title: The Plasmodium falciparum schizont phosphoproteome reveals extensive phosphatidylinositol and cAMP-protein kinase A signaling.
abstract: The asexual blood stages of  Plasmodium falciparum  cause the most lethal form of human malaria. During growth within an infected red blood cell, parasite multiplication and formation of invasive merozoites is called schizogony. Here, we present a detailed analysis of the phosphoproteome of P. falciparum schizonts revealing 2541 unique phosphorylation sites, including 871 novel sites. Prominent roles for cAMP-dependent protein kinase A- and phosphatidylinositol-signaling were identified following analysis by functional enrichment, phosphoprotein interaction network clustering and phospho-motif identification tools. We observed that most key enzymes in the inositol pathway are phosphorylated, which strongly suggests additional levels of regulation and crosstalk with other protein kinases that coregulate different biological processes. A distinct pattern of phosphorylation of proteins involved in merozoite egress and red blood cell invasion was noted. The analyses also revealed that cAMP-PKA signaling is implicated in a wide variety of processes including motility. We verified this finding experimentally using an in vitro kinase assay and identified three novel PKA substrates associated with the glideosome motor complex: myosin A, GAP45 and CDPK1. Therefore, in addition to an established role for CDPK1 in the motor complex, this study reveals the coinvolvement of PKA, further implicating cAMP as an important regulator of host cell invasion.
authors.affiliation: Centre for Molecular and Biomolecular Informatics, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands. e.lasonder@ncmls.ru.nl
authors.forename: Edwin
authors.initials: E
authors.lastname: Lasonder
authors.forename: Judith L
authors.initials: JL
authors.lastname: Green
authors.forename: Grazia
authors.initials: G
authors.lastname: Camarda
authors.forename: Hana
authors.initials: H
authors.lastname: Talabani
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Holder
authors.forename: Gordon
authors.initials: G
authors.lastname: Langsley
authors.forename: Pietro
authors.initials: P
authors.lastname: Alano
mesh_terms: D000818:Animals; D002853:Chromatography, Liquid; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D010716:Phosphatidylinositols / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010963:Plasmodium falciparum / Q000378:metabolism*; D020543:Proteome; D015800:Protozoan Proteins / Q000378:metabolism*; D015398:Signal Transduction; D053719:Tandem Mass Spectrometry
chemical_list: D010716:Phosphatidylinositols; D010750:Phosphoproteins; D020543:Proteome; D015800:Protozoan Proteins; D017868:Cyclic AMP-Dependent Protein Kinases