Growth of fingerlike protrusions driven by molecular motors.

The actin cortex is an important part of the motile machinery of a eucaryotic cell. The cortex is steadily reorganized, for example, through the action of molecular motors forming active crosslinks between pairs of actin filaments. Here, the effect of correlations between molecular motors on the induced relative motion of two aligned filaments is investigated. It is found that the average relative velocity between filaments depends nonmonotonically on the motor concentration. Depending on the properties of the filaments' ends, the active interaction between filaments of the same orientation may lead either to a complete overlap or to separation. In addition to pure actin polymerization the active separation of filaments might be involved in the growth of long fingerlike protrusions (filopods).