Fig. 2: The I3:PP1 holoenzyme.

A The structure of I3 when bound to PP1; residues shown as sticks and labeled. PP1 motif residue labels are colored as in (1A). I3 residues not modeled due to a lack of electron density indicated by dashed lines in yellow hues. B The I3:PP1 complex with I3 shown as yellow sticks and PP1 shown as a surface colored according to electrostatic potential. The location of acidic patch 2 is indicated. I3 residues not modeled due to a lack of electron density indicated by dashed lines in yellow hues. C Close up of PP1 acidic patch 2. PP1 acidic residues shown as sticks and labeled (gray) with I3 residues shown as sticks (yellow). Electrostatic/polar interactions indicated by black dotted lines. Dynamic I3 residues^{31,32,33,34,35,36,37} indicated by dashed lines in yellow hues. D The I3 ‘kink’. PP1 shown as a transparent gray surface with I3 shown as sticks in yellow; the I3 caspase cleavage sequence, ⁴⁶DTVD⁴⁹, is colored slightly darker yellow for clarity. Electrostatic/polar interactions that stabilize the kink and DTVD residues shown as dashed black lines. E Same as B with the I3:PP1 complex rotated by 180° to view the C-terminal portion of I3 bound to PP1. PP1 acidic patch 1, also known as the PP1 acidic substrate binding groove, is labeled. F Close-up of PP1 acidic patch 1. PP1 acidic residues shown as sticks and labeled (gray) with I3 residues shown as sticks (yellow). Electrostatic/polar interactions indicated by dashed black lines. Distances between the Cys60 sulfur atom and the PP1 M1, M2 metals indicated by magenta dotted lines with the distances labeled.