Interaction of Smooth Muscle Myosin Phosphatase with Phospholipids
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- 作者：Masaaki Ito ; Jianhua Feng ; Shiho Tsujino ; Naoyuki Inagaki ; Masaki Inagaki ; Junko Tanaka ; Kazuhito Ichikawa ; David J. Hartshorne ; and Takeshi Nakano
- 刊名：Biochemistry
- 出版年：1997
- 出版时间：June 17, 1997
- 年：1997
- 卷：36
- 期：24
- 页码：7607 - 7614
- 全文大小：271K
- 年卷期：v.36,no.24(June 17, 1997)
- ISSN：1520-4995
文摘
The 130 kDa myosin-binding subunit (MBS) of smooth muscle myosinphosphatase wasdetected in cytoskeletal, cytosolic, and membrane fractions of T24cells. Also, MBS was distributedbetween cytoplasm and plasmalemma in mitotic REF52 cells. Theseobservations prompted this study ofthe interaction(s) of phospholipids with myosin phosphatase.Using a sedimentation assay, gizzard myosinphosphatase bound to vesicles of acidic phospholipids, i.e.phosphatidylserine (PS), phosphatidylinositol,and phosphatidic acid (PA). Neutral phospholipids did not bind.Binding of PS to myosin phosphatasealso was demonstrated by electrophoresis under nondenaturingconditions. Preferential binding of PA,compared to that of the other acidic phospholipids, was indicated.Interaction of acidic phospholipidswith myosin phosphatase inhibited phosphatase activity towardphosphorylated myosin. The extent ofPS binding with myosin phosphatase decreased on increasing ionicstrength and Mg2+ concentration.MBS (M130/M133) and M20 were phosphorylated by protein kinase A to3 and 1 mol of P/(mol ofsubunit), respectively. Phosphorylation of the holoenzymedecreased phospholipid binding with recoveryof phosphatase activity. Using limited proteolysis of theholoenzyme and various mutants, it was shownthat phospholipid binding was associated with the C-terminal part ofMBS, Ser 667-Ile 1004, and M20.The phosphorylation site involved in regulation of phospholipidbinding is within the C-terminal MBSsequence. These results suggest that myosin phosphatase mayinteract with membranes and thatphosphorylation by protein kinase A could modify this interaction.This mechanism could be importantin localization of myosin phosphatase and in targeting substrates atdifferent loci.