ADPact: A versatile sensor for ADP-F-actin.

The dynamic organization of the actin cytoskeleton, crucial for numerous cellular processes, is intricately regulated by the nucleotide state of actin filaments (F-actin). Visualization tools for specifically detecting ADP-bound F-actin, however, remain limited. Here, we introduce ADPact, a 20-amino-acid peptide that selectively binds to ADP-F-actin. ADPact allows for the precise visualization of ADP-F-actin structures both in vitro and in eukaryotic cells, particularly under energy stress conditions where ADP-/ATP-actin ratio increases. Importantly, ADPact and its fluorescent fusion variant, ADPact-GFP, do not disrupt actin dynamics, ensuring accurate monitoring of cytoskeletal reorganization. Our findings provide a powerful tool for studying actin dynamics and offer fresh insights into the regulation of the cytoskeleton under physiological and pathological conditions.