Biology subjects

Timmermann, V.

Publications and source records attributed to Timmermann, V..

5 recordsLinked to original sources

bioRxiv2026

An ER Retrieval-and-Release System Reveals Ligand-Independent Basal Signaling by Cell Surface TCRs

The T cell receptor (TCR) machinery comprises the ligand-binding TCR{beta} and the CD3 signaling dimers. Individual subunits are synthesized in the endoplasmic reticulum (ER) and only the fully assembled TCRs reach the cell surface. We engineered a system to retained CD3{varepsilon} is in the ER. This allowed only partial TCR assembly, while continuous retrieval of CD3{varepsilon} from the Golgi back to the ER enabled complete assembly. Synchronous TCR release by biotin addition caused a transient increase in surface TCR abundance that gradually returned to steady-state levels. Mathematical modeling revealed that TCR levels were controlled by feedback mechanisms. Notably, surface-localized, but not ER-localized, TCRs spontaneously generated ligand-independent basal signaling. Phosphoproteomic analyses revealed that this signal is similar, but not identical, to ligand-induced TCR activation signals, with distinct phosphorylation patterns already evident at the CD3 subunits. Our findings establish the TCR retrieval-and-release system as a tool to investigate ligand-independent basal TCR signaling.

immunology↗

bioRxiv2026

Human NHE1 binds full-length calcineurin with high affinity and inhibits substrate dephosphorylation

Calcineurin (Cn) interacts with the Na+/H+-exchanger NHE1 through its calcineurin-binding domain (NHE1-CnBD). How activation of full-length Cn influences this interaction and its functional consequences has remained unclear. Here, we quantified the interaction between full-length human Cn and NHE1-CnBD in distinct activation states using fluorescence anisotropy and quantitative size-exclusion chromatography. Ca2+/calmodulin activation increased Cn affinity for NHE1-CnBD from submicromolar to tens of nanomolar affinity and stabilized the complex. NHE1-CnBD outcompeted the immunosuppressive cyclosporin A/cyclophilin A complex for Cn binding and selectively inhibited dephosphorylation of a phosphopeptide substrate while enhancing hydrolysis of p-nitrophenyl phosphate. These findings identify NHE1 as a high-affinity, substrate-competitive Cn regulator that blocks substrate recognition rather than catalysis, providing a mechanistic framework for reciprocal regulation between Cn and NHE1.

biochemistry↗

bioRxiv2026

Channelrhodopsin Ion Selectivity Determines Mechanisms and Efficacy of Optogenetic Defibrillation in Human Atria and Ventricles

Optogenetic defibrillation uses light-gated ion channels to terminate cardiac arrhythmias through targeted illumination. Previous studies assessed the feasibility of using either cation (e.g. ChR2) or anion (e.g. GtACR1) non-selective channels, both of which depolarise resting cardiomyocytes upon photoactivation. In contrast, recently identified light-gated K+-channels (e.g. WiChR) suppress cardiomyocyte activity while maintaining the membrane potential near its resting state. Here, we use biophysically detailed simulations to compare the defibrillation potential of ChR2, GtACR1, and WiChR. Single-cell simulations show that activation of ChR2 and GtACR1 markedly increase diastolic intracellular Ca2+ concentration (by 42.6% and 52.6%, respectively), whereas WiChR induces only minimal changes (4.0% increase), suggesting a lower pro-arrhythmogenic risk. WiChR activation, however, slightly increases intracellular Na+ levels (by 15.1% compared to 0.1% and 3.4% for ChR2 and GtACR), consistent with the residual Na+ permeability of all currently available K+-selective channelrhodopsins. Simulations of human ventricles and atria demonstrate that GtACR1 most effectively terminates re-entrant arrhythmias at low light intensities, while WiChR achieves comparable efficacy at light levels [≥]5 mW/mm2. Complementary tissue-scale simulations reveal that defibrillation is either based on depolarisation within the excitable gap, followed by fast Na+ channel inactivation (depolarising variants ChR2 and GtACR1), or based on a reduction in membrane resistance supporting arrhythmia termination at sufficiently high light levels (large-conductance ion channels GtACR1 and WiChR). Overall, our findings identify channelrhodopsin ion selectivity as a key determinant of both arrhythmia termination success and mechanisms underlying defibrillation. Key points summaryO_LIWe use computational simulations to compare non-selective cation (ChR2), anion (GtACR1), and K+-selective channelrhodopsins (WiChR) for optogenetic termination of re-entrant arrhythmia. C_LIO_LISingle-cardiomyocyte simulations suggest that ChR2 and GtACR1 activation can cause progressive accumulation of intracellular Ca2+, which is minimised when using WiChR. C_LIO_LISimulations of human left ventricles and atria indicate that GtACR1 is most effective in terminating re-entrant arrhythmia at low light intensities, while WiChR becomes similarly effective at higher intensities. C_LIO_LITissue-scale simulations indicate distinct defibrillation mechanisms: Excitable gap extinction by de-novo action potential initiation followed by inactivation of fast Na+ channels for depolarising channelrhodopsins (ChR2, GtACR1), and reduction in membrane resistance for the large-conductance channels (GtACR1, WiChR), effectively clamping the membrane potential at each channels reversal potential at high light levels. C_LI

