Biology subjects

Hagn, F.

Publications and source records attributed to Hagn, F..

4 recordsLinked to original sources

bioRxiv2026

The Conserved N-Terminal Extension of AtKEA1 Is Largely Dispensable for Plastid Function but Contributes to Potassium Homeostasis

Members of the K efflux antiporter (KEA) family fulfill key roles in plastids and the endomembrane system. Plants and green algae possess at least one KEA mediating K/H exchange across the plastid inner envelope (IE) membrane. Recently, IE KEAs were shown to be essential for plastid gene expression (PGE), chloroplast development, and photosynthesis. Plants lacking these antiporters exhibit reduced stromal protein synthesis and accumulation of unprocessed rRNA precursors. KEA proteins comprise a conserved monovalent cation/proton antiporter 2 (CPA2) domain and a regulatory K transport and NAD-binding (KTN) domain. IE KEAs are distinguished by an additional [~]500-amino-acid N-terminal extension containing a coiled-coil (CC) domain embedded within a largely intrinsically disordered region (IDR). Intrigued by this unusual architecture, we performed phylogenetic analyses, revealing that this N-terminal fusion arose early and has been conserved throughout the green lineage. We then investigated the oligomeric state, native distribution, and function of the N-terminal domain. Using Arabidopsis thaliana, we found that IE KEAs localize to discrete clusters within the inner envelope membrane and assemble into complexes of approximately 600 kDa. Finally, complementary approaches using a functional KEA1 variant lacking the core N-terminal domains (KEA1{Delta}N) indicate that this extension plays a regulatory rather than an essential role. Our findings uncover an evolutionarily ancient regulatory module that shapes the molecular organization and function of IE KEAs, advancing our understanding of plastid ion and pH homeostasis and plastid ribosome integrity. One-sentence summaryPlastid KEA1/2 proteins feature a unique N-terminal extension that modulates potassium transport activity in a yet unknown manner but is not essential for normal plant growth under ambient conditions.

plant biology↗

bioRxiv2025

Integrative Biophysical Illumination of the 3D GPCRome Dynamics

Achieving high-resolution insights into protein dynamics remains a major challenge, particularly for membrane proteins such as G protein-coupled receptors (GPCRs) - a highly dynamic class of cell surface receptors and key drug targets. Here, we present an integrative strategy that bridges computational and experimental biophysical methods for probing protein dynamics. To illustrate its potential, we developed GPCRmd-NMR, a platform that synergistically combines molecular dynamics (MD) simulations with high-resolution nuclear magnetic resonance (NMR) spectroscopy across the 3D GPCRome. The resulting dataset maps over 20 billion NMR signals to more than 7 million conformational snapshots of GPCRs, enabling structure-resolved analysis at an unprecedented scale. Application across multiple GPCRs provides access to previously underexplored functional GPCR dynamics, receptor states, and sites, including microswitches and hidden ligand entrance gateways. Our integrated framework offers a powerful solution to long-standing challenges faced by both experimental and computational researchers. To support broad accessibility, GPCRmd-NMR is available as an open-access, web-based framework equipped with user-friendly analysis tools (https://www.gpcrmd.org/gpcrmd-nmr-tool) and is readily applicable to other dynamic protein families beyond GPCRs and other types of biophysical data.

bioinformatics↗

bioRxiv2020

Cryo-EM structure of an activated GPCR-G protein complex in lipid nanodiscs

G protein coupled receptors (GPCRs) are the largest superfamily of transmembrane proteins and the targets of over 30% of currently marketed pharmaceuticals1,2. Although several structures have been solved for GPCR-G protein complexes3-17, structural studies of the complex in a physiological lipid membrane environment are lacking. Additionally, most previous studies required additional antibodies/nanobodies and/or engineered G proteins for complex stabilization. In the absence of a native complex structure, the underlying mechanism of G protein activation leading to GDP/GTP exchange remains unclear. Here, we report cryo-EM structures of lipid bilayer-bound complexes of neurotensin, neurotensin receptor 1, and Gi1{beta}1{gamma}1 protein in two conformational states, resolved to 4.1 and 4.2 [A] resolution. The structures were determined without any stabilizing antibodies/nanobodies, and thus provide a native-like platform for understanding the structural basis of GPCR-G protein complex formation. Our structures reveal an extended network of protein-protein interactions at the GPCR-G protein interface compared to in detergent micelles, defining roles for the lipid membrane in modulating the structure and dynamics of complex formation, and providing a molecular explanation for the stronger interaction between GPCR and G protein in lipid bilayers. We propose a detailed allosteric mechanism for GDP release, providing new insights into the activation of G proteins for downstream signaling under near native conditions.

molecular biology↗

bioRxiv2019

Intramembrane cleavage of TREM2 is determined by its intrinsic structural dynamics

Sequence variants of the microglial expressed TREM2 (triggering receptor expressed on myeloid cells 2) are a major risk factor for late onset Alzheimers disease. TREM2 requires a stable interaction with DAP12 in the membrane to initiate signaling, which is terminated by TREM2 ectodomain shedding and subsequent intramembrane cleavage by {gamma}-secretase. To understand the structural basis for the specificity of the intramembrane cleavage event, we determined the solution structure of the TREM2 transmembrane helix (TMH). Due to the presence of a charged amino acid in the membrane region the TREM2-TMH adopts a kinked structure with increased flexibility. Charge removal leads to TMH stabilization and reduced dynamics, similar to its structure in complex with DAP12. Strikingly, these dynamical features perfectly correlate with the site of the initial {gamma}-secretase cleavage event. These data suggest an unprecedented cleavage mechanism by {gamma}-secretase where flexible TMH regions are identified to initiate substrate cleavage.

neuroscience↗