Fig. 5. Model of the interaction between denatured actin and PFD. (A) Several views of the three-dimensional reconstruction of the PFD:actin complex in which the atomic model of unfolded actin generated upon its docking into the three-dimensional reconstruction of actin bound to nucleotide-free CCT (Llorca et al., 1999, 2000) has been fitted into the actin part of the PFD:actin complex. The envelope of the tips of the PFD:actin complex has been drawn as a yellow grid to allow visualization of the atomic model of unfolded actin. (B and C) Bottom and top views, respectively, of the tips of the tentacles of the atomic structure of the archaeal PFD from M.thermoautotrophicum (Siegert et al., 2000). (D and E) The same views of the structural model generated with human PFD subunits. In these images, the α and β archaeal subunits were used as templates, and the human α- and β-like subunits were placed in the center and outer positions, respectively. The β-like subunits are placed randomly. Human PFD was modeled using the homology modeling programs Swiss-PdbViewer and Swiss-Model (Guex and Peitsch, 1997; Schwede et al., 2000). In (C) and (E), the base of the structure and part of the tentacles have been removed to allow visualization of the outer surface of the tentacle tips. Surfaces (negatively charged residues in red, positively charged residues in blue) were generated using GRASP (Nicholls et al., 1991). (F) Several views of the modeled interaction between unfolded actin and PFD. The atomic structure of the archaeal PFD and the atomic model of unfolded actin shown in (A) were used as structures for the modeling of this interaction. Actin residues putatively involved in the interaction of PFD with CCT are highlighted as follows: residues involved in the interaction with CCT (Llorca et al., 2000, 2001b) (red); residues involved in PFD binding (Rommelaere et al., 2001) (yellow); residues involved in both functions (green).