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

Abstract

Summary 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.

Structural basis of myosin V Rab GTPase-dependent cargo recognition

“…Whereas this region is conserved in vertebrate Myo5 and yeast Myo2p, it is not in Myo4p (18). Interestingly, the same Myo5 residues are involved in interaction with Sec15-a subunit of the exocyst showing a link between the motor and the tethering complexes (13). It is thus interesting that the SD-2 GTD region involved in both inhibition of the motor and its binding to the exocyst upon activation has been conserved in yeast Myo2p and vertebrate Myo5.…”

“…The yeast Myo5 Myo2p transports secretory vesicles via a Rab GTPase cascade involving Ypt31/32 and Sec4 (Rab11 and Rab8 homologs, respectively) (13), and in Drosophila, Myo5 also binds Rab11 to drive secretory vesicle movement (14). In contrast, there are Myo5 isoformspecific interactions between the GTD and specialized adaptors, such as Myo5A association with MLPH.…”

SEC-10 and RAB-10 coordinate basolateral recycling of clathrin-independent cargo through endosomal tubules in Caenorhabditis elegans

“…Rab proteins allow the directional movement of various membrane carriers along the microtubule cytoskeleton through a direct or indirect association with motor proteins (56). In addition, a connection of the exocyst as adaptors with microtubules and actin-based transport has been suggested (15,(57)(58)(59).…”

RhoGTPase-binding proteins, the exocyst complex and polarized vesicle trafficking

“…34 In budding yeast, Sec4 interacts with the exocyst via Sec15, a linker molecule between exocyst subunits on the vesicle and on the plasma membrane. 35 A second important effector of Sec4 is Sro7, which binds to the plasma membrane SNARE Sec9. 36 This specific interaction enables efficient coordination between the arrival of a secretory vesicle to the plasma membrane and SNARE activation for vesicle fusion in a precisely timed manner.…”