Structural insights into filament recognition by cellular actin markers

Cellular studies of filamentous actin (F-actin) processes commonly utilize fluorescent versions of toxins, peptides and proteins that bind actin. While the choice of these markers has been largely based on availability and ease, there is a severe dearth of structural data for an informed judgment in employing suitable F-actin markers for a particular requirement. Here we describe the electron cryomicroscopy structures of phalloidin, lifeAct and utrophin bound to F-actin, providing the first high-resolution structures and comparison of widely used actin markers and their influence towards F-actin. Our results show that phalloidin binding does not induce conformations and lifeAct specifically recognizes ADP-actin state, which can be used as a sensor for distinguishing different nucleotide states of F-actin. The utrophin structural model aided designing minimal utrophin, which can be utilized as F-actin marker. Together, our study provides a structural perspective, where the binding sites of utrophin and lifeAct overlap with majority of actin binding proteins. Further offering an invaluable resource for researchers in choosing appropriate actin markers and generating new marker variants.