title: Exploiting the unique ATP-binding pocket of toxoplasma calcium-dependent protein kinase 1 to identify its substrates.
abstract: Apicomplexan parasites rely on calcium as a second messenger to regulate a variety of essential cellular processes. Calcium-dependent protein kinases (CDPK), which transduce these signals, are conserved among apicomplexans but absent from mammalian hosts, making them attractive targets for therapeutic intervention. Despite their importance, the signaling pathways CDPK regulate remain poorly characterized, and their protein substrates are completely unknown. In Toxoplasma gondii, CDPK1 is required for calcium-regulated secretion from micronemes, thereby controlling motility, invasion, and egress from host cells. CDPK1 is unique among parasite and mammalian kinases in containing glycine at the key "gatekeeper" residue, which results in an expanded ATP-binding pocket. In the present study, we use a synthetic ATPγS analogue that displays steric complementarity to the ATP-binding pocket and hence allows identification of protein substrates based on selective thiophosphorylation. The specificity of this approach was validated by the concordance between the identified phosphorylation sites and the in vitro substrate preference of CDPK1. We further demonstrate that the phosphorylation of predicted substrates is dependent on CDPK1 both in vivo and in vitro. This combined strategy for identifying the targets of specific protein kinases provides a platform for defining the roles of CDPKs in apicomplexans.
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine , 660 S. Euclid Ave., St. Louis, Missouri 63110, United States.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Lourido
authors.forename: Grace R
authors.initials: GR
authors.lastname: Jeschke
authors.forename: Benjamin E
authors.initials: BE
authors.lastname: Turk
authors.forename: L David
authors.initials: LD
authors.lastname: Sibley
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity; D014122:Toxoplasma / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D014123:Toxoplasmosis / Q000469:parasitology; D017871:Calcium-Calmodulin-Dependent Protein Kinases
chemical_list: D000255:Adenosine Triphosphate; D010455:Peptides; D010710:Phosphates; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C035638:thiophosphoric acid