Das Neves Guevara Diaz, SA; (2014) Protein Interactions in the Plasmodium falciparum Merozoite Motor Complex. Doctoral thesis , UCL ( University College London).

Abstract

The actomyosin motor that drives both motility and host cell invasion in the human malaria parasite Plasmodium falciparum is thought to be coupled through aldolase to the cytoplasmic domain (CTD) of type 1 membrane proteins of the thrombospondin-related anonymous protein (TRAP) family. Other type 1 membrane proteins including apical membrane antigen (AMA1) and members of the erythrocyte binding antigen (EBL) and reticulocyte binding homologue (Rh) protein families have been implicated in host cell binding and moving junction formation. We show that P. falciparum aldolase binds to P. falciparum actin. Using a kinetic assay, we show that TRAP family members also bind to aldolase. A direct binding method confirmed that merozoite TRAP (MTRAP) and TRAP bind aldolase and indicated that the interaction is mediated by more than just the C-terminal six amino acid residues identified previously. Single amino acid substitutions in the CTD abolished binding to aldolase. MTRAP CTD was phosphorylated by calcium dependent protein kinase 1 (CDPK1) and protein kinase A, kinases that are known to phosphorylate other motor proteins, and this modification increased the affinity of binding ten-fold. Similarly AMA1, EBA and Rh protein families also bound to aldolase, with the affinity also increased by CTD phosphorylation. Therefore other proteins involved in host cell recognition and invasion, in addition to members of the TRAP family, may be connected to the motor through aldolase. If this is the case their affinity for aldolase may also be important in addition to their host ligand specificity in determining the