Transformation of the Nonprocessive Fast Skeletal Myosin II into a Processive Motor.

Myosin family motors play diverse cellular roles. Precise insights into how the light chains contribute to the functional variabilities among myosin motors, however, remain unresolved. Here, it is demonstrated that the fast skeletal muscle myosin II isoform myosin heavy chain (MHC-IID) can be transformed into a processive motor, by simply replacing the native regulatory light chain MLC2f with the regulatory light chain variant MLC2v from the slow muscle myosin II. Single molecule kinetic analyses and optical trapping measurements of the hybrid motor reveal marked changes such as increased association rate of myosin toward adenosine triphosphate (ATP) and actin by more than twofold. The direct consequence of high adenosine diphosphate (ADP) affinity and increased actin rebinding is the altered overall actomyosin association time during the cross-bridge cycle. The data indicate that the MLC2v influences the duty ratio in the hybrid motor, suggestive of promoting interhead communication and enabling processive movement. This finding establishes that the regulatory light chain fine-tunes the motor's mechanical output that may have important implications under physiological conditions. Furthermore, the success of this approach paves the way to engineer motors from a known motor protein element to assemble highly specialized biohybrid machines for potential applications in nano-biomedicine and engineering.