Biology subjects

Samso, M.

Publications and source records attributed to Samso, M..

5 recordsLinked to original sources

bioRxiv2025

High burden of premature ventricular contractions upregulates transcriptional markers of inflammation and promotes adverse cardiac remodeling linked to cardiomyopathy

Premature ventricular contractions (PVCs) are the most prevalent ventricular arrhythmia in adults. High PVC burden can lead to left ventricular (LV) systolic dysfunction, eccentric hypertrophy, and an increased risk of heart failure (HF) and sudden cardiac death (SCD). Inadequate angiogenesis is a key determinant in the transition from adaptive to maladaptive cardiac hypertrophy and fibrosis is a risk factor for arrhythmia and SCD. To quantitatively assess structural remodeling and transcriptional alterations in PVC-induced cardiomyopathy (PVC-CM), animals were implanted with modified pacemakers to deliver bigeminal PVCs (200-220 ms coupling interval) for 12 weeks. Collagen deposition and interstitial ultrastructure of LV samples were analyzed using light and transmission electron microscopy, respectively. Pericytes, fibroblasts, myocytes, smooth muscle, and endothelial cells were imaged using confocal microscopy, quantified with an artificial intelligence-based segmentation analysis, and compared using hierarchical statistics. Transcriptional changes were assessed via RNAseq. Although cardiomyocytes hypertrophied in PVC-CM, capillary rarefaction was overcome by an increase in capillary- to-myocyte ratio. Additionally, thicker blood vessels were more abundant in PVC-CM. Fibroblast-to-myocyte ratio more than doubled, interstitial collagen fibers increased, and interstitial space thickened in PVC-CM. Transcripts involved in interstitial remodeling, inflammatory response, and alarmins were strongly elevated in PVC-CM. Overall, while the angiogenic response meets the metabolic demands of cardiac hypertrophy, upregulated markers of inflammation and cardiomyopathy linked to reactive fibrosis collectively represent an adverse LV remodeling that heightens the risk of HF and SCD in PVC-CM.

physiology↗

bioRxiv2024

Dantrolene inhibition of ryanodine receptor 1 carrying the severe malignant hyperthermia mutation Y522S visualized by cryo-EM

Mutations in the skeletal isoform of the ryanodine receptor (RyR1) pose grave risks during anesthesia or treatment with succinylcholine muscle relaxants. These can trigger a potentially lethal malignant hyperthermia (MH) episode via intracellular calcium increase mainly from RyR1 channel leakage. Dantrolene is the primary antidote to prevent death. The main target of dantrolene is RyR1, however little is known about the mechanism of inhibition. Cryo-EM of dantrolene bound to the severe MH Y522S RyR1 mutant in the closed and open states at 2.5-3.3 [A] resolution revealed that the drug binds to the channels cytoplasmic assembly, far from the ion gate, interacting with residues W882, W996 and R1000 in the P1 domain. The finding was validated by Ca2+ imaging and [3H]ryanodine binding in WT and alanine mutants. Dantrolene reduced channel opening probability by restricting the central activation module, "cooling down" the primed conformation caused by the mutation. These findings shed light on dantrolenes mechanism against MH and suggest avenues for developing more effective therapeutics.

biochemistry↗

bioRxiv2024

Interplay between Mg2+ and Ca2+ at multiple sites of the ryanodine receptor

RyR1 is an intracellular Ca2+ channel important in excitable cells. Ca2+ activates it at low concentrations and inhibits it at high concentrations. Mg2+ is the main physiological RyR1 inhibitor, an effect that is overridden upon activation. Despite the significance of Mg2+-mediated inhibition, the molecular-level mechanisms remain unclear. We determined two cryo-EM structures of RyR1 with Mg2+ up to 2.8 [A] resolution, identifying multiple Mg2+ binding sites. Mg2+ inhibits at the known Ca2+ activating site and we propose that the EF hand domain is an inhibitory divalent cation sensor. Both divalent cations bind to ATP within a crevice, contributing to the precise transmission of allosteric changes within the enormous channel protein. Notably, Mg2+ inhibits RyR1 by interacting with the gating helices as validated by molecular dynamics. This structural insight enhances our understanding of how Mg2+ inhibition is overcome during excitation.

biophysics↗

bioRxiv2022

Cryo-EM structure of the Type IV pilus extension ATPase from enteropathogenic Escherichia coli

Type 4 pili (T4P) are retractable surface appendages found on numerous bacteria and archaea that play essential roles in various microbial functions, including host colonization by pathogens. An ATPase is required for T4P extension, but the mechanism by which chemical energy is transduced to mechanical energy for pilus extension has not been elucidated. Here we report the cryo-electron microscopy (cryo-EM) structure of the BfpD ATPase from enteropathogenic Escherichia coli (EPEC) in the presence of either ADP or a mixture of ADP and AMP-PNP. Both structures, solved at 3 [A] resolution, reveal the typical toroid shape of AAA+ ATPases and unambiguous six-fold symmetry. This six-fold symmetry contrasts with the two-fold symmetry previously reported for other T4P extension ATPase structures, all of which were from thermophiles and solved by crystallography. In the presence of the nucleotide mixture, BfpD bound exclusively AMP-PNP and this binding resulted in a modest outward expansion in comparison to the structure in the presence of ADP, suggesting a concerted model for hydrolysis. De novo molecular models reveal a partially open configuration of all subunits where the nucleotide binding site may not be optimally positioned for catalysis. ATPase functional studies reveal modest activity similar to that of other extension ATPases, while calculations indicate that this activity is insufficient to power pilus extension. Our results reveal that, despite similarities in primary sequence and tertiary structure, T4P extension ATPases exhibit divergent quaternary configurations. Our data raise new possibilities regarding the mechanism by which T4P extension ATPases power pilus formation.

microbiology↗

bioRxiv2021

Ca2+-inactivation of the mammalian ryanodine receptor type 1 in a lipidic environment revealed by cryo-EM

Activation of the intracellular Ca2+ channel ryanodine receptor (RyR) triggers a cytosolic Ca2+ surge, while elevated cytosolic Ca2+ inhibits the channel in a negative feedback mechanism. Cryo-EM carried out under partially inactivating Ca2+ conditions revealed two conformations of RyR1, an open state and an inactivated state, resolved at 4.0 and 3.3 [A] resolution, respectively. RyR1s were embedded in nanodiscs with two lipids resolved at each inter-subunit crevice. Ca2+ binding to the high affinity site engages the central (CD) and C-terminal domains (CTD) into a quasi-rigid unit, which separates the S6 four-helix bundle and opens the channel. Further out-of-plane rotation of the quasi-rigid unit pushes S6 towards the central axis, closing (inactivating) the channel. The inactivated conformation is characterized by a downward conformation of the cytoplasmic assembly, a tightly-knit subunit interface contributed by a fully occupied and partially remodeled Ca2+ activation site, and two salt bridges between the EF hand domain and the S2-S3 loop of the neighboring subunit validated by naturally-occurring diseasecausing mutations. Ca2+ also bound to ATP, mediating a tighter interaction between S6 and CTD. Our study suggests that the closed-inactivated is a distinctive state of the RyR1 and its transition to the closed-activable state is not a simple reverse of the Ca2+ mediated activation pathway.

physiology↗