The globular tail domain of myosin Va functions as an inhibitor of the myosin Va motor.
The actin-activated ATPase activity of full-length mammalian myosin Va is well regulated by Ca2+, whereas that of truncated myosin Va without the C-terminal globular tail domain (GTD) is not. Here, we have found that exogenous GTD is capable of inhibiting the actin-activated ATPase activity of GTD-deleted myosin Va. A series of truncated constructs of myosin Va further showed that the entire length of the first coiled-coil (coil-1) of the tail domain is critical for GTD-dependent regulation of myosin Va and that deletion of 58 residues from the C-terminal end of coil-1 markedly hampered regulation. Negative staining electron microscopy revealed that GTD-deleted myosin Va formed a "Y"-shaped structure, which was converted to a triangular shape, similar to the structure of full-length myosin Va in the inhibited state, by addition of exogenous GTD. In contrast, the triangular shape was not observed when the C-terminal 58 residues of coil-1 were deleted, even in the presence of exogenous GTD. Based on these results, we propose a model for the formation of the inhibited state of myosin Va. GTD binds to the C-terminal end of coil-1. The neck-tail junction of myosin Va is flexible, and the long neck enables the head domain to reach the GTD associated with the end of coil-1. Once the head interacts with the GTD, the triangular inhibited conformation is stabilized. Consistent with this model, we found that shortening of the neck of myosin Va by two IQ motifs abolished the regulation by GTD, whereas regulation was partially restored by shortening of coil-1 by an amount comparable to that of the two IQ motifs.
Li
Xiang-Dong
XD
Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655. Electronic address: Xiangdong.Li@umassmed.edu.
Jung
Hyun Suk
HS
Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655.
Mabuchi
Katsuhide
K
Muscle Research Group, Boston Biomedical Research Institute, Watertown, Massachusetts 02472.
Craig
Roger
R
Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655.
Ikebe
Mitsuo
M
Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655.
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D051379:Mice; D008854:Microscopy, Electron; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D018995:Myosin Heavy Chains / Q000737:chemistry* / Q000502:physiology; D024701:Myosin Type V / Q000737:chemistry* / Q000502:physiology; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D014162:Transfection
D020409:Molecular Motor Proteins; C513082:Myo5a protein, mouse; D000251:Adenosine Triphosphatases; D024701:Myosin Type V; D018995:Myosin Heavy Chains