Biology subjects

Sattler, C.

Publications and source records attributed to Sattler, C..

6 recordsLinked to original sources

bioRxiv2024

Subunit-specific conductance of single HCN pacemaker channels at femtosiemens resolution

Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are tetramers that generate rhythmic electrical activity in neuronal and cardiac pacemaker cells 1. The channels are activated by hyperpolarisation of the membrane voltage and additionally tuned by the second messenger cAMP at sympathetic stimulation. There are four mammalian isoforms, HCN1-4 2-4. The single-channel conductance,{gamma} , of HCN channels remains debated, with conflicting results ranging from near 1.5 pS for HCN2 5,6 to tens of pS for HCN1 7, HCN2 7 and HCN4 7,8, though the pore structure, viewed to determine the conductance 9,10, is either identical or highly conserved. To resolve this controversy, we analyzed all four mouse isoforms mHCN1-4 at femtosiemens resolution. We show that mHCN1, mHCN3 and mHCN4 also generate small conductance values, even smaller than that of mHCN2 with the sequence{gamma} mHCN2=1.54 pS >{gamma} mHCN1=0.84 pS >{gamma} mHCN3=0.54 pS {asymp}{gamma} mHCN4=0.51 pS. As shown by systematic mutagenesis and molecular dynamic simulations, the differences in the conductance are neither generated by the selectivity filter nor the inner gate 9, but by defined negative charges in the outer channel vestibule increasing cation occupation. In line with these results, heteromers of mHCN2 with either mHCN1, mHCN3 or mHCN4 lead to graded single-channel currents in-between those of the respective homomeric channels. Our approach at femtosiemens resolution provides insight into the function of recombinant and native HCN channels at the level of single subunits and is thus promising for the development of subunit-specific drugs acting on these clinically highly relevant channels 11.

physiology↗

bioRxiv2024

A-Islands: A plant dataset for biodiversity research and species monitoring on Australian islands

Australias coastline is fringed by more than 8,000 continental islands. These islands feature a diverse array of landforms, rock and soil types and geological origins. Some of these islands are among the least invaded, most pristine habitats in Australia and support high plant diversity. Here, we present a new Australia-wide curated dataset for plant species occurrences on islands. Combining information from 1,349 species lists and floras, A-Islands includes data on >6,500 plant species from 844 islands ranging in size from 18 m2 to 4,400 km2, exhibiting different degrees of isolation from the mainland, and spanning all major Australian climate zones. Of these, 251 islands have been repeatedly sampled up to 11 times making it possible to investigate temporal compositional change. A-Islands is open access and will be continuously updated. Its simple data structure consisting of three comma separated files allows easy integration with other Australian and global plant-occurrence databases and can serve as a repository for island research in Australia. Knowing which species occur on Australia's islands will provide opportunities for future research, including studying changes in biodiversity and species-turnover within and among archipelagos, tests of classical island biogeography theory and as a baseline for ecological monitoring and conservation.

ecology↗

bioRxiv2024

Physiological barriers for glucose utilization in Methanosarcina acetivorans

Methanogenesis is a key aspect of anaerobic biomass degradation, and thus of global importance. While methanogenic archaea (methanogens) are ubiquitous in anaerobic habitats, the range of substrates they utilize is very limited. Most methanogens are able to grow chemolithotrophically with H2+CO2, some clades can utilize methylated compounds and/or acetate as well. Organotrophic compounds like amino acids, lipids, nucleotides, or carbohydrates, are not known to support growth of methanogens. This inability to utilize "upstream" intermediates of anaerobic biomass degradation is remarkable considering the presence of cellular metabolism that such intermediates could feed into. Here, we addressed the question why the model methanogen Methanosarcina acetivorans, despite its gluconeogenic and glycolytic capacity, is unable to utilize glucose for methanogenesis and growth. Complementing heterologously with a glucose uptake facilitator allowed a recombinant M. acetivorans strain to convert glucose to methane at a low rate. However, growth with glucose was not observed, neither as energy source nor as carbon source. Instead, methylotrophic growth of the transgenic strain was impaired in a glucose-dependent fashion, which was aggravated when also glucokinase was heterologuously produced. Glucose-dependent growth inhibition coincided with a significant - and microscopically visible - accumulation of intracellular carbohydrate. Since the glucose-utilizing trait is rapidly lost during methylotrophic growth, accumulating growth-inhibiting metabolites probably makes methanogenic and glycolytic catabolism incompatible. Thus, extensive efforts in strain development would be required to enable direct glucose utilization for methanogenesis. ImportanceThe known range of methanogenic growth substrates is very limited and the most reduced carbon compound to support organotrophic growth of M. acetivorans is pyruvate. Yet, gluconeogenesis and glycolysis, i. e., mobilization of stored glycogen, which is known to occur in M. acetivorans makes the capacity of glycolytic methanogenesis in this organism seem feasible. Although this trait could be engineered in M. acetivorans by introducing a single gene, the finding that it could not sustain growth of the organism, not even as an anabolic carbon source, demonstrates that methanogenesis is not easily compatible with carbohydrate utilization, thus probably requiring extensive metabolic rewiring.

microbiology↗

bioRxiv2024

Functional properties of a disease mutation for migraine in Kv2.1/6.4 channels

Voltage-gated potassium (Kv) channels are integral to cellular excitability, impacting the resting membrane potential, repolarization, and shaping action potentials in neurons and cardiac myocytes. Structurally, Kv channels are homo or heterotetramers comprising four -subunits, each with six transmembrane segments (S1-S6). Silent Kv (KvS), includes Kv5.1, Kv6.1-6.4, Kv8.1-8.2, and Kv9.1-9.3, they do not form functional channels on their own but modulate the properties of heteromeric channels. Recent studies have identified the Kv6.4 subunit as a significant modulator within heteromeric channels, such as Kv2.16.4. The Kv2.16.4 heteromer exhibits altered biophysical properties, including a shift in voltage-dependent inactivation and a complex activation. Current genetic studies in migraine patients have revealed a single missense mutation in the Kv6.4 gene. The single missense mutation, L360P is in the highly conserved S4-S5 linker region. This study aims to demonstrate the biophysical effects of the L360P mutation in Kv2.1 6.4 channels with a fixed 2:2 stoichiometry, using monomeric (Kv2.1/6.4) and tandem dimer (Kv2.1_6.4) configurations. Our findings suggest that the L360P mutation significantly impacts the function and regulation of Kv2.1/6.4 channels, providing insights into the molecular mechanisms underlying channel dysfunction in migraine pathology. Statement of significanceThis study elucidates the biophysical properties of the Kv6.4 L360P mutation, providing insights into its role in Kv2.1 6.4 channel function. Given the high conservation of the leucine residue in the Kv channel family and its association with migraine, our findings have significant implications for understanding the molecular basis of migraine pathophysiology. By analyzing channels with a fixed 2:2 stoichiometry, we highlight the impact of the L360P mutation on channel gating and inactivation. This research advances the knowledge of the silent Kv6.4 channel mechanism and its role in pathophysiology.

biophysics↗

bioRxiv2020

Functional and structural characterization of interactions between opposite subunits in HCN pacemaker channels

Hyperpolarization-activated and cyclic nucleotide (HCN) modulated channels are tetrameric cation channels. In each of the four subunits, the intracellular cyclic nucleotide-binding domain (CNBD) is coupled to the transmembrane domain via a helical structure, the C-linker. High-resolution channel structures suggest that the C-linker enables functionally relevant interactions with the opposite subunit, which might be critical for coupling the conformational changes in the CNBD to the channel pore. We combined mutagenesis, patch-clamp technique, confocal patch-clamp fluorometry, and molecular dynamics simulations to show that residue K464 of the C-linker is essential for stabilizing the closed state of the mHCN2 channel by forming interactions with the opposite subunit. MD simulations revealed that both cAMP and K464E induce a rotation of the intracellular domain relative to the channel pore, weakening the autoinhibitory effect of the unoccupied CL-CNBD region. The adopted poses are in excellent agreement with structural results.

biophysics↗

bioRxiv2020

Pathways of inter- and intrasubunit allosteric signaling in the C-linker disk and cyclic nucleotide-binding domain of HCN2 channels

Opening of hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels is controlled by membrane hyperpolarization and binding of cyclic nucleotides to the tetrameric cyclic nucleotide-binding domain (CNBD), attached to the C-linker disk (CL). Confocal patch-clamp fluorometry revealed a pronounced cooperativity of ligand binding among protomers. However, by which pathways allosteric signal transmission occurs remained elusive. Here, we investigate how changes in the structural dynamics of the CL- CNBD of mouse HCN2 upon cAMP binding relate to inter- and intrasubunit signal transmission. Applying a rigidity theory-based approach, we identify two intersubunit and one intrasubunit pathways that differ in allosteric coupling strength between cAMP binding sites or towards the CL. These predictions agree with results from electrophysiological and patch-clamp fluorometry experiments. Our results map out distinct routes within the CL-CNBD that modulate different cAMP binding responses in HCN2 channels. They signify that functionally relevant submodules may exist within and across structurally discernable subunits in HCN channels.

biophysics↗