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Published online 8 March 2004. doi:10.1083/jcb.200310065
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 164, Number 6, 877-886
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Article

Myosin V

: regulation by calcium, calmodulin, and the tail domain



Dimitry N. Krementsov, Elena B. Krementsova, and Kathleen M. Trybus

Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405

Address correspondence to Kathleen M. Trybus, Dept. of Molecular Physiology and Biophysics, University of Vermont, 130 Health Science Research Facility, Burlington, VT 05405-0068. Tel.: (802) 656-8750. Fax: (802) 656-0747. email: trybus{at}physiology.med.uvm.edu

Calcium activates the ATPase activity of tissue-purified myosin V, but not that of shorter expressed constructs. Here, we resolve this discrepancy by comparing an expressed full-length myosin V (dFull) to three shorter constructs. Only dFull has low ATPase activity in EGTA, and significantly higher activity in calcium. Based on hydrodynamic data and electron microscopic images, the inhibited state is due to a compact conformation that is possible only with the whole molecule. The paradoxical finding that dFull moved actin in EGTA suggests that binding of the molecule to the substratum turns it on, perhaps mimicking cargo activation. Calcium slows, but does not stop the rate of actin movement if excess calmodulin (CaM) is present. Without excess CaM, calcium binding to the high affinity sites dissociates CaM and stops motility. We propose that a folded-to-extended conformational change that is controlled by calcium and CaM, and probably by cargo binding itself, regulates myosin V's ability to transport cargo in the cell.

Key Words: myosin V; calmodulin; calcium regulation; molecular motors; motility assay

D.N. Krementsov and E.B. Krementsova contributed equally to this paper.

Abbreviations used in this paper: dFull, full-length myosin V; dHMM, dilute heavy meromyosin V; HC, heavy chain; long-dHMM, a long heavy meromyosin lacking only the cargo-binding domain; MD2IQ, a monomer with the motor domain and the first two IQ motifs; WT, wild type.


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