Figure 1. Diagram of myosin-V in the active and inactive 14S conformation. (a) This shows a schematic view of active myosin-V with a vesicle bound to the cargo binding domain (CBD). Actin is light blue. Each myosin-V heavy chain has a motor domain (MD; red) and a lever arm (cyan) that has six calmodulin light chains (green) bound. An elongated rod domain has three predicted coiled-coil segments; the first (cyan) is broken at the PEST site, which begins at residue V1105, the second (blue) after residue A1234, the third (blue) extends to the CBD. The dynein light chain, labeled DLC, binds within the second uncoiled region. (b) Myosin-V in the inactive conformation folds up using interactions between the CBD and the motor domain. Binding to actin is limited to one head per actin filament. The structure has an asymmetric placement of the first coiled-coil segment relative to the CBDs. This might allow for further folding of the rod along the paired CBDs as suggested in reference [32]. If the inactive conformation binds actin strongly, it will stay bound while actin monomer addition to the (+) end displaces the actin filament toward the (–) end. (c) Electron micrograph of folded myosin-V bound to actin showing single headed actin binding. Same coloring scheme as in (b). Adapted from reference [23].

Figure 2. (a) Image of the Liu et al. 3-D reconstruction of the inactive conformer of myosin-V [23^••] with the crystal structure of the CBD [31^••] modeled in. The two CBDs, colored yellow and orange, and are placed between the motor domains, colored red and magenta. These CBDs probably come from adjacent molecules through domain swapping. In (a) and (b), the regions of the motor domain involved in CBD interaction are colored green (loop 1) and two other sites [27^••] are colored cyan. These sites all occur on the same side of the motor domain. The CBD can be modeled into the map density in numerous ways, but the one shown comes near to both sets of interaction sites. The CaM light chain bound to IQ1 is colored green. (b) Higher magnification view showing the relationship of the CBD interaction sites with the actin binding surface. (c) Yeast CBD crystal structure shown as a ribbon diagram for the two domains (domain 1 in blue; domain 2 in red). Those residues involved in vacuole-specific interactions on domain 1 are rendered in space filling and colored cyan; those residues involved in secretory vesicle transport (domain 2) are rendered in yellow. Note that these two regions are placed on opposite sides of the CBD.