Article

The globular tail domain of myosin Va Functions as an inhibitor of the myosin Va motor

Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 09/2006; 281(31):21789-98. DOI: 10.1074/jbc.M602957200
Source: PubMed

ABSTRACT 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.

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    • "Therefore, an interaction between the head and tail domains is necessary and sufficient to regulate myosin V in vivo to achieve a normal distribution. The two internal loops present in mammalian myosin V coiled-coil stalks have been shown in vitro to be required for autoinhibition, likely because of the flexibility gained to bring the head and tail domains together (Li et al., 2006). Myo2p lacks these internal loops, though the length of the lever arm and coiled coil domains are nearly identical (21 and 24 nm, respectively). "
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    • "The globular tail domain (GTD) of MyoVa has been used as an inhibitor of myosin function since it lacks the motor domain and acts as a dominant negative construct (Li et al., 2006). "
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    • "This suggests the other segments are either unstable or very flexible. It has therefore come as a surprise that the off state is very sensitive to the length of this invisible part [14]. "
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