MyoDesign-Partners

Dynamic cell structures highly depend on allosteric machines that interact with cytoskeleton tracks and cargoes to cooperatively generate directional force or movement. Myosins are such molecular motors that use ATP to power mechanical work on F-actin to transport or anchor, tension membranes, tether vesicles, contract or work as mechanical force sensors, to contribute for example in cell migration and in the generation of actin-rich cellular protrusions. They play in fact key roles in almost all major events of a cell life sometimes in conjunction with microtubule-based motors. However, our molecular understanding of their exact action in these events and on the cues that activate them at the right time and the right place in cells is still very limited. We also lack understanding on the importance of structural adaptations that differ among members of the superfamily to provide specific motility functions. To perform their multiple tasks, myosin motors interact with a wide variety of partners/effectors. Whether partner recognition is sufficient in some cases to activate these molecular motors or whether cellular cues (Ca2+ ions, phosphorylation, lipids) must intervene to unfold the motor and allow it to interact efficiently with F-actin is still poorly understood. Moreover, how these effectors direct myosin to function as a transporter, a tether or an anchor in different cellular context are crucial questions that need to be explored to begin to understand the exact roles the motor plays in the different cellular processes for which it has been identified as an essential actor. Focusing on Myosin V and Myosin X, we propose with this ANR project to participate in this important field of investigation. With these myosins, we will study two processive motors adapted for distinct cellular functions and that play key roles in cell migration. The ultimate goal is to provide a mechanistic molecular understanding of how these motors know when and where to act and how the unique design and functionalities of these motors contribute to specific actions on particular tracks and compartments of the cell. For Myosin V, our specific goal is to study the multiple roles it can perform in the recycling pathways of cell receptors, which underlie for example processes such as learning and memory. Myosin V interacts with proteins participating in different steps of vesicle trafficking including short-range movement within actin cortex, vesicle tethering and fusion. A number of structures of Myosin V bound to several partners will define how the motor is regulated and how it operates to perform its multiple functions in translocating vesicles to the plasma membrane. For Myosin X, we will provide molecular understanding of its multiple roles in the formation and function of filopodia and invadopodia, these actin-filed protrusions that play major roles in migrating and invasive cells. We will define the motility properties of the motor with functional studies and define how its structural specific features contribute to these motility functions. We will also gain insights to define the roles played by Myosin X by discovering and studying multiple cellular partners of this myosin. The major innovation of this project is not only to address how partners regulate and define the function of myosin motors but also to link specific molecular insights derived from deep understanding of the structural adaptations of the motor to in vitro and cell biology assays that will determine which action the motor performs in different cellular processes. Four highly complementary teams will join efforts in this multi-disciplinary proposal to gain deep and wide knowledge on the specific roles of Myosins X and V. This research program will thus bridge molecular understanding of myosin motors to precise description of their action in the different cellular processes in which they participate.