources

bioRxiv2026

Modular assembly of mitochondrial complex III from a dynamic matrix domain pool

Mitochondrial complex III is a central component of the cellular energy metabolism. It is an obligate dimer of catalytic and accessory subunits that are encoded by two genomes. How its large matrix domain, formed by the core proteins Qcr1 and Qcr2, is built and joined to the membrane part and during assembly is not known. Here we show that Qcr1 and Qcr2 preassemble independently of complex III into matrix domain modules. Cryo-EM structures from a cardiolipin-deficient yeast strain and of recombinant protein resolved single, double and triple matrix domains, which are linked by the C-terminal tail of Qcr1. In the mature complex III, the same tail binds cytochrome b and cardiolipin. The modules form a dynamic pool, in which assembly species interconvert and exchange subunits. Mutations at the module interfaces, including mimics of human disease variants, reshape this pool and deletion of the Qcr1 tail impairs respiratory growth. Substitution of a tyrosine residue linked to parkinsonism exposes a conserved cysteine residue to oxidation. A cryo-EM structure of an assembly intermediate shows a cap of two matrix domains bound to a monomeric membrane module of cytochrome b, Qcr7, Qcr8 and cytochrome c1. We propose that complex III receives its matrix domain from a dynamic pool of prebuilt modules, which organizes the dimerization of the complex.

biochemistry↗

bioRxiv2026

Super-resolution complexome of human mitochondria elucidates translocase, morphology and OXPHOS networks

Mitochondria function as cellular powerhouses and central hubs in metabolism, redox and stress reactions, signaling and apoptosis1-5. Defects of mitochondria lead to numerous human diseases1,6-8. The integration of mitochondrial proteins into complexes and networks is crucial for their function. Whereas the composition of the human mitochondrial proteome has been studied8,9, only limited information is available on the organization of the proteome into protein complexes and assemblies. Here we present a systematic mapping of the human mitochondrial complexome from HEK293T cells at super-resolution, resolving more than 7,000 abundance profile peaks of mitochondrial proteins. Proteins functioning in signaling, cell stress, protein biogenesis, turnover and membrane dynamics display particularly high complexities. High resolution and precise quantification enable discrimination between canonical constituents and non-stoichiometric regulatory interactors of the ATP synthase, major metabolite channels and import translocases. The complexome reveals membrane-spanning networks of protein insertase and morphology machinery, and co-assembly of protein import and export components at the major respiratory supercomplex, unraveling a multifunctional organization of mitochondrial machineries. This complexome represents a fully interactive resource for the systematic analysis of human mitochondrial machineries and interaction networks.

biochemistry↗

bioRxiv2026

A dynamic displacement mechanism drives protein import into mitochondria

Most mitochondrial proteins are produced in the cytosol and imported through the translocase of the outer mitochondrial membrane (TOM) to reach their final destination. Although this protein entry gate has been structurally characterized, it remains unclear how precursor proteins are handed off from the cytosolic receptor domains to the translocation pore. Here we show that the cytosolic domain of Tom22--traditionally viewed as the central TOM receptor--acts not as a structured scaffold but as a largely disordered, flexible segment that plays an active role in precursor transfer. Atomic-level structural techniques and in vivo experiments identified a conserved short linear motif that forms a transient !-helical element within this disordered domain. By binding to the canonical precursor protein binding sites of the receptors Tom20 and Tom70, this critical -helical segment acts as a precursor protein displacement element (PPDE). This competitive interaction facilitates the release of preproteins directly above the import pore, and thereby drives translocation across the outer mitochondrial membrane. These findings reveal that flexibility, rather than rigid structure, underlies the central transfer step of mitochondrial outermembrane protein translocation. Our results point to a versatile mechanism for ligand displacement in chaperone, receptor, and transport systems that must balance selective binding with efficient release.

cell biology↗

bioRxiv2025

Inconsistent Subthalamic Beta Expression in the Local Field Potential amid In- and Anti-Phasic Neuronal Bursts.

BackgroundElevated beta (12-32 Hz) activity in the local field potential (LFP) of the subthalamic nucleus (STN) is a hallmark of Parkinsons disease and closely tied to synchronized spiking. Albeit the biomarkers prevalence has not been independently and reliably assessed, it is employed to guide deep brain stimulation (DBS) lead implantation. Likewise, beta is under investigation to inform DBS programming and adaptive DBS. This study assesses the applicability of these efforts by quantifying the biomarkers prevalence and investigating its relationship to synchronized beta-bursting neurons. MethodsSTN LFP and spiking activity of n = 156 patients with Parkinsons disease from six DBS centers recorded via microelectrodes was examined. Spectral peaks in the LFPs were classified and the absence of artifacts confirmed. The distribution of phase angles between beta LFP and spiking of individual beta-bursting neurons were explored. FindingsBilateral beta LFP expression was observed in 47{middle dot}25% of patients, and in 65{middle dot}59% of hemispheres. LFP-synchronized neuronal spiking clustered in two-thirds of neurons at a primary and in one-third at a secondary LFP phase (182{middle dot}84{degrees} phase shifted). This applied on the group level and for individual patients across different DBS centers. InterpretationBeta-informed approaches mandate reliable biomarker expression, a requirement not met by slightly more than half of herein investigated patients. This is particularly troublesome for intraoperative guidance wherein the cause of biomarker absence, including DBS lead misplacement or a balanced ratio of phasic and antiphasic spiking neurons, cannot be determined, decreasing insight and increasing doubt. Although beta LFPs remain a valuable biomarker, routine clinical practice should not rely on beta alone; instead, multiple biomarkers (i.e. beta-gamma coupling, finely tuned gamma and/or cortico-cortical beta-band coupling) should be evaluated simultaneously to increase robustness. FundingMaximilian Scherer received funding from the Alexander von Humboldt-Foundation. Thomas Koeglsperger has been supported by the Munich Clinician Scientist Program.

neuroscience↗

bioRxiv2023

Role of the small protein Mco6 in the mitochondrial sorting and assembly machinery

The majority of mitochondrial precursor proteins are imported through the Tom40 {beta}-barrel channel of the translocase of the outer membrane (TOM). The sorting and assembly machinery (SAM) is essential for {beta}-barrel membrane protein insertion into the outer membrane and thus required for the assembly of the TOM complex. Here we demonstrate that the a-helical outer membrane protein Mco6 forms a complex with the mitochondrial distribution and morphology protein Mdm10 as part of the SAM machinery. Moreover, Mco6 also interacts with the subunit Mim1 of the mitochondrial import complex (MIM), which is itself required for the biogenesis of a-helical outer membrane proteins. MCO6 and MDM10 display a negative genetic interaction and a MCO6-MDM10 yeast double mutant contains reduced levels of TOM complex. Cells lacking Mco6 affect the levels of Mdm10 and MIM-subunits associated with assembly defects of the TOM complex. Thus, this work reveals a role of the SAMMco6 complex for the biogenesis of the mitochondrial outer membrane.

cell biology↗