SEARCH

SEARCH BY CITATION

Keywords:

  • myosin phosphatase;
  • protein phosphatase-1;
  • myosin phosphatase target subunit-1;
  • surface plasmon resonance

The interactions of the catalytic subunit of type 1 protein phosphatase (PP1c) and the N-terminal half (residues 1–511) of myosin phosphatase target subunit 1 (MYPT1) were studied. Biotinylated MYPT1 derivatives were immobilized on streptavidin-biosensor chips, and binding parameters with PP1c were determined by surface plasmon resonance (SPR). The affinity of binding of PP1c was: MYPT11–296 > MYPT11–38 > MYPT123–38. No binding was detected with MYPT11–34, suggesting a critical role for residues 35–38, i.e. the PP1c binding motif. Binding of residues 1–22 was inferred from: a higher affinity binding to PP1c for MYPT11–38 compared to MYPT123–38, as deduced from SPR kinetic data and ligand competition assays; and an activation of the myosin light chain phosphatase activity of PP1c by MYPT11–38, but not by MYPT123–38. Residues 40–296 (ankyrin repeats) in MYPT11–296 inhibited the phosphorylase phosphatase activity of PP1c (IC50 = 0.2 nm), whereas MYPT11–38, MYPT123–38 or MYPT11–34 were without effect. MYPT140–511, which alone did not bind to PP1c, showed facilitated binding to the complexes of PP1c–MYPT11–38 and PP1c–MYPT123–38. The inhibitory effect of MYPT140–511 on the phosphorylase phosphatase activity of PP1c also was increased in the presence of MYPT11–38. The binding of MYPT1304–511 to complexes of PP1c and MYPT11–38, or MYPT11–296, was detected by SPR. These results suggest that within the N-terminal half of MYPT1 there are at least four binding sites for PP1c. The essential interaction is with the PP1c-binding motif and the other interactions are facilitated in an ordered and cooperative manner.