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Myosin X

updated 26/5/02

Myosin X is widely expressed in many tissues in mammalian cells. Uniquely amongst the myosins, the tail of myosin X contains three PH domains, that may be actin-binding regions or phosphoinositide-binding regions.  The cargo of myosin X is presently unknown, but it is known that this motor protein is responsible for some intrafilapodial motility (Berg & Cheney, 2002).  Myosin X is concentrated at the tips of filopodia and myosin X rich regions travel forward and backward along filopods Berg & Cheney, 2002).  Forward motion may result from the motor activity of myosin X itself, but to date the only myosins known to travel in the opposite (pointed end) direction are myosin VI and myosin IX, so suspicion must fall on these myosins as the other motor, as filament polarity is uniformly barbed end forwards. Myosin X over-expression causes an increase in the number and length of filopodia in COS-7 cells (Berg & Cheney, 2002).
The structure of myosin X is similar to myosin V except that it has 6 IQ motifs instead of 12, and like Myosins VII and XV in that it contains a myosin homology 4 (MyTH4) domain.
The light chains may be either calmodulin itself or calmodulin-like proteins

Berg, J.S., Derfler, B.H., Pennisi, C.M., Corey, D.P., & Chenney, R.E. (2000) J.Cell Sci. 113, 3439-3451.

Berg, J. S. & Cheney, R. E. (2002) Myosin-X is an unconventional myosin that undergoes intrafilodial motility. Nature Cell Biol. 4, 246-250.

Homma, K., Saito, J., Ikebe, R. & Ikebe, M. (2001) Motor function and regulation of myosin X., J.Biol.Chem. 276, 34348-3454.

Rogers, M. S. & Strehler, E. E. (2001) The tumour-sensitive calmodulin-like protein is a specific light chain of human unconventional myosin X., J.Biol.Chem. 276, 12182-12189.

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