EVALUATING ATOMIC MODELS OF F-ACTIN WITH AN UNDECAGOLD-TAGGED PHALLOIDIN DERIVATIVE

We have prepared an undecagold-tagged phalloidin derivative to determi ne this mushroom toxin's binding site and orientation within the F-act in filament by scanning transmission electron microscopy (STEM) and 3- D helical reconstruction. Remarkably, when stoichiometrically bound to F-actin, the undecagold moiety of the derivative could be directly vi sualized by STEM along the two half-staggered long-pitch helical stran ds of single filaments. Most importantly, the structural data obtained when combined with various biochemical constraints enabled us to crit ically evaluate two distinct atomic models of the F-actin filament (i. e. the Holmes-Lorenz versus the Schutt-Lindberg model). Taken together , our data are in excellent agreement with the Holmes-Lorenz model. (C ) 1998 Academic Press Limited.