Fig. 5: Structural models for the dynamics of G-actin.
From: Bound nucleotide can control the dynamic architecture of monomeric actin
In each panel the left column schematically depicts a potential structural mechanism to explain the observed dynamics (T and D indicate ATP- and ADP-bound actin ground states, respectively, and T* and D* indicate the respective excited states), the middle panels plot various ground- and excited-state chemical shifts against each other, and the right column depicts the mechanistic conclusion from the data (see main text). In the middle column, each datapoint represents an isoleucine residue. Residues with different ground-state chemical shifts in ATP- and ADP-actin are boxed, and are not used to make structural comparisons. a, Model in which actin exists in only two conformational states, which are differentially biased by ATP and ADP (left). In such a model, T and D* are conformationally identical and have the same chemical shifts, as do D and T*. The scatter plots (middle) compare the ATP and ADP* 13C chemical shifts (top) and the ADP and ATP* chemical shifts (bottom). Off-diagonal, non-boxed points indicate structural differences between the states (more definitive for the T*/D comparison than the T/D* comparison), ruling out a two-state equilibrium (right). b, In a three-state model, ATP- and ADP-actin have distinct ground-state structures, but populate a common excited state (left). The scatter plot of ATP* versus ADP* 13C chemical shifts (middle) shows numerous off-diagonal, non-boxed points, indicating the two forms do not populate a common excited state (right). c, In a four-state equilibrium, ATP- and ADP-actin have distinct ground- and excited-state conformations (left). The scatter plots (middle) of ATP* versus ADP* (top) and ATP versus ADP (bottom) 13C chemical shifts show numerous off-diagonal, non-boxed points, indicating four distinct conformations (right).
