Identification and characterization of a novel inositol polyphosphate 5-phosphatase.
We have identified a cDNA encoding a novel inositol polyphosphate 5-phosphatase. It contains two highly conserved catalytic motifs for 5-phosphatase, has a molecular mass of 51 kDa, and is ubiquitously expressed and especially abundant in skeletal muscle, heart, and kidney. We designated this 5-phosphatase as SKIP (Skeletal muscle and Kidney enriched Inositol Phosphatase). SKIP is a simple 5-phosphatase with no other motifs. Baculovirus-expressed recombinant SKIP protein exhibited 5-phosphatase activities toward inositol 1,4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate, phosphatidylinositol (PtdIns) 4,5-bisphosphate, and PtdIns 3,4, 5-trisphosphate but has 6-fold more substrate specificity for PtdIns 4,5-bisphosphate (K(m) = 180 microM) than for inositol 1,4, 5-trisphosphate (K(m) = 1.15 mM). The ectopic expression of SKIP protein in COS-7 cells and immunostaining of neuroblastoma N1E-115 cells revealed that SKIP is expressed in cytosol and that loss of actin stress fibers occurs where the SKIP protein is concentrated. These results imply that SKIP plays a negative role in regulating the actin cytoskeleton through hydrolyzing PtdIns 4,5-bisphosphate.
Ijuin
T
T
Department of Biochemistry, The Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
Mochizuki
Y
Y
Fukami
K
K
Funaki
M
M
Asano
T
T
Takenawa
T
T
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D019556:COS Cells; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000302:isolation & purification; D006801:Humans; D000072181:Inositol Polyphosphate 5-Phosphatases; D008969:Molecular Sequence Data; D010744:Phosphoric Monoester Hydrolases / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D011817:Rabbits; D013379:Substrate Specificity
D018076:DNA, Complementary; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases