Biology subjects

Seebohm, G.

Publications and source records attributed to Seebohm, G..

9 recordsLinked to original sources

bioRxiv2026

A sequence variation between two orthologues alters functional expression of the potassium channel Kesv of Ectocarpus siliculosus virus

The potassium channel Kesv encoded by the Ectocarpus siliculosus virus (Kesv 1) differs by seven amino acid residues from its host-derived homolog (Kesv 2), resulting from lysogenic integration. When expressed in Xenopus laevis oocytes, Kesv 1 displayed significantly higher ion conductance and functional expression than Kesv 2, as demonstrated by GFP fluorescence and voltage clamp measurements. This study provides the first structural and functional analysis of Kesv 2, uncovering key differences between the original and host-derived variant. The systematic residue substitutions - based on location- from Kesv 2 to the corresponding residues in Kesv 1 illustrated that two amino acid exchanges in close proximity to the pore region (Q61H and T66A), albeit not individually but in combination, significantly resulted in a loss-of-function phenotype in Kesv 1. AlphaFold predictions and subsequent molecular dynamics simulations did not reveal significant differences between Kesv 1 and Kesv 2 structural models, suggesting that the loss of function cannot be attributed to differences at the structural level. Instead, a reduced surface expression of Kesv 2, caused by the sequence modulations in the brown algal host, appears more plausible. Notably, the pharmacological profiling with Linopirdine and Sotalol highlights differences in drug sensitivity, establishing these minimalist channels (core channel structure without regulatory domains) as tractable models for dissecting novel fundamental principles of ion channel function and drug interaction, while highlighting key differences from more complex channel systems. Significance StatementPotassium channels are essential for cellular excitability, yet their large size and structural complexity limit our understanding of the core features underlying channel function. Here, we identified and established an orthologous model to compare the effects of evolutionarily acquired mutations in two voltage-sensing potassium channels-the viral potassium channel from Ectocarpus siliculosus virus (Kesv 1) and its host-homolog derivative (Kesv 2) as simplified model systems for understanding ion channel physiology and host-viral interactions. We provide the first functional characterization of Kesv 2 in Xenopus laevis oocytes using two-electrode voltage-clamp and site-directed mutagenesis, revealing that, despite sharing an identical SVGYG selectivity-filter motif and differing by only 7 residues, they exhibit distinct ion-conduction properties.

pharmacology and toxicology↗

bioRxiv2024

TMPRSS6 cleaves KCNE1 and causes arrhythmias in iron overload disease

Iron storage disease is associated with cardiovascular manifestations, including various forms of cardiac arrhythmias of unknown origin. In this study, cardiac arrhythmias associated with iron overload were investigated in human iPSC-derived cardiomyocytes (hiPSC-CM) and hiPSC-derived sinus node-like pacemaker cells. Among other effects, iron overload leads to an increase in the plasma membrane-anchored protease TMPRSS6. TMPRSS6 cleaves the auxiliary subunit KCNE1 N-terminally and thus modulates the function of both the IKs (KCNQ1/KCNE1 current) and the If (HCN4/KCNE1) ion channels. Furthermore, TMPRSS6 induces a reduction of electric field potential (EFP) count and increased duration in hiPSC-derived ventricular-like cells and in hiPSC-derived pacemaker-like cells. In accordance with these in vitro generated results, TMPRSS6-mediated interactions show pro-arrhythmic effects in silico. Therefore, the TMPRSS6 - KCNE1-KCNQ1 and TMPRSS6 - KCNE1-HCN4 cascades may represent new clinically relevant pro-arrhythmic mechanisms in iron overload diseases.

physiology↗

bioRxiv2024

Decreased ATP synthase activity is linked to altered spatiotemporal organisation of ATP Synthase in a cellular cardiomyocyte senescent model

Heart disease is the leading cause of death in the elderly population and the heart is a highly energy-consuming tissue. Aging-related heart failure is often driven by energy depletion in cardiomyocytes (CM), which rely on their abundant, cristae-dense mitochondria for ATP production. ATP synthase, localized along the cristae rims, plays a critical role in energy conversion, but the connection between its organization and function remains unclear. Here, we explored the spatiotemporal organization of ATP synthase in senescent CM at the level of individual complexes. Using single-molecule localization and tracking microscopy, we observed reduced enzyme mobility within the cristae, coinciding with decreased ATP synthase activity, despite a stable resting mitochondrial membrane potential. This reduction in activity was independent of changes in ATP synthase expression or dimerization. Electron tomography revealed an increased prevalence of curved inner membranes and fenestrated cristae in senescent CM, explaining the reduced enzyme mobility. Senescent CM displayed irregular autonomous and paced beating patterns. These abnormalities suggest that impaired cardiac function is directly driven by disrupted energy metabolism, rooted in the suboptimal organization and function of ATP synthase in altered cristae.

