Fig. 3. Model of the pointed end.
(A) Domain diagram of Tmod (according to Fig. 1A), showing a secondary structure prediction of the N-terminal region by several algorithms (15). The prediction suggests that the two TM-binding sites, which are similar in size, also share a similar fold, consisting of a three-helix bundle. (B) Model of the pointed end, with the structures of the complexes of actin with ABS1 and ABS2 (magenta) superimposed onto the first two protomers of the filament (marine and blue). ABS2 also contacts the third protomer (purple-colored area). TM is shown in the stable “blocked” position, which it assumes when bound alone to the filament (23). A tentative model of the two TM-binding sites of Tmod (green), based on the results of the secondary structure prediction and energy minimization (15), is shown for reference (see also movie S4).