Article

Myosin V Transports Secretory Vesicles via a Rab GTPase Cascade and Interaction with the Exocyst Complex

Life Sciences Institute, Department of Cell & Developmental Biology, University of Michigan, Ann Arbor, MI 48109-2216, USA.
Developmental Cell (Impact Factor: 10.37). 12/2011; 21(6):1156-70. DOI: 10.1016/j.devcel.2011.10.009
Source: PubMed

ABSTRACT Vesicle transport requires four steps: vesicle formation, movement, tethering, and fusion. In yeast, two Rab GTPases, Ypt31/32, are required for post-Golgi vesicle formation. A third Rab GTPase, Sec4, and the exocyst act in tethering and fusion of these vesicles. Vesicle production is coupled to transport via direct interaction between Ypt31/32 and the yeast myosin V, Myo2. Here we show that Myo2 interacts directly with Sec4 and the exocyst subunit Sec15. Disruption of these interactions results in compromised growth and the accumulation of secretory vesicles. We identified the Sec15-binding region on Myo2 and also identified residues on Sec15 required for interaction with Myo2. That Myo2 interacts with Sec15 uncovers additional roles for the exocyst as an adaptor for molecular motors and implies similar roles for structurally related tethering complexes. Moreover, these studies predict that for many pathways, molecular motors attach to vesicles prior to their formation and remain attached until fusion.

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    • "In the charge reversal myo2-3DR- REKE strain, GFP-Sec4 polarization is significantly restored, though not to quite to the same degree as seen in wild-type cells. Exocyst component Sec15-GFP was also polarized in the myo2-3DR-REKE allele (Fig. S1 C), suggesting that defects in polarized transport related to this site may not be completely caused by a compromised Sec15p–Myo2p interaction as has been previously reported (Jin et al., 2011), but instead caused by motor misregulation. "
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    ABSTRACT: Cell organization requires regulated cargo transport along cytoskeletal elements. Myosin V motors are among the most conserved organelle motors and have been well characterized in both yeast and mammalian systems. Biochemical data for mammalian myosin V suggest that a head-to-tail autoinhibitory interaction is a primary means of regulation, but the in vivo significance of this interaction has not been studied. Here we generated and characterized mutations in the yeast myosin V Myo2p to reveal that it is regulated by a head-to-tail interaction and that loss of regulation renders the myosin V constitutively active. We show that an unregulated motor is very deleterious for growth, resulting in severe defects in Myo2-mediated transport processes, including secretory vesicle transport, mitochondrial inheritance, and nuclear orientation. All of the defects associated with motor misregulation could be rescued by artificially restoring regulation. Thus, spatial and temporal regulation of myosin V in vivo by a head-to-tail interaction is critical for the normal delivery functions of the motor. © 2015 Donovan and Bretscher.
    The Journal of Cell Biology 05/2015; 209(3). DOI:10.1083/jcb.201411010 · 9.69 Impact Factor
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    • "mice, demonstrating a functional relationship between these proteins (Fig. 6A,B). Both Rab8a and Rab11a are known to bind myosin Vb (Lapierre et al., 2001; Roland et al., 2007; Jin et al., 2011). Therefore, to determine whether myosin Vb protein is involved in the localisation of Rab11a, we compared small intestine samples from a microvillus atrophy patient and a healthy individual (Fig. 6C), as microvillus atrophy patients are known to have mutations in the myosin Vb gene (Müller et al., 2008). "
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    Biology Open 12/2014; 4(1). DOI:10.1242/bio.20148532 · 2.42 Impact Factor
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    • "Alternatively, axonal Exoc3 and TC10 mRNAs might subserve different functions in the regulation of membrane exocytosis. For example, in yeast the myosin V homologue, Myo2, interacts with the exocyst including Sec6p/Exoc346. The presence of Exoc3 mRNA in regenerating axons might therefore be a reflection of increased transport of secretory vesicles while local TC10 translation in developing axons triggers PPV tethering to specific secretion sites within the growth cones. "
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