Structural insight into regulation of myosin phosphatase by CPI‐17

• Published in: The FASEB journal 2007-04, Vol.21 (5), p.A520-A520
• Main Authors: Eto, Masumi, Kitazawa, Toshio, Matsuzawa, Fumiko, Aikawa, Sei‐ichi, Kirkbride, Jason A, Isozumi, Noriyoshi, Nishimura, Yumi, Brautigan, David L, Ohki, Shin‐ya
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.21.5.A520

Cellular activity of type‐1 Ser/Thr phosphatase (PP1) is controlled by endogenous phospho‐inhibitor proteins, which transduce kinase signals into PP1. Inhibition of myosin phosphatase, a PP1 holoenzyme, by a specific inhibitor protein CPI‐17 is required for a robust smooth muscle contraction, long‐term synaptic depression, and cell transformation. In response to G‐protein‐mediated signaling, phosphorylation of CPI‐17 at Thr38 triggers a > 1000‐fold increase of inhibitory potency. However, mechanisms for phospho‐inhibitor‐mediated inhibition of PP1 have yet to be elucidated. We solved the NMR structure of phospho‐CPI‐17 (P‐CPI‐17), which reveals how phosphorylation triggers a conformational change to convert the protein into a potent inhibitor for myosin phosphatase. Upon phosphorylation, P‐Thr38 is moved 8.1 Å to solvent, and two pairs of helices undergo re‐alignment into parallel. This helix re‐alignment results in the formation of a hydrophobic core of intercalated side‐chains that is needed for the potent inhibition of myosin phosphatase. Thus, the profound change in potency of CPI‐17 arises from phosphorylation, conformational change and hydrophobic stabilization of a rigid structure. Furthermore, a computer model predicts multisite interactions with myosin phosphatase, which account for the specificity of CPI‐17.