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First published online 24 April 2007
doi: 10.1242/jcs.007641

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F-actin binding is essential for coronin 1B function in vivo

¹ Lineberger Comprehensive Cancer Center and Department of Cell & Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-7295, USA
² Department of Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-7295, USA

^* Author for correspondence (e-mail: jbear{at}email.unc.edu)

Accepted 2 April 2007

Coronins are conserved F-actin binding proteins that have been implicated in a variety of processes including fibroblast migration, phagocytosis, and chemotaxis. Recent data from our lab indicate that coronin 1B coordinates Arp2/3-dependent actin filament nucleation and cofilin-mediated filament turnover at the leading edge of migrating fibroblasts. Analysis of coronin function has been hampered by the lack of a clear understanding of how coronin interacts with F-actin. Here, we identify a surface-exposed conserved arginine residue at position 30 (R30), which is crucial for coronin 1B binding to F-actin both in vitro and in vivo. Using actin co-sedimentation, we demonstrate that coronin 1B binds with high affinity to ATP/ADP-P_i–F-actin (170 nM) and with 47-fold lower affinity to ADP–F-actin (8 µM). In contrast to a previous study, we find no evidence for enhanced cofilin binding to F-actin in the presence of either coronin 1B or coronin 1A. Instead, we find that coronin 1B protects actin filaments from cofilin-induced depolymerization. Consistent with an important role for interactions between coronin 1B and F-actin in vivo, an R30D coronin mutant that does not bind F-actin localizes inefficiently to the leading edge. Furthermore, our analysis indicates that F-actin binding is absolutely required for coronin 1B to exert its effects on whole-cell motility and lamellipodial dynamics.

Key words: Coronin, Actin, Cofilin, Arp2/3, FRAP

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