Molecular cloning, expression, and characterization of a novel human serine/threonine protein phosphatase, PP7, that is homologous to Drosophila retinal degeneration C gene product (rdgC).
A novel serine/threonine protein phosphatase (PPase) designated PP7 was identified from cDNA produced from human retina RNA. PP7 has a molecular mass of approximately 75 kDa, and the deduced amino acid sequence of PP7 contains a phosphatase catalytic core domain that possesses all of the invariant motifs of the PP1, PP2A, PP2B, PP4, PP5, and PP6 gene family. However, PP7 has unique N- and C-terminal regions and shares < 35% identity with the other known PPases. The unique C-terminal region of PP7 contains multiple Ca2+ binding sites (i.e. EF-hand motifs). This region of PP7 is similar to the Drosophila retinal degeneration C gene product (rdgC), and PP7 and rdgC share 42.1% identity. Unlike the other known PPases, the expression of PP7 is not ubiquitous; PP7 was only detected in retina and retinal-derived Y-79 retinoblastoma cells. Expression of recombinant human PP7 in baculovirus-infected SF21 insect cells produces an active soluble enzyme that is capable of utilizing phosphohistone and p-nitrophenyl phosphate as substrates. The activity of recombinant PP7 is dependent on Mg2+ and is activated by calcium (IC50 approximately equal to 250 microM). PP7 is not affected by calmodulin and is insensitive to inhibition by okadaic acid, microcystin-LR, calyculin A, and cantharidin.
Huang
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Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, Mobile 36688, USA.
Honkanen
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D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004330:Drosophila; D029721:Drosophila Proteins; D006801:Humans; D008274:Magnesium / Q000378:metabolism; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000378:metabolism; D012162:Retinal Degeneration; D018411:Spodoptera; D014407:Tumor Cells, Cultured
D002135:Calcium-Binding Proteins; D029721:Drosophila Proteins; C107424:PPEF1 protein, human; D010749:Phosphoprotein Phosphatases; C074643:rdgC protein, Drosophila; D008274:Magnesium