Cryo-electron microscopy structures of pyrene-labeled ADP-Pi- and ADP-actin filaments

Abstract

We report high resolution cryo-electron microscopy structures of actin filaments with N-1-pyrene conjugated to cysteine 374 and either ADP (3.2 [A]) or ADP-phosphate (3.0 [A]) in the active site. Polymerization buries pyrene in a hydrophobic cavity between subunits along the long-pitch helix with only minor differences in conformation compared with native actin filaments. These structures explain how polymerization increases the fluorescence 20-fold, how myosin and cofilin binding to filaments reduces the fluorescence and how profilin binding to actin monomers increases the fluorescence.