Blebbistatin Effects on Myosin Structural Dynamics

Blebbistatin is a potent, small molecule inhibitor specific for myosin II, the type of myosin found in human skeletal, cardiac, and smooth muscle. Myosin II is the motor protein in muscle that uses adenosine triphosphate (ATP) to drive force generation and muscle contraction by its interactions with actin. Blebbistatin is cell-permeable and works by binding directly to myosin II near its ATP binding site. The enzymatic activity of Dictyostelium myosin II was tested using a steady-state NADH-coupled ATPase assay in both the absence and presence of blebbistatin. The decrease in NADH concentration is coupled to breakdown of ATP into ADP and phosphate and was measured by spectrophotometry to obtain the rate at which myosin hydrolyzes ATP. Myosin’s enzymatic activity was reduced in the presence of blebbistatin. Electron paramagnetic resonance (EPR) was used to determine blebbistatin induced changes in myosin structural dynamics. A monofunctional spin label was attached to two specifically engineered cysteine residues (F270C.F535C) in myosin, near the blebbistatin binding site and actomyosin binding interface, respectively. Blebbistatin has the potential to be useful in treating certain muscular diseases and inhibiting cell motility by interfering with actomyosin interactions. These results are important for understanding how blebbistatin perturbs myosin’s structure and mechanistic molecular details of its inhibitory activity