Li, X.D. et al. The globular tail domain puts on the brake to stop the ATPase cycle of myosin Va. Proc. Natl. Acad. Sci. USA 105, 1140-1145

Departments of Physiology and Cell Biology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 02/2008; 105(4):1140-5. DOI: 10.1073/pnas.0709741105
Source: PubMed


Myosin Va is a well known processive motor involved in transport of organelles. A tail-inhibition model is generally accepted for the regulation of myosin Va: inhibited myosin Va is in a folded conformation such that the tail domain interacts with and inhibits myosin Va motor activity. Recent studies indicate that it is the C-terminal globular tail domain (GTD) that directly inhibits the motor activity of myosin Va. In the present study, we identified a conserved acidic residue in the motor domain (Asp-136) and two conserved basic residues in the GTD (Lys-1706 and Lys-1779) as critical residues for this regulation. Alanine mutations of these conserved charged residues not only abolished the inhibition of motor activity by the GTD but also prevented myosin Va from forming a folded conformation. We propose that Asp-136 forms ionic interactions with Lys-1706 and Lys-1779. This assignment locates the GTD-binding site in a pocket of the motor domain, formed by the N-terminal domain, converter, and the calmodulin in the first IQ motif. We propose that binding of the GTD to the motor domain prevents the movement of the converter/lever arm during ATP hydrolysis cycle, thus inhibiting the chemical cycle of the motor domain.

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    • "How is Myo2p activated by secretory vesicles? In vitro studies with mammalian myosin-V have suggested that the motor undergoes autoinhibition through an interaction of the ATPasecontaining head domain and the cargo-binding tail domain, and key residues in the tail mediating this regulation have been identified (Liu et al., 2006; Thirumurugan et al., 2006; Li et al., 2008). An attractive model for Myo2p activation is that the autoinhibited motor becomes active by binding to the receptor complex on secretory vesicles. "
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    ABSTRACT: Cell organization requires motor-dependent transport of specific cargos along cytoskeletal elements. How the delivery cycle is coordinated with other events is poorly understood. Here we define the in vivo delivery cycle of myosin-V in its essential function of secretory vesicle transport along actin cables in yeast. We show that myosin-V is activated by binding a secretory vesicle and that myosin-V mutations that compromise vesicle binding render the motor constitutively active. About ten motors associate with each secretory vesicle for rapid transport to sites of cell growth. Once transported, the motors remain associated with the secretory vesicles until they undergo exocytosis. Motor release is temporally regulated by vesicle-bound Rab-GTP hydrolysis and requires vesicle tethering by the exocyst complex but does not require vesicle fusion with the plasma membrane. All components of this transport cycle are conserved in vertebrates, so these results should be generally applicable to other myosin-V delivery cycles.
    Developmental Cell 10/2012; 23(4):769-81. DOI:10.1016/j.devcel.2012.09.001 · 9.71 Impact Factor
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    • "Sequence alignment with mouse myosin Va and a further literature survey indicated that the corresponding amino acids (Lys1706 and Lys1779) from myosin Va are those that mediate the tail and head interaction in this myosin (Li et al., 2008). It has been suggested that tail folding and interaction with the head is a regulatory mechanism inhibiting myosin ATPase activity and the function of myosin Va (Li et al., 2008). This suggests that myosin XIK can fold and form a head–tail interaction. "
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    ABSTRACT: It has recently been found that among the 17 Arabidopsis myosins, six (XIC, XIE, XIK, XI-I, MYA1, and MYA2) have a major role in the motility of Golgi bodies and mitochondria in Nicotiana benthamiana and Nicotiana tabacum. Here, the same dominant negative tail fragments were also found to arrest the movement of Gogi bodies when transiently expressed in Arabidopsis plants. However, when a Golgi marker was transiently expressed in plants knocked out in these myosins, its movement was dramatically inhibited only in the xik mutant. In addition, a tail fragment of myosin XIK could inhibit the movement of several post-Golgi organelles, such as the trans-Golgi network, pre-vacuolar compartment, and endosomes, as well as total cytoplasmic streaming, suggesting that myosin XIK is a major player in cytoplasm kinetics. However, no co-localization of myosin tails with the arrested organelles was observed. Several deletion truncations of the myosin XIK tail were generated to corroborate function with localization. All deletion mutants possessing an inhibitory effect on organelle movement exhibited a diffuse cytoplasmic distribution. Point mutations in the tail of myosin XIK revealed that Arg1368 and Arg1443 are essential for its activity. These residues correspond to Lys1706 and Lys1779 from mouse myosin Va, which mediate the inhibitory head-tail interaction in this myosin. Therefore, such an interaction might underlie the dominant negative effect of truncated plant myosin tails and explain the mislocalization with target organelles.
    Journal of Experimental Botany 09/2011; 63(1):241-9. DOI:10.1093/jxb/err265 · 5.53 Impact Factor
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    • "The end of this first coiled-coil region is critical in stabilizing the folded triangular structure of Myo5a and prevents the conformational changes of the motor domain during the ATP turnover cycle, consequently inhibiting the actin-activated ATPase activity of the motor domain (Li et al., 2006, 2008; Sato et al., 2007). Very recently, Li et al. (2008) identified a conserved acidic residue (D136) in the motor domain and two conserved basic residues (K1706 and K1779) in the GTD as critical residues involved in this inhibition of Myo5a. "
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    ABSTRACT: Griscelli syndrome (GS) is a rare autosomal recessive disorder caused by mutations in either the myosin VA (GS1), RAB27A (GS2) or melanophilin (GS3) genes. The three GS subtypes are commonly characterized by pigment dilution of the skin and hair, due to defects involving melanosome transport in melanocytes. Here, we review how detailed studies concerning GS have contributed to a better understanding of the molecular mechanisms involved in vesicle transport and membrane trafficking processes. Additionally, we demonstrate that the identification and biological analysis of novel disease-causing mutations highlighted the functional importance of the RAB27A-MLPH-MYO5A tripartite complex in intracellular melanosome transport. As the small GTPase Rab27a is able to interact with multiple effectors, including Slp2-a and Myrip, we report on their presumed role in melanosome transport. Furthermore, we summarize data suggesting that RAB27B and RAB27A are functionally redundant and hereby provide further insight into the pathogenesis of GS2. Finally, we discuss how the gathered knowledge about the RAB27A-MLPH-MYO5A tripartite complex can be translated into a possible therapeutic application to reduce (hyper)pigmentation of the skin.
    Pigment Cell & Melanoma Research 03/2009; 22(3):268-82. DOI:10.1111/j.1755-148X.2009.00558.x · 4.62 Impact Factor
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