FIGURE 2. Electrostatic surface representations of the PP1–MYPT1_1–299 complex.

a–c, Surfaces of PP1 (a), MYPT1 (b) and their complex (c) calculated using identical parameters (red and blue indicate regions charged negatively and positively, respectively). The Y-shaped catalytic cleft of PP1 is composed of three grooves: hydrophobic, acidic and C-terminal. The 12–13 loop separates the acidic and the C-terminal grooves. The reshaping of the catalytic cleft of PP1 results from the binding of the N terminus of MYPT1 near the hydrophobic groove and the addition of the acidic cleft of the ankyrin repeats at the other end of the cleft. d, Sequences of the RLC around Ser 19 and the MYPT1 around the regulatory phosphorylation sites Thr 695 and Thr 850. Note the existing charge complementarity between these sequences and the catalytic cleft of myosin phosphatase.