This image shows the active, open state of IRSp53 (top) and inactive, closed (bottom) state of IRSp53. In the closed state, cells do not generate filopodia as shown in the right bottom image (green=IRSp53, red=cdc42, and blue=actin, the most abundant protein in the cytoskeleton). The arrow between the two states indicates that the synergistic binding of Cdc42, cytoskeleton proteins (called downstream effectors of IRSp53 and includes the tumor-promoting factor Eps8) and the inherent attraction for the cell membrane, bring IRSp53 to specific locations on the cell membrane in which to change the shape of the cell. Chief among this reshaping activity is generating filopodia, the long thin objects coming off the cell in the top right image (color scheme as right bottom image). Note the change in pattern of the green and red show that IRSp53 and cdc42 are working together and moving to many different locations around the cell.
Roberto Dominguez, Ph.D., David Kast, Ph.D., Perelman School of Medicine, University of Pennsylvania