Whether a molecular motor can spontaneously organize actin filaments into bundles has remained an open question despite decades of in vitro investigation. Here, we show that the dimeric myosin-X, essential for filopodia initiation and extension in cells, is capable of sorting actin filaments into parallel bundles, gathering barbed ends within 1-2 micrometers. We observe that myosin-X processivity is comparable on single filaments and on bundles induced by myosin-X or fascin. Upon reaching barbed ends, myosin-X slows down the addition or removal of actin subunits, in a myosin density-dependent manner. Furthermore, the funneling of myosin-X towards the remaining filaments at the bundle tip increases motor density and triggers dynamic clustering. Together, we propose that the motor activity of myosin-X is sufficient to initiate filopodia, independently of passive crosslinkers such as fascin or fimbrin.
Kools, W., Faour, S., Carlier, A., Hristova, T., Sirkia, M. E., Chaix, L., Lee, A., Martin, P., Houdusse, A., Romet-Lemonne, G., JEGOU, A.
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