Biology subjects

Eikmeier, N.

Publications and source records attributed to Eikmeier, N..

5 recordsLinked to original sources

bioRxiv2026

In the same cell, the proteome defines cellular state and the transcriptome marks transitions

Bulk transcriptome and proteome correlate only modestly, but this has not been investigated in the same cell or across cell-state changes. Here we introduce a scalable technology that quantifies thousands of proteins and transcripts in the same cell, separating RNA from protein by tip-based C18 capture and pairing full-length RNA sequencing with latest-generation mass spectrometry. In HeLa cells, transcript and protein abundances agree on the broad ranking within a cell (r = 0.45), but do not co-vary across the population (r = 0.038). In pluripotency transitions, only a third of matched transcripts and proteins change synchronously, yet the transcription factors defining each state stay tightly co-regulated. Transcript variance is several-fold larger than protein variance, reflecting transcriptional bursting and mRNA sampling noise. The proteome is thus the stable, low-noise definition of cell state, while the transcriptome marks cellular transitions; consequently, the proteome defines cell-state from far fewer cells.

systems biology↗

bioRxiv2026

Regulated conformational transitions in seipin define a functional ER–lipid droplet interface

Lipid droplets (LDs) are key organelles in cellular lipid homeostasis that form at the endoplasmic reticulum (ER) through a sequence of membrane rearrangements. While seipin emerged as an essential protein complex for LD biogenesis, how seipin-mediated LD formation proceeds beyond the initial step of neutral lipid nucleation remains unknown. Using a combination of in vitro and in-cell cryogenic electron microscopy (cryo-EM), ultrastructural expansion microscopy, molecular simulations and tailored genetic perturbations, we show that the seipin transmembrane domains undergo large-scale conformational rearrangements that define the architecture of the ER-LD interface and enable LD growth. Cryo-EM of purified Xenopus seipin revealed coexistence of two states: a compact "closed" conformation, consistent with early LD biogenesis, and an "open" conformation in which the transmembrane helices splay out laterally. Molecular dynamics simulations indicate that this open state induces local membrane curvature and promotes triacylglycerol accumulation. We identify conserved flexible linkers between the seipin luminal and transmembrane regions that act as mechanical hinges, enabling this conformational transition. We demonstrate that mutations in these hinge regions hinder seipin opening and affect LD formation in yeast and human cells. Analysis of native ER-LD contacts in human cells using light microscopy and cryo-electron tomography confirms that the seipin complex opens to establish stereotypical ~21-nm necks connecting the ER bilayer and LD monolayer. Moreover, we identify the liver-enriched microprotein SMLR1 as an inhibitor of this seipin conformational transition, providing a regulatory mechanism for seipin-dependent lipid storage in a tissue-specific manner. Together, these data establish seipin opening as a key structural rearrangement at the ER-LD interface that is essential for LD biogenesis and growth.

Cell Biology↗

bioRxiv2026

In situ polymerized monolith tips for reproducible, format-flexible proteomic sample preparation applied to biofluids

Sample preparation increasingly sets the throughput and reproducibility of mass spectrometry (MS)-based proteomics. StageTips (stop-and-go extraction tips) and variants thereof have long been common implements to purify samples, and we recently extended the concept to solid-phase extraction capture (SPEC) tips, in which the entire digestion takes place in sub-microliter volumes. Here we replace the hand-packed bed with a strong anion-exchange (SAX) monolith photopolymerized directly inside the pipette tip from a defined recipe (pSPEC). A liquid-handling robot casts 384 tunable tips in minutes, at low cost and in any format, adding negligibly to the workflows variance. Across biofluids, pSPEC added [~]20% more identifications than in-solution plasma and reached 3,500 protein groups from a single injection of healthy urine and 4,800 from saliva at 100 samples per day, depths usually requiring depletion or fractionation. The same light-cast chemistry should extend to single cells, affinity capture, and population-scale studies.

biochemistry↗

bioRxiv2026

Multimodal phenotyping defines variant-to-function maps for RBM20 in dilated cardiomyopathy

Multiplex assays of variant effects have linked thousands of genotypes to fitness effects, yet we lack profound understanding of how variants impact molecular phenotypes. Here, we introduce a deep mutational scanning framework that quantifies disease-determining molecular phenotypes in human cells, allowing readouts of protein localization and splicing regulatory function at scale. Applied to the dilated cardiomyopathy (DCM)-associated protein RBM20, we profiled [~]4,300 amino acid substitutions across disease-linked protein domains. Complemented by structure-function investigations of RBM20 bound to its nuclear import receptor TNPO3, we discover new variant hotspots affecting protein function. Finally, we systematically probed nuclear relocalization to identify variants that may be amenable to this therapeutic strategy. Together, we create comprehensive variant-to-function maps that predict variant impact, enhance clinical interpretation, and stratify RBM20-mediated DCM into mechanistically distinct therapeutic classes.

genomics↗

bioRxiv2026

Scanning DIA on the ZenoTOF 8600 system enables ultra-sensitive and quantitative proteomics from single cells to post-translational modifications in a compact platform

Mass spectrometry-based proteomics increasingly demands platforms that combine quantitative rigor with the discovery capabilities of accurate mass systems. Here we present the ZenoTOF 8600 system, a compact mass spectrometry system that integrates enhanced ion capture and transmission optics with an optical detection system, Zeno trap-enhanced MS/MS, electron-activated dissociation, and scanning quadrupole data-independent acquisition (ZT Scan DIA). We show that ZT Scan DIA outperforms conventional variable-window DIA (Zeno SWATH DIA) in both identifications and quantitative reproducibility, and demonstrate the platforms versatility across proteomics applications: thousands of protein groups from bulk samples at up to 500 samples per day, single-cell proteomics yielding up to 4,700 proteins, accurate ratio recovery in mixed-species quantitative benchmarks, low-attomole targeted quantitation, and detection of disease-relevant phosphorylation in a Parkinsons disease cellular model using complementary CID and EAD fragmentation. The instruments compact footprint makes it attractive for settings where both analytical breadth and operational robustness are required.

biophysics↗