RUB » Bibliotheksportal

Roua Hassoun, Constanze Erdmann, Sebastian Schmitt, Setsuko Fujita-Becker, Andreas Mügge, Rasmus R. Schröder, Matthias Geyer, Mina Borbor, Kornelia Jaquet, Nazha Hamdani, Hans Georg Mannherz

• Human wild type (wt) cardiac \(\alpha\)-actin and its mutants p.A295S or p.R312H and p.E361G correlated with hypertrophic or dilated cardiomyopathy, respectively, were expressed by using the \(\textit {baculovirus/Sf21}\) insect cell system. The c-actin variants inhibited DNase I, indicating maintenance of their native state. Electron microscopy showed the formation of normal appearing actin filaments though they showed mutant specific differences in length and straightness correlating with their polymerization rates. TRITC-phalloidin staining showed that p.A295S and p.R312H exhibited reduced and the p.E361G mutant increased lengths of their formed filaments. Decoration of c-actins with cardiac tropomyosin (cTm) and troponin (cTn) conveyed \(Ca^{2+}\)-sensitivity of the myosin-S1 ATPase stimulation, which was higher for the HCM p.A295S mutant and lower for the DCM p.R312H and p.E361G mutants than for wt c-actin. The lower \(Ca^{2+}\)-sensitivity of myosin-S1 stimulation by both DCM actin mutants was corrected by the addition of levosimendan. \(Ca^{2+}\)-dependency of the movement of pyrene-labeled cTm along polymerized c-actin variants decorated with cTn corresponded to the relations observed for the myosin-S1 ATPase stimulation though shifted to lower \(Ca^{2+}\)-concentrations. The N-terminal C0C2 domain of cardiac myosin-binding protein-C increased the \(Ca^{2+}\)-sensitivity of the pyrene-cTM movement of bovine, recombinant wt, p.A295S, and p.E361G c-actins, but not of the p.R312H mutant, suggesting decreased affinity to cTm.