Protein Name

Myosin V complexed with calmodulins


Gallus gallus (chicken)

Biological Context

Myosin is a motor protein that plays key roles in various functions such as muscle contraction (myosin II, MyoII) or vesicle transport (myosin V, MyoV). MyoV moves along actin filaments to transport organelles, vesicles and mRNAs using the energy of ATP hydrolysis. In its activated state, MyoV works in a hand-over-hand manner and delivers its cargo to the barbed (+) end of the actin filament.

The mechanism by which the MyoV returns to the start position after cargo delivery remains unknown. However, the inactive structure described here indicates a recycling mechanism for MyoV by "running up the down escalator". The "down escalator" is the actin filament, which moves in the opposite direction from activated MyoV by the treadmilling process. The activated MyoV with cargo moves quickly along the actin filament by using the energy of ATP. When it reaches the actin (+) end, it puts off the cargo and goes back to the start position through the "escalator" (Fig. 1).

Structure Description


The inactivated MyoV has a compact structure compared to its activated state. This structure has been determined by using cryoelectron tomography images on which known PDB structures are superimposed.

MyoV has two chains that have motor domains on the amino-terminal heads, followed by lever arms with 6 calmodulin molecules. After that, it has a coiled-coil dimerization domain (S2) and a carboxy-terminal cargo-binding domain (Fig. 2). It should be noticed that although the cargo binding domain-like structures were observed on cryoelectron tomography images, these domains were omitted due to the lack of the structure in the PDB.

The inactivated MyoV folds at the border of its lever arm and coiled coil regions, and a binding occurs between the motor and cargo domains. The actin binding region of the motor domain is still free because the cargo domain binds to the loop 1 region of the motor domain. Thus, the motor domain can bind to actin filaments even in the inactivated state and, in fact, this structure was also observed.

It is expected in the future that an X-ray structure of inactivated MyoV be solved and that the various kinds of its binding pattern to actin be identified. It is hoped that eventually a series of MyoV dynamics is elucidated.

model_2DFS structure_2DFS
(Fig.1) Recycle model of myosin V

Actin filament shown as the light blue cylinder perform a treadmilling process from its plus to its minus ends. The left figure shows an activated MyoV which brings its cargo (green) to the plus end of actin. The right figure shows an inactive MyoV bound to actin and going back to the minus end through actin treadmilling.
(Fig.2) Inactive structure of myosin V

The two heavy chains of MyoV, colored blue and light blue, contain head domains, lever arms and coiled-coil regions. Calmodulins are colored green and light green. The light blue cylinder is the actin filament. The cargo-binding domains are omitted due to the lack of structure in PDB.

Protein Data Bank (PDB)



Liu, J. Taylor, D.W. Krementsova, E.B. Trybus, K.M. Taylor, K.A.; "Three-dimensional structure of the myosin V inhibited state by cryoelectron tomography"; Nature; (2006) 442:208-211 PubMed:16625208.


author: Naoya Fujita

Japanese version:PDB:2DFS