Biology subjects

Schnapp, G.

Publications and source records attributed to Schnapp, G..

3 recordsLinked to original sources

bioRxiv2025

AXL-GAS6/PROS1 Interaction: A Critical Switch Between Aberrant- and Healthy Repair Following Alveolar Lung Injury

RationaleIdiopathic pulmonary fibrosis (IPF) is a progressive lung disease characterized by aberrant alveolar repair and excessive fibrosis. The TAM-family receptor tyrosine kinase AXL, activated by GAS6 and PROS1, is implicated in tissue remodeling, but ligand-specific AXL signaling during alveolar repair remains poorly defined. ObjectivesTo investigate ligand specific AXL signaling in IPF and how it impacts epithelial proliferation and repair after alveolar injury in-vivo and in-vitro. MethodsSingle cell RNA sequencing was utilized to understand cell specific expression patterns in IPF patients, followed by functional studies in primary human cell culture and functional spatial digital profiling (FuncOmap) analysis in patient tissue. Longitudinal assessment of repair process after alveolar-specific injury in-vivo was used to complement the in-vitro approach. ResultsAXL expression showed enrichment in basal and aberrant basaloid cells of IPF patients. In-vitro GAS6 increased proliferation of basal cells, while PROS1 counteracted this effect. FuncOmap analysis demonstrates direct in-situ interactions between AXL and both ligands, providing evidence for biological relevance. Investigating longitudinal repair processes in-vivo revealed dynamic regulation of AXL ligands as well as AXL. ConclusionsThese findings highlight the importance of ligand-specific AXL signaling in lung repair and suggest that it dysregulation may contribute to IPF pathogenesis, offering potential therapeutic targets for restoring normal repair processes.

molecular biology↗

bioRxiv2025

Small molecule-controlled gene expression: Design of drug-like high affinity small molecule modulators of a custom-made riboswitch

Riboswitches are regulatory RNA structures that modulate gene expression in response to a small molecule. Until now, efforts to design ligand analogs were motivated by their potential antibiotic activity. However, riboswitches are ideally suited as tools for gene therapy, enabling precise control of gene ex-pression without the need of potentially immunogenic regulatory proteins. Developing synthetic RNA switches starting from natural riboswitches will require engineering both, the ligand and the RNA sequence in order to achieve full orthogonality i.e., sensitivity to the designed small molecule modulator, but not to the natural ligand. We present the structure-based design of a drug-like small molecule ligand of the thiamine pyrophosphate (TPP) aptamer, BI-5232. BI-5232 is structurally highly diverse from the natural ligand TPP but rivals its binding affinity (KD = 1.0 nM). Importantly, in our design the pyrophosphate of TPP was replaced by an uncharged heterocycle that interacts with the PP helix in an unprecedented way, as revealed by Molecular Dynamics simulations. Subsequently, we altered the aptamer sequence to drastically reduce its affinity to TPP while retaining binding properties for our designed ligand. Based on the developed orthogonal small molecule/RNA aptamer interaction we finally constructed orthogonal ribozyme-based ON- and OFF-switches of gene expression in human cell lines. Such systems are valuable additions to the synthetic toolbox for conditionally controlling gene expression with potential applications in next-generation gene therapies.

synthetic biology↗

bioRxiv2023

Structural basis of the mechanism and inhibition of a human ceramide synthase

Ceramides are bioactive sphingolipids that play pivotal roles in regulating cellular metabolism. Ceramides and dihydroceramides are synthesized by a family of six ceramide synthase enzymes (CerS), each with distinct specificity for the acyl-CoA substrate. Importantly, the acyl chain length plays a key role in determining the physiological function of ceramides, as well as their role in metabolic disease. Ceramide with an acyl chain length of 16 carbons (C16 ceramide) has been implicated in obesity, insulin resistance and liver disease, and the C16 ceramide-synthesizing CerS6 is regarded as an attractive drug target for obesity-associated disease. Despite their importance, the molecular mechanism underlying ceramide synthesis by CerS enzymes remains poorly understood. Here, we report cryo-electron microscopy structures of human CerS6, capturing covalent intermediate and product-bound states. These structures, together with biochemical characterization using intact protein and small molecule mass spectrometry, reveal that CerS catalysis proceeds via a ping-pong reaction mechanism involving a covalent acyl-enzyme intermediate. Notably, the product-bound structure was obtained upon reaction with the mycotoxin fumonisin B1, providing new insights into its inhibition of CerS. These results provide a framework for understanding the mechanisms of CerS function, selectivity, and inhibition, and open new directions for future drug discovery targeting the ceramide and sphingolipid pathways.

biochemistry↗