physiology↗

bioRxiv2022

Drought effects of annual and long-term temperature and precipitation on mortality risk for 9 common European tree species

Risk factors for natural tree mortality in managed forests, excluding wind and snow induced breakage, fires and thinning, can be difficult to identify due to correlated confounders of long- and short-term weather patterns with tree age. This study quantified the association of annual and long-term 30-year average temperature and precipitation effects on individual tree death across Europe from 2011 to 2020 for European beech, sessile and pedunculate oak, silver birch, black pine, Austrian oak, Scots pine, European hornbeam, and Norway spruce. For each species, logistic regression approaches for predicting annual mortality evaluated the influence of age, exposition and weather effects on individual tree death, while accounting for multi-collinearity of risk factors. For all species except sessile oak, higher 30-year-temperature averages were associated with higher odds of tree mortality. Effect size of other risk factors varied among species, with similar weather associations between Austrian and sessile oak on the one hand, and Scots pine, Norway spruce and pedunculate oak on the other hand. In particular, warmer winters reduced mortality for silver birch, sessile and Austrian oaks, while having the opposite association for the other species. Sessile oak was most robust against drought effects and could serve as an important tree species under climate change scenarios.

plant biology↗

bioRxiv2021

European-wide forest monitoring substantiate the neccessity for a joint conservation strategy to rescue European ash species (Fraxinus spp.)

European ash (Fraxinus excelsior) and narrow-leafed ash (F. angustifolia) are keystone forest tree species in Europe with a broad ecological amplitude and significant economic importance. Besides global warming both species are currently under significant thread by an invasive fungal pathogen that has been progressively spreading throughout the continent for almost three decades. Ash dieback caused by the invasive ascomycete Hymenoscyphus fraxineus is capable of damaging ash trees of all age classes and often leads to the ultimate death of a tree after years of progressively developing crown defoliation. While studies at national and regional level already suggested rapid decline of ash populations as a result of ash dieback, a comprehensive survey at European level with harmonized crown assessment data across countries could shed more light into the population decline from a pan-European perspective and could also pave the way for a new conservation strategy beyond national boarders. Here, we present data from the ICP Forests Level I crown condition monitoring including 27 countries, covering the timespan from 1987-2020. In total, 407 survey plots randomly distributed across these countries were analyzed resulting in >36,000 individual observations. We found a substantial increase in defoliation and mortality over time indicating that crown defoliation has almost doubled during the last three decades. Hotspots of mortality are currently situated in southern Scandinavia and north-eastern Europe, well corresponding to the fact that the disease spread fast from north-east to north-west. Overall survival probability after nearly 30 years of infection has already reached a critical value of 0.51, but with large differences among regions (0.00-0.907). Both a Cox proportional hazard model as well as an Aalen additive regression model strongly suggest that survival of ash is significantly lower in locations with excessive water regime and which experienced more extreme precipitation events during the last two decades. Our results underpin the neccessity for fast governmental acting and joint rescue efforts beyond national boarders since overall mean defoliation will likely reach 50% as early as 2030 as suggested by time series forecasting. We strongly recommend to develop a pan-European conservation strategy before the decline will reach its tipping point resulting into non-reversible loss of diversity in the European forest landscape.

ecology↗