The rapid turnover of branched actin networks underlies key in vivo processes such as lamellipodial extension, endocytosis, phagocytosis, and intracellular transport. However, our understanding of the mechanisms used to dissociate, or "prune," branched filaments has remained limited. Glia maturation factor (GMF) is a cofilin family protein that binds to the Arp2/3 complex and catalyzes branch dissociation. Here, we show that another ligand of Arp2/3 complex, Saccharomyces cerevisiae coronin (Crn1), enhances Gmf1-mediated debranching by 8- to 10-fold, and that these effects depend on Arp2/3-binding "C" and "A" motifs in Crn1. Further, we show that Crn1 directly binds with high affinity (K