Biology subjects

Witte, G.

Publications and source records attributed to Witte, G..

4 recordsLinked to original sources

bioRxiv2026

The vacuolar tauopathy-associated mutation D395G confers redox sensitivity to p97/VCP

The multifunctional AAA+ ATPase p97/VCP is a pivotal regulator of cellular proteostasis, extracting polyubiquitinated substrates from protein complexes or organelle membranes for proteasomal degradation. Mutations in p97 are linked to a broad spectrum of neurodegenerative disorders, including multisystem proteinopathy and amyotrophic lateral sclerosis. Here, we provide insights into the basis of dysfunction in p97D395G, implicated in vacuolar tauopathy, using an integrated structural approach. The mutation destabilizes the interaction network in the transient ADP.Pi state previously identified in p97WT and alters the dynamics of the linker between the tandem ATPase domains, resulting in decreased ATPase activity. We further demonstrate that the D395G mutation sensitizes p97 to oxidative stress by enhancing C522 oxidation, thereby perturbing nucleotide binding in D2, and define the functional basis of this oxidative inactivation of p97. These findings reveal redox control as a key regulatory layer of the p97 ATPase cycle and provide a mechanistic framework for how oxidative stress contributes to p97-associated neurodegeneration.

molecular biology↗

bioRxiv2025

Functional and intricate interaction network connecting Helicobacter pylori Cag Type 4 Secretion System surface proteins with outer membrane proteins HopQ and HopZ

The Helicobacter pylori cag pathogenicity island (cagPAI) encodes a complex type IV secretion system (CagT4SS) which is an important virulence factor of H. pylori. Recently, structural detail on the CagT4SS has been substantially improved by cryo-EM. However, important structural and functional information, in particular on protein interactions between T4SS surface proteins, and of T4SS surface proteins with other proteins, is missing. In the present study, we followed the hypothesis that H. pylori T4SS external proteins may form a surface protein assembly, together with other, non-CagT4SS proteins, which may also be essential for T4SS function. Using interaction screens of H. pylori CagT4SS surface proteins, followed by biochemical and functional characterization, we have enhanced the knowledge on protein-protein interactions of CagT4SS extracellular proteins. This also includes newly identified interactions of CagT4SS surface proteins, for instance the VirB2 homolog CagC, the VirB5 homolog CagL and the surface protein CagN of unknown function, with outer membrane proteins HopQ and HopZ. We have further identified and quantitated direct interactions of T4SS surface proteins with outer membrane proteins HopZ and HopQ, which play a role in T4SS functions, and of both HopZ and HopQ with themselves and with host cell factors CEACAM and integrin. Furthermore, we determined an influence of pH on interactions between HopQ/HopZ and CagT4SS components. Utilizing protein tag insertions in H. pylori, we detected surface-exposed association of HopQ and HopZ with T4SS components on bacteria without or with (for HopQ) human gastric epithelial cells. Functionally antagonistic roles of HopQ and HopZ were uncovered in T4SS-dependent early pro- inflammatory human epithelial cell activation. In summary, we identified a network of interactions between H. pylori outer membrane proteins and CagT4SS surface proteins and characterized them as functionally important for transport processes. This will help to refine structural and functional details regarding surface-exposed proteins of the CagT4SS.

microbiology↗

bioRxiv2024

Trafficking of the Telomerase RNA using a Novel Genetic Approach

Telomeres are specialized nucleoprotein structures situated at eukaryotic chromosome ends, vital for preserving genetic information during cell replication. Telomerase, a holoenzyme composed of telomerase reverse transcriptase and an RNA template component (TER), is responsible for elongating telomeric DNA. The intracellular trafficking of the telomerase RNA varies, either staying in the nucleus or exiting to the cytoplasm, depending on the organism. For example, in Saccharomyces cerevisiae, the RNA template is exported to the cytoplasm, whereas in mammalian cells and protozoa, it remains within the nucleus. Aspergillus nidulans, a filamentous fungus, offers an outstanding model for investigating telomeres and telomerase due to its characterized telomerase components, exceptionally short and tightly regulated telomeres, and innovative heterokaryon rescue technique. To determine the pathway of telomerase RNA trafficking in A. nidulans, we leveraged its unique capabilities to exist in both uni- and multi-nucleate states within a heterokaryon. This involved creating a TER knockout A. nidulans strain (TER{Delta}) and examining the resulting colonies for signs of heterokaryon formation. Heterokaryons would imply the export of TER from one nucleus and its import into a TER{Delta} nucleus. Interestingly, the TER{Delta} strain consistently failed to produce heterokaryons, instead giving rise to diploid colonies. This surprising finding strongly implies that telomerase assembly predominantly takes place within the nucleus of A. nidulans, distinguishing it from the biogenesis and trafficking pattern observed in yeast.

molecular biology↗

bioRxiv2019

c-di-AMP hydrolysis by a novel type of phosphodiesterase promotes differentiation of multicellular bacteria

Antibiotic-producing Streptomyces use the diadenylate cyclase DisA to synthesize the nucleotide second messenger c-di-AMP but the mechanism for terminating c-di-AMP signaling and the proteins that bind the molecule to effect signal transduction are unknown. Here, we identify the AtaC protein as a new type of c-di-AMP-specific phosphodiesterase that is also conserved in pathogens such as Streptococcus pneumoniae and Mycobacterium tuberculosis. AtaC is monomeric in solution and binds Mn2+ to specifically hydrolyze c-di-AMP to AMP via the intermediate 5-pApA. As an effector of c-di-AMP signaling, we characterize the RCK-domain protein CpeA as the first c-di-AMP-binding protein to be identified in Streptomyces. CpeA interacts with the predicted cation / proton antiporter, CpeB, linking c-di-AMP signaling to ion homeostasis in actinobacteria. Hydrolysis of c-di-AMP is critical for normal growth and differentiation in Streptomyces, connecting osmotic stress to development. Thus, we present the discovery of two novel components of c-di-AMP signaling in bacteria and show that precise control of this second messenger is essential for osmoregulation and coordinated development in Streptomyces.

microbiology↗