cell biology↗

bioRxiv2024

Locityper: targeted genotyping of complex polymorphic genes

The human genome contains numerous structurally-variable polymorphic loci, including several hundred disease-associated genes, almost inaccessible for accurate variant calling. Here we present Locityper, a tool capable of genotyping such challenging genes using short and long-read whole genome sequencing. For each target, Locityper recruits and aligns reads to locus haplotypes, for instance extracted from a pangenome, and finds the likeliest haplotype pair by optimizing read alignment, insert size and read depth profiles. Locityper accurately genotypes up to 194 of 256 challenging medically relevant loci (95% haplotypes at QV33), an 8.8-fold gain compared to 22 genes achieved with standard variant calling pipelines. Furthermore, Locityper provides access to hyperpolymorphic HLA genes and other gene families, including KIR, MUC and FCGR. With its low running time of 1h10m per sample at 8 threads, Locityper is scalable to biobank-sized cohorts, enabling association studies for previously intractable disease-relevant genes.

bioinformatics↗

bioRxiv2024

Tagging of Exo70 at the N-terminus compromises its assembly with the exocyst complex and changes its spatiotemporal behavior at the plasma membrane

The vesicle-tethering exocyst complex is a key regulator of cell polarity. The subunit Exo70 is required for the targeting of the exocyst complex to the plasma membrane. While the N-terminus of Exo70 is important for its regulation by GTPases, the C-terminus binds to PI(4,5)P2 and Arp2/3. Here, we compare N- and C-terminal tagged Exo70 with respect to subcellular localization, dynamics and function in cell membrane expansion. Using high-resolution imaging, we determined the spatial distribution and dynamics in different sub-compartments of un-polarized and polarized cells. With lattice light-sheet microscopy, we show that HaloTag-Exo70, but not Exo70-HaloTag, promotes the outgrowth of filopodia-like structures from the axon of hippocampal neurons. Fluorescence lifetime imaging of sfGFP-Exo70 and molecular modeling results suggest that the assembly of sfGFP-Exo70 with the exocyst complex is reduced. This is supported by single particle tracking data showing higher mobility of N- than C-terminal tagged Exo70 at the plasma membrane. The distinct spatiotemporal properties of N-terminal tagged Exo70 were correlated with pronounced filopodia formation in unpolarized cells and neurons, a process that is less reliant on exocyst complex formation. We therefore propose that N-terminal tagging of Exo70 shifts its activity to processes that are less exocyst-dependent. Why it mattersIn the life sciences, the high-resolution visualization of processes in living cells is of great interest. To tag proteins, they are fused with fluorescent proteins, usually at the N- or C-terminus of the amino acid sequence. We show here that the position of the tag alters the function and interaction of Exo70, a polypeptide involved in vesicle fusion, but also in membrane bending and expansion. Using state-of-the-art microscopic techniques, single particle localization and tracking, fluorescence lifetime imaging microscopy and co-localization in combination with modeling, we conclude that N-terminal tagging of Exo70 impairs its assembly with the exocyst complex and instead promotes the interaction of free Exo70 with the actin skeleton, which favors controlled membrane expansion into filipodia.

biophysics↗

bioRxiv2024

Mdivi-1 affects neuronal activity by inhibition of Complex I and respiratory supercomplex assembly

Several human diseases, including cancer and neurodegeneration, are associated with excessive mitochondrial fragmentation. In this context, mitochondrial division inhibitor (Mdivi-1) has been tested as a therapeutic to block the fission-related protein dynamin-like protein-1 (Drp1). Recent studies suggest that Mdivi-1 interferes with mitochondrial bioenergetics. Here we show that the molecular mechanism of Mdivi-1 is based on inhibition of complex I at the IQ site. This leads to the destabilization of complex I, impairs the assembly of N- and Q-respirasomes and is associated with increased ROS production. The result is a reduced efficiency of ATP generation. Second, the calcium homeostasis of cells is impaired, which severely affects the electrical activity of neurons. Given the results presented here, a potential therapeutic application of Mdivi-1 is challenging because of its impact on synaptic activity. Similar to the Complex I inhibitor rotenone, Mdivi-1 may lead to neurodegenerative effects in the long term. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=114 SRC="FIGDIR/small/577160v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@1bffc82org.highwire.dtl.DTLVardef@15ae3b5org.highwire.dtl.DTLVardef@1ba3a5org.highwire.dtl.DTLVardef@94cfc0_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIMdivi-1 inhibits respiratory complex I at the IQ-site C_LIO_LIInhibition destabilizes complex I and reduces supercomplex formation C_LIO_LIMitochondrial ATP levels decrease C_LIO_LICa2+ metabolism is affected C_LIO_LINeuronal activity is compromised C_LI

cell biology↗

bioRxiv2021

An Activator Locks Kv7.1 Channels Open by Electro-Mechanical Uncoupling and Allosterically Modulates its Pore with similarity to phosphatidylinositol-4,5-bisphosphat

Loss-of-function mutations in Kv7.1 often lead to long QT syndrome (LQTS), a cardiac repolarization disorder associated with increased risk of arrhythmia and subsequent sudden cardiac death. The discovery of agonistic IKs modulators may offer a new potential strategy in pharmacological treatment of this disorder. The benzodiazepine (R)-L3 potently activates Kv7.1 channels and shortens action potential duration, thus may represent a starting point for drug development. However, the molecular mechanisms underlying modulation by (R)-L3 are still unknown. By combining alanine scanning mutagenesis, non-canonical amino acid incorporation, voltage-clamp electrophysiology and fluorometry, and in silico protein modelling, we showed that (R)-L3 not only stimulates currents by allosteric modulation of the pore domain but also alters the kinetics independently from the pore domain effects. We identified novel (R)-L3-interacting key residues in the lower S4-segment of Kv7.1 and observed an uncoupling of the outer S4 segment with the inner S5, S6 and selectivity filter segments. Summarizing, we provide structural and functional evidence for two independent Kv7.1 activating mechanisms by a single modulator.

biophysics↗

bioRxiv2019

Two-stage electro-mechanical coupling of a Kv channel in voltage-dependent activation

In voltage-gated potassium (KV) channels, the voltage-sensing domain (VSD) undergoes sequential activation from the resting state to the intermediate state and activated state to trigger pore opening via electro-mechanical (E-M) coupling. However, the spatial and temporal details underlying E-M coupling remain elusive. Here, we leverage KV7.1s unique two open states associated with the VSD adopting the intermediate and activated conformations to report a two-stage E-M coupling mechanism in voltage-dependent gating of KV7.1 as triggered by VSD activations to the intermediate and then activated state. When the S4 segment transitions to the intermediate state, the hand-like C-terminus of the VSD-pore linker (S4-S5L) interacts with the pore in the same subunit. When S4 then proceeds on to the fully-activated state, the elbow-like hinge between S4 and S4-S5L engages with the pore to activate conductance. This two-stage \"hand-and-elbow\" gating mechanism elucidates distinct tissue-specific modulations, pharmacology, and disease pathogenesis of KV7.1, and likely applies to numerous KV channels.

biophysics↗

bioRxiv2018

Bioelectric-calcineurin signaling module regulates allometric growth and size of the zebrafish fin

The establishment of relative size of organs and structures is paramount for attaining final form and function of an organism. Importantly, variation in the proportions of structures frequently underlies adaptive change in morphology in evolution and maybe a common mechanism underlying selection. However, the mechanism by which growth is integrated within tissues during development to achieve proper proportionality is poorly understood. We have shown that signaling by potassium channels mediates coordinated size regulation in zebrafish fins. Recently, calcineurin inhibitors were shown to elicit changes in zebrafish fin allometry as well. Here, we identify the potassium channel kcnk5b as a key player in integrating calcineurins growth effects, in part through regulation of the cytoplasmic C-terminus of the channel. We propose that the interaction between Kcnk5b and calcineurin acts as a signaling node to regulate allometric growth. Importantly, we find that this regulation is epistatic to inherent mechanisms instructing overall size as inhibition of calcineurin is able to bypass genetic instruction of size as seen in sof and wild-type fins, however, it is not sufficient to re-specify positional memory of size of the fin. These findings integrate classic signaling mediators such as calcineurin with ion channel function in the regulation of size and proportion during growth.

developmental biology↗