Biology subjects

Marx, D.

Publications and source records attributed to Marx, D..

3 recordsLinked to original sources

bioRxiv2026

Structural order emerges without mechanical order inside living cells

Intracellular organization is vital for cell function, and disruption of organelle positioning is connected to severe diseases, such as cancer. Given the small length scale of cells and the importance of Brownian motion, maintaining intracellular organization requires mechanical interactions to remain stable. Here, we test the common view that intracellular organization is reflected in intracellular mechanical properties. Using the recently introduced active mechanical fingerprint, we quantify intracellular mechanical properties and active forces to create mechanical maps of patterned RPE1 cells. The organization of actin, microtubules, the Golgi apparatus, the endoplasmic reticulum, and the nucleus reveals pronounced structural polarization across the cell population. To overcome limitations of simple averages, we use a Wasserstein barycenter to calculate an optimal intracellular organization that explains all measurements with minimal cellular distortion. To our surprise, and in contrast to previous reports, we find neither a statistically significant spatial mechanical pattern nor any relevant correlation between the tested structures and intracellular mechanical properties. While there is clear local mechanical anisotropy, the large heterogeneity of mechanical values outweighs any intracellular mechanical gradient. This is further supported by large cell-to-cell variability. Thus, despite having the same genome, cells function properly while their intracellular mechanical properties vary over two orders of magnitude.

biophysics↗

bioRxiv2026

Metal-induced energy transfer uncovers activation-induced axial reorganization of signaling complexes inside cells

Transmembrane signaling mediated by cytokine receptors orchestrates key cellular processes such as proliferation, differentiation, and immune responses. While numerous high-resolution structures of cytokine receptor ectodomains are available, the structural organization of the largely disordered intracellular domain (ICD) has remained unclear. Here, we interrogate the axial organization of cytokine receptor signaling complexes at the plasma membrane by metal-induced energy transfer (MIET). For this purpose, we leveraged biofunctionalized nanodot arrays (bNDAs) to capture cell surface receptors at a defined distance from the substrate. Readout by fluorescence lifetime imaging microscopy enabled quantifying axial distances of proteins in the plasma membrane of cells at both ensemble and single-molecule levels with a resolution of [~]1 nm. Using the prototypic, biomedically relevant class I cytokine receptor GP130 as a model system, we uncover by MIET that the ICD extends randomly into the cytosol in the resting state, but surprisingly undergoes an axial compaction upon signal activation. These results demonstrate the potential of bNDA-supported MIET for resolving the axial architecture of signaling complexes within the cellular context.

biophysics↗

bioRxiv2023

Structural basis of allosteric modulation ofmetabotropic glutamate receptor activation and desensitization

The metabotropic glutamate receptors (mGluRs) are neuromodulatory family C G protein coupled receptors which assemble as dimers and allosterically couple extracellular ligand binding domains (LBDs) to transmembrane domains (TMDs) to drive intracellular signaling. Pharmacologically, mGluRs can be targeted either at the LBDs by glutamate and synthetic orthosteric compounds or at the TMDs by allosteric modulators. Despite the potential of allosteric TMD-targeting compounds as therapeutics, an understanding of the functional and structural basis of their effects on mGluRs is limited. Here we use a battery of approaches to dissect the distinct functional and structural effects of orthosteric versus allosteric ligands. We find using electrophysiological and live cell imaging assays that both agonists and positive allosteric modulators (PAMs) can drive activation and desensitization of mGluRs. The effects of PAMs are pleiotropic, including both the ability to boost the maximal response to orthosteric agonists and to serve independently as desensitization-biased agonists across mGluR subtypes. Conformational sensors reveal PAM-driven inter-subunit re-arrangements at both the LBD and TMD. Motivated by this, we determine cryo-electron microscopy structures of mGluR3 in the presence of either an agonist or antagonist alone or in combination with a PAM. These structures reveal PAM-driven re-shaping of intra- and inter-subunit conformations and provide evidence for a rolling TMD dimer interface activation pathway that controls G protein and beta-arrestin coupling. Highlights-Agonists and PAMs drive mGluR activation, desensitization, and endocytosis -PAMs are desensitization-biased and synergistic with agonists -Four combinatorial ligand conditions reveal an ensemble of full-length mGluR structures with novel interfaces -Activation and desensitization involve rolling TMD interfaces which are re-shaped by PAM

biophysics↗