Biology subjects

Spahiu, E.

Publications and source records attributed to Spahiu, E..

5 recordsLinked to original sources

bioRxiv2026

Myotropes unveil two myosin cycles with distinct kinetics and stroke size

Cardiac contraction relies on cyclic interactions between myosin II motors and actin filaments, powered by the free energy of ATP turnover. Targeting of this fundamental process has emerged as a promising therapeutic strategy; Mavacamten, a cardiac myosin inhibitor was recently approved for treating obstructive hypertrophic cardiomyopathy whereas omecamtiv mecarbil was developed as a myosin activator for heart failure. Both myotropes bind to the same myosin pocket but their mechanisms of action remain incompletely understood. Here, we investigate these using optical tweezers mechanoenzymology and single-molecule fluorescence-based actomyosin kinetics applied to {beta}-myosin from donor hearts and recombinant human {beta}-myosin subfragment 1. Our findings reveal unexpected layers of complexity. Both mavacamten and omecamtiv mecarbil partially slow the ATP turnover, giving one fast (similar to physiological) and one drug-induced slow ATP turnover cycle at saturating drug concentrations with different rate-limiting steps for the two compounds. In one of the parallel cycles, mavacamten increases stroke size and appreciably delays the power-stroke, allowing direct visualization of a strongly bound pre-power-stroke state. No power-stroke delay is seen in the other cycle, but a reduced stroke size is observed. Our findings uncover a new paradigm in cardiac regulation at the single-molecule level, demonstrating partial inhibition of myosin as a powerful therapeutic strategy.

biophysics↗

bioRxiv2026

Single-molecule analysis sheds light on cardiac myosin dysfunction due to hypertrophic cardiomyopathy mutation A57D in ventricular myosin light chain-1 (MLC1v)

Ventricular myosin light chain-1 (MLC1v) is a key structural and function-modulating component of the {beta}-cardiac myosin ({beta}M-II) motor complex. Single-point mutations in MLC1v are linked to severe forms of hypertrophic cardiomyopathy (HCM) and sudden cardiac death (SCD) at a young age. However, the molecular mechanisms underlying the motor dysfunction responsible for HCM phenotype development are not fully understood. Here, we investigated native {beta}M-II motors isolated from septal myectomy sample of an HCM patient, harboring a rare homozygous mutation in MLC1v (A57D). Using a pure population of mutant motors (MUT), and sensitive single-molecule functional analysis approach, we directly assessed the primary functional alterations in {beta}M-II bearing A57D MLC1v mutation. In optical trap single-molecules measurements, the mutant motors displayed increased actomyosin (AM) interaction duration in strongly bound state (ton), corresponding to 3-fold reduced AM detachment rate than wild type myosin (WT). The MUT myosin also generated a shorter powerstroke size ({delta}). Ensemble average analysis of AM interaction events demonstrated that both the first powerstroke ({delta}1) associated with Pi release and the second powerstroke ({delta}2) linked to ADP release were reduced in MUT myosin. Moreover, the increased actomyosin cross-bridge stiffness in the AM.ADP state was observed for MUT compared to WT motors. Consistent with slower AM detachment rate and shorter stroke size, reconstituted human mutant {beta}M-II displayed slower actin filament gliding speed. Alterations in sarcomere-level mechanics included increased Ca2+ sensitivity of force generation and prolonged relaxation time, as predicted by FiberSim modelling. Molecular dynamics simulations indicated that the substitution of alanine by aspartate altered MLC1v interactions with myosin heavy chain (MyHC) and light chain 2 (MLC2v), affecting the curvature and flexibility of the lever arm. Overall, these studies establish the molecular mechanism underlying the primary myosin dysfunction due to A57D MLC1v mutation and further highlight the crucial role of MLC1v-mediated regulation of myosin function. Understanding the precise changes in the mutant myosins biomechanical properties is directly relevant to comprehending the initial triggers for pathological cardiac remodeling in HCM patients and designing tailored therapeutic interventions.

biophysics↗

bioRxiv2022

Cardiac ventricular myosin and slow skeletal myosin exhibit dissimilar chemo-mechanical properties despite the same myosin heavy chain isoform.

The myosin II motors are ATP-powered, force-generating machines driving cardiac and muscle contraction. Myosin II heavy chain isoform-beta ({beta}-MyHC) is primarily expressed in the ventricular myocardium and slow-twitch muscle fibers, such as in M. soleus. M. soleus-derived myosin II (SolM-II) is often used as an alternative to the ventricular {beta}-cardiac myosin ({beta}M-II); however, the direct assessment of detailed biochemical and mechanical features of the native myosins is limited. By employing the optical trapping method, we examined the mechanochemical properties of the native myosins isolated from rabbit heart ventricle and M. soleus muscles at the single-molecule level. Contrary to previous reports, the purified motors from the two tissue sources, despite the same MyHC isoform, displayed distinct motile and ATPase kinetic properties. {beta}M-II was [~]threefold faster in the actin filament-gliding assay than SolM-II. The maximum acto-myosin (AM) detachment rate derived in single-molecule assays was [~]threefold higher in {beta}M-II. The stroke size for both myosins was comparable. The stiffness of the AM rigor cross-bridge was also similar for both the motor forms. The stiffness of {beta}M-II was found to be determined by the nucleotide state of the actin-bound myosin. Our analysis revealed distinct kinetic differences, i.e., a higher AM detachment rate for the {beta}M-II, corresponding to the ADP release rates from the cross-bridge, thus elucidating the observed differences in the motility driven by {beta}M-II and SolM-II. These studies have important implications for the future choice of tissue sources to gain insights into cardiomyopathies

biophysics↗

bioRxiv2020

Activation of Macrophages by CpG DNA and LPS: an FTIR Spectroscopic Study

The innate immune response triggered by CpG DNA can improve host survival following pathogen challenge. Whether CpG ODN-mediated immune activation leads to global molecular changes in cells that are detectable by FTIR spectroscopy is currently unknown. Here, we used Attenuated Total Reflectance (ATR) Fourier Transform Infrared (FTIR) spectroscopy to monitor the molecular changes in murine macrophage RAW 264.7 cells upon activation with CpG DNA and lipopolysaccharide (LPS). By PCA analysis, we identified the sources of variation to follow with detailed spectral analysis. CpG DNA and LPS treatment increase the total nucleic acid concentration from the early periods post-activation, and DNA synthesis follows RNA synthesis. RNA-specific peak shows the activation state of macrophages in early periods post-treatment. CpG DNA and LPS result in an initial rapid increase in the total protein concentration, leveling off two hours post-activation. Both activated groups increase the concentration of fatty acids, triglycerides, and cholesterol, pointing out to a shared synthesis pathway and de novo lipogenesis. This study, for the first time, demonstrates the use of FTIR spectroscopy as an independent modality to monitor the activation dynamics of murine macrophages upon activation with CpG DNA and LPS.

biophysics↗

bioRxiv2020

Enzyme Kinetics and Inhibition parameters of Human Leukocyte Glucosylceramidase

Glucosylceramidase (GCase) is a lysosomal enzyme that catalyzes the cleavage of {beta}-glucosidic linkage of glucocerebroside (GC) into glucose and ceramide; thereby, plays an essential function in the degradation of complex lipids and the turnover of cellular membranes. The growing list of 460 mutations in the gene coding for it--glucosylceramidase beta acid 1 (GBA1)--is reported to abolish its catalytic activity and decrease its enzyme stability, associating it with severe health conditions such as Gaucher disease (GD), Parkinson Disease and Dementia with Lewy bodies. Although the three-dimensional structure of wild type glucosylceramidase is elucidated, little is known about its features in human cells. Moreover, alternative sources of GCase that prove to be effective in the treatment of diseases with enzyme treatment therapies, impose the need for simple and cost-effective procedures to study the enzyme behaviour. This work, for the first time, shows a well established, yet simple, cost- and time-efficient protocol for the study of GCase enzyme in human leukocytes by the artificial substrate PNPG. Characterization of the enzyme in human leukocytes for activation parameters (optimal pH, Km, and Vmax) and enzyme inhibition, was done. The results indicate that the optimum pH of GCase enzyme with PNPG is 5.1. The Km and Vmax values were 12.6mM and 333 U/mg, respectively. Gluconolactone successfully inhibits GCase in a competitive manner, with a Ki value of 0.023 mM and IC 50 of 0.047 mM. Glucose inhibition was uncompetitive with a Ki of 1.94 mM and IC50 of 55.3 mM. This is the first report for the inhibitory effect of glucose, {delta}-gluconolactone on leukocyte GCase activity.

biochemistry↗