Fig. 2. Testing the interactions of Tmod at the pointed end by mutagenesis.
(A) Representation of the mutants studied here on a domain diagram of Tmod and on the structures of ABS1 and ABS2 superimposed onto the first two protomers (marine and blue) at the pointed end of the filament model (21) (see also movie S3). Residues mutated here are colored by atom type (carbon, yellow; oxygen, red; nitrogen, blue). Also shown are residues mutated in previous studies (green). Note that ABS1 only interacts with the first protomer, whereas ABS2 contacts the first three protomers of the filament. The third protomer is colored gray, except for the area that contacts ABS2, which is colored purple. (B) Normalized pointed end elongation rates of filament seeds as a function of Tmod concentration, with or without TM (conditions given on top). (C) Normalized pointed end elongation rates of filament seeds as a function of mutant Tmod concentration, and in the presence of TM (the individual titrations are shown in fig. S7). Each mutant is represented by a different color (keys are given on the bottom). (D) Comparison of the normalized pointed end elongation rates at 200 nM Tmod with or without (gray bars) TM.