Biology subjects

Franta, Z.

Publications and source records attributed to Franta, Z..

4 recordsLinked to original sources

bioRxiv2026

Host-derived lipids license proliferation of sterol-auxotrophic tick cells and promote flavivirus output

Sterol molecules play indispensable roles in the biology of cells and organisms. Yet, arthropods, including ticks, lack the capacity for de novo sterol biosynthesis and must rely on exogenous sources. How these organisms sense and utilise exogenous lipids at the cellular level remains poorly understood. Here, we show that host cholesterol and linoleic acid act as essential external signals that license proliferation of Ixodes ricinus tick cells. In lipid-depleted conditions, cells fail to proliferate despite retaining intracellular cholesterol, indicating that exogenous lipids function as regulatory cues rather than merely structural components. We further demonstrate that tick cells exhibit a non-canonical intracellular distribution of cholesterol, with predominant accumulation in lysosome-associated compartments, and that lipid availability induces a coordinated transcriptional program involving lipid uptake and trafficking machinery. Importantly, we find that limiting host lipid availability significantly reduces extracellular RNA output of tick-borne encephalitis virus (TBEV) from infected tick cells, indicating that viral production is affected by the metabolic state of the host cell. Together, our findings establish host-derived lipids as key regulators of cellular state in a sterol-auxotrophic organism and identify lipid availability as a determinant of flavivirus output. This work provides a conceptual framework linking nutrient sensing, cell proliferation, and vector-pathogen interactions.

microbiology↗

bioRxiv2025

In situ protein crystallography: a single-crystal electron diffraction pipeline for structure determination inside living cells.

Intracellular crystallization is an emerging approach in structural biology that bypasses the need for protein purification. An InCellCryst pipeline was recently established for structure determination by serial X-ray crystallography. Serial crystallography requires the exposure of tens of thousands of cells containing intracellular crystals, precluding high-resolution structural studies on proteins with low numbers of crystals. To overcome this limitation, we combined the InCellCryst approach with the advantages of 3D electron diffraction and established the new IncellED method. Using microcrystals of the HEX-1 protein from Magnaporthe grisea, grown inside High Five insect cells, we demonstrate that electron diffraction data collected from a single crystal yields a high-resolution structure at 1.9 [A] resolution, comparable to 1.8 [A] achieved by serial X-ray crystallography. The IncellED methodology opens structure determination for proteins that crystallize with low efficiency and use widely available electron cryo-microscope infrastructure, paving the way for intracellular macromolecular electron crystallography at high resolution.

biophysics↗

bioRxiv2022

Mechanistic insight into the ATP hydrolysis cycle of tick-borne encephalitis virus helicase

Helicase domain of nonstructural protein 3 (NS3H) unwinds double-stranded RNA replication intermediate during flavivirus life cycle in ATP-dependent manner. While the helicases mechanism of Dengue and Zika viruses has been extensively studied, little is known about helicase activity of the tick-borne encephalitis virus NS3. In the current study, we demonstrated that ATP hydrolysis cycle of NS3H is strongly stimulated by ssRNA but not ssDNA, suggesting that NS3H is an RNA-specific helicase. However, ssDNA binding inhibits ATPase activity in a non-competitive manner. We also captured several structural snapshots of key ATP hydrolysis stages. An intermediate, in which the inorganic phosphate (Pi) and ADP resulted from ATP hydrolysis and remain trapped inside the ATPase site, suggests that Pi release is the rate-limiting step and is accelerated by RNA binding and/or translocation. Based on these structures, we modeled NS3H-ssRNA and -ssDNA binding and performed MD simulations. Our model suggests that NS3H-ssRNA binding triggers conformational changes, revealing the coupling between helicase and ATPase activities. The structural models revealed that ssDNA inhibition may occur via non-specific ssDNA binding to several positively charged surface patches which in turn causes repositioning of ATP molecule within the ATPase site.

biochemistry↗

bioRxiv2019

Bicistronic expression and differential localization of proteins in insect cells and Drosophila suzukii using picornaviral 2A peptides

Polycistronic expression systems in insects can be used for applications such as recombinant protein production in cells, enhanced transgenesis methods, and the development of novel pest-control strategies based on the sterile insect technique (SIT). Here we tested the performance of four picornaviral 2A self-cleaving peptides (TaV-2A, DrosCV-2A, FMDV 2A1/31 and FMDV 2A1/32) for the co-expression and differential subcellular targeting of two fluorescent marker proteins in cell lines (Anastrepha suspensa AsE01 and Drosophila melanogaster S2 cells) and in vivo in the pest insect Drosophila suzukii. We found that all four 2A peptides showed comparable activity in cell lines, leading to the production of independent upstream and downstream proteins that were directed to the nucleus or membrane by a C-terminal nuclear localization signal (NLS) on the upstream protein and a poly-lysine/CAAX membrane anchor on the downstream protein. Two of the 2A peptides were inserted into piggyBac constructs to create transgenic D. suzukii strains, confirming efficient ribosomal skipping in vivo. Interestingly, we found that the EGFP-CAAX protein was distributed homogeneously in the membrane whereas the DsRed-CAAX protein formed clumps and aggregates that induced extensive membrane blebbing. Accordingly, only flies expressing the EGFP-CAAX protein could be bred to homozygosity whereas the DsRed-CAAX construct was lethal in the homozygous state. Our results therefore demonstrate that four different 2A constructs and two novel targeting motifs are functional in D. suzukii, and that DsRed-CAAX shows dosage-dependent lethality. These molecular elements could be further used to improve expression systems in insects and generate novel pest control strains.\n\nHighlightsO_LIFour picornaviral 2A peptides have been studied for their self-cleaving ability in cell lines and in vivo in the pest insect Drosophila suzukii.\nC_LIO_LIAll tested 2A peptides showed comparable activity that resulted in the production of independent upstream and downstream proteins.\nC_LIO_LIThe proteins co-expressed by 2A peptides were either directed to the cell nucleus by a C-terminal nuclear localization signal (NLS), or to the cell membrane by a poly-lysine/CAAX membrane anchor.\nC_LIO_LIThe combination of optimized membrane localization signals fused to DsRed generated an intrinsically lethal phenotype, which can be used to develop novel pest control strains.\nC_LI

bioengineering↗