The Measurement of the Stepping Force of Purified Zymogen Graunles using a Single Beam Optical Trap

Abstract

The transportation of vesicles is important for the development, organization, and functioning of all cellular organisms. The failures of vesicle transportation cause many diseases and chronic illnesses associated with the malfunctioning of these systems. The molecular motors responsible for these vesicle transportations supply the energy for locomotion by exchanging chemical energy into mechanical force. A particular vesicle, zymogen granules (ZGs), digestive enzymes secreted by the pancreas are studied. Recently, the mass spectroscopy experiment showed that myosin Ib, myosin VIIb, and Myosin Vc were found on the ZGs. To understand what the molecular motors involved in the vesicle trafficking, we purify ZGs from rat pancreas and examine the stepping manner and force that is used by a single beam optical tweezer. The average speed of the ZGs is around 100 nm/sec, which is similar to our previous study of two myosin Vc molecules tagged with DNA. The results indicate that the stepping is unidirectional with a 16-nm to 72-nm step-size, while some of the steps are a back-and-force ensemble stepping along the axis of actin filaments. The average force and maximum force in the optical trap are 0.1 pN and 10 pN, respectively. The typical force of a single molecular motor has a range of 1 pN to 5 pN. Thus, our finding in the unidirectional movement can be created by a single molecule motor. Our results suggest that most steps maybe created by myosin Vc.