Cloning and in vitro expression of TPK3, a Toxoplasma gondii homologue of shaggy/glycogen synthase kinase-3 kinases.
As an initial effort to dissect the signaling pathways responsible for pathogenesis of Toxoplasma gondii infection, we report the cloning and in vitro functional studies of TPK3 (Toxoplasma protein kinase-3), a homologue of shaggy/glycogen synthase kinase-3 (GSK-3) kinases. The shaggy/GSK-3 family of kinases are highly conserved protein kinases that play important roles in cell fate determination, nuclear signaling and hormonal regulation. The TPK3 gene was isolated by RT-PCR with degenerate primers corresponding to highly conserved regions of serine/threonine protein kinases. The complete sequences of genomic and cDNA clones indicated the open reading frame, 1185 bp in size, is interrupted by five introns. The predicted protein sequence of TPK3 shows 54% identity to shaggy/GSK-3 over the catalytic domains. Southern analysis revealed TPK3 is a single copy locus in the Toxoplasma genome. Antisera to other GSK-3 proteins from other species recognized GST-TPK3 and a protein of the predicted size in parasites lysates. In vitro kinase assays with GST-TPK3 indicated that TPK3 autophosphorylates and phosphorylates protein phosphatase inhibitor-2 (I-2), a specific substrate of GSK-3 kinase.
Qin
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Department of Medicine (Division of Infectious Diseases), Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Tang
J
J
Kim
K
K
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary; D029721:Drosophila Proteins; D015870:Gene Expression; D017125:Genes, Protozoan; D038362:Glycogen Synthase Kinase 3; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013379:Substrate Specificity; D014122:Toxoplasma / Q000201:enzymology / Q000235:genetics*
D018076:DNA, Complementary; D029721:Drosophila Proteins; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; D017346:Protein Serine-Threonine Kinases; C080335:Sgg protein, Drosophila; C114247:TPK3 kinase protein, Toxoplasma; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3