Dual Ser and Thr phosphorylation of CPI-17, an inhibitor of myosin phosphatase, by MYPT-associated kinase

Phosphorylation of CPI-17 and PHI-1 by the MYPT1-associated kinase (M110 kinase) was investigated. M110 kinase is a recently identified serine/threonine kinase with a catalytic domain that is homologous to that of ZIP kinase (ZIPK, GST-rN-ZIPk, a constitutively active GST fusion fragment, phosphorylates CPI-17 (but not PHI-1) to a stoichiometry of 1.7 mol/mol, Phosphoamino acid analysis revealed phosphorylation of both Ser and Thr residues, Phosphorylation sites in CPI-17 were identified as Thr 38 and Ser 12 using Edman sequencing with P-32 release and a point mutant of Thr 38, (C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.