Biology subjects

Meinecke, M.

Publications and source records attributed to Meinecke, M..

7 recordsLinked to original sources

bioRxiv2025

Membrane curvature regulates Ups1 dependent phosphatidic acid transfer across lipid bilayers

Mitochondria are essential organelles in eukaryotic cells, enclosed by two membranes with distinct compositions and functions. In addition to the endoplasmic reticulum, mitochondria are major sites of cellular lipid production. Cardiolipin, for example, is exclusively synthesized in the mitochondrial inner membrane. This requires the precursor lipid phosphatidic acid to be imported from the endoplasmic reticulum to the mitochondrial outer membrane. Subsequently phosphatidic acid is transferred to the inner membrane by the lipid transfer protein Ups1/PRELID1. The regulation of this process, the role of membrane physico-chemical properties, and the mechanisms by which energy barriers are overcome during lipid extraction and insertion remain poorly understood. Here, we demonstrate that Ups1 exhibits a strong preference for binding to positively curved membrane regions. Our findings reveal that phosphatidic acid extraction is energetically favored at these membrane domains, leading to enhanced lipid transfer between membranes with high positive curvature and we show that events at the donor membrane are rate limiting for the transfer cycle. Our data suggest that Ups1 membrane binding is modulated by pH, lipid composition, and membrane morphology, pointing to a complex, multipartite regulatory network underlying intra-mitochondrial lipid transfer.

biochemistry↗

bioRxiv2025

The core MICOS complex subunit Mic60 has been substituted by two cryptic mitofilin-containing proteins in Euglenozoa

Cristae enclose respiratory chain complexes, making them the bioenergetic subcompartments of mitochondria. The MICOS complex is among the inducers of membrane curvature needed for crista formation. Resembling the respiratory chain complexes, MICOS is organized around a core protein, the mitofilin-domain bearing Mic60, that was inherited from the alphaproteobacterial progenitor of mitochondria. Extant alphaproteobacteria express Mic60 to form their own bioenergetic subcompartments, demonstrating the permeance of Mic60s form and function during prokaryotic and eukaryotic evolution. Yet, unlike virtually all aerobic eukaryotes, Mic60 is not encoded within the genomes of the multifarious protists that comprise the phylum Euglenozoa, including trypanosomes. Here, we show that Mic60 has been replaced in euglenozoans by two cryptic mitofilin domain-containing MICOS subunits, Mic34 and Mic40. Contrasting alphaproteobacterial and mitochondrial Mic60, these are not integral membrane proteins. Mic34 and Mic40 are as diverged from each other as both are to canonical Mic60. Reverse genetics revealed they are intertwined with the oxidative protein folding pathway required for mitochondrial-and crista-biogenesis, veiling a potential membrane remodeling role. Nevertheless, Mic34 binds phospholipid bilayers in vitro. Mic34 and Mic40 heterologous expression remodels gammaproteobacterial cytoplasmic membranes, like Mic60. Unexpectedly, Mic34 overexpression elaborates the simplified tubular mitochondrion of a Trypanosoma brucei life cycle stage with repressed oxidative phosphorylation. Furthermore, this activity was ablated by mutations to Mic34s mitofilin domain that correspond to essential motifs found in yeast Mic60s mitofilin domain. Thus, the mitofilin protein family is more diverse than originally supposed, with two of its structurally most divergent members altering the core of euglenozoan MICOS.

molecular biology↗

bioRxiv2023

The Drosophila MIC10 orthologue has a propensity to polymerize into cristae-shaping filaments

Mitochondria are essential eukaryotic double-membrane organelles. The convoluted mitochondrial inner membrane forms highly organized invaginations, termed cristae, which are crucial for energy metabolism. Cristae formation requires MICOS, a conserved hetero-oligomeric inner membrane complex. The MICOS core subunit MIC10 is a small transmembrane protein that oligomerizes through highly conserved glycine-rich motifs to control cristae formation. Sequence alignments show that D. melanogaster exhibits three MIC10-like proteins with different tissue-specific expression patterns. Here, we show that the ubiquitously expressed Dmel_CG41128/MINOS1b/DmMIC10b is the major MIC10 orthologue in flies. Loss of DmMIC10b disturbs cristae architecture of mitochondria and reduces the life-span and fertility of flies. Moreover, using fluorescence nanoscopy and electron tomography, we demonstrate that despite its high similarity to the MIC10 proteins from yeast and humans, DmMIC10b exhibits the unique ability to polymerize into elongated filaments upon overexpression. DmMIC10b filaments form bundles which accumulate in the intermembrane space and alter the shape of mitochondrial cristae membranes. We show that the formation of the filaments relies on conserved glycine and cysteine residues and is suppressed by co-expression of other MICOS proteins. Thereby, our findings provide new insights into the regulation of MICOS in flies.

cell biology↗

bioRxiv2022

Metamorphic proteins at the basis of human autophagy initiation and lipid transfer

Autophagy is a conserved intracellular degradation pathway that uses de novo doublemembrane vesicle (autophagosome) formation to target a wide range of cytoplasmic material for lysosomal degradation. In multicellular organisms, autophagy initiation requires the timely assembly of a contact site between the ER and the nascent autophagosome. Here, we report the in vitro reconstitution of a full-length sevensubunit human autophagy initiation supercomplex and found at its core ATG13-101 and transmembrane protein ATG9. Assembly of this core complex requires the rare ability of ATG13 and ATG101 to adopt topologically distinct folds. The slow spontaneous conversion between folds creates a rate-limiting step to regulate selfassembly of the super-complex. The interaction of the core complex with ATG2-WIPI4 enhances tethering of membrane vesicles and accelerates lipid transfer of ATG2 by both ATG9 and ATG13-101. Our work uncovers the molecular basis of the contact site and its assembly mechanisms imposed by the metamorphosis of ATG13-101 to regulate autophagosome biogenesis in space and time.

biochemistry↗

bioRxiv2022

Membrane interactions of mitochondrial lipid transfer proteins

The mitochondrial inner membrane is an integral part of the cellular lipid biosynthesis network. Intramitochondrial lipid transfer shuttles specific lipid species between the two mitochondrial membranes. This pathway is facilitated by designated protein complexes in the intermembrane space. A hetero-dimeric complex of Ups1 and Mdm35 has been identified in yeast to transfer phosphatidic acid from the outer to the inner membrane. Here, we define pH and lipid charge dependency of Ups1 membrane interaction. We show that Ups1 interacts with membranes in a membrane curvature dependent manner. Ups1 predominantly binds to membrane domains of positive curvature. Desorption of phosphatidic acid from positively curved membranes is energetically favorable over flat or negatively curved membranes. Hence, our results demonstrate that Ups1 specifically binds to membrane regions where extraction and insertion of lipids is enhanced.

biophysics↗

bioRxiv2021

Regulation of mitochondrial proteostasis by the proton gradient

Mitochondria adapt to different energetic demands reshaping their proteome. Mitochondrial proteases are emerging as key regulators of these adaptive processes. Here, we use a multi-proteomic approach to demonstrate regulation of the m-AAA protease AFG3L2 by the mitochondrial proton gradient, coupling mitochondrial protein turnover to the energetic status of mitochondria. We identify TMBIM5 (previously also known as GHITM or MICS1) as a Ca2+/H+ exchanger in the mitochondrial inner membrane, which binds to and inhibits the m-AAA protease. TMBIM5 ensures cell survival and respiration, allowing Ca2+ efflux from mitochondria and limiting mitochondrial hyperpolarization. Persistent hyperpolarization, however, triggers degradation of TMBIM5 and activation of the m-AAA protease. The m-AAA protease broadly remodels the mitochondrial proteome and mediates the proteolytic breakdown of respiratory complex I to confine ROS production and oxidative damage in hyperpolarized mitochondria. TMBIM5 thus integrates mitochondrial Ca2+ signaling and the energetic status of mitochondria with protein turnover rates to reshape the mitochondrial proteome and adjust the cellular metabolism.

molecular biology↗

bioRxiv2020

Cooperativity of membrane-protein and protein-protein interactions control membrane remodeling by epsin 1 and regulate clathrin-mediated endocytosis

Membrane remodeling is a critical process for many membrane trafficking events, including clathrin-mediated endocytosis. Several molecular mechanisms for protein induced membrane curvature have been described in some detail. Contrary, the effect that the physico-chemical properties of the membrane has on these processes is far less well understood. Here, we show that the membrane binding and curvature-inducing ENTH domain of epsin1 is regulated by phosphatidylserine (PS). ENTH binds to membranes in a PI(4,5)P2-dependent manner but only induces curvature in the presence of PS. On PS-containing membranes, the ENTH domain forms rigid homo-oligomers and assembles into clusters. Membrane binding and membrane remodeling can be separated by structure-to-function mutants. Such oligomerization mutants bind to membranes but do not show membrane remodeling activity. In vivo they are not able to rescue defects in epidermal growth factor receptor (EGFR) endocytosis in epsin knock-down cells. Together, these data show that the membrane lipid composition is important for the regulation of protein-dependent membrane deformation during clathrin-mediated endocytosis.

biophysics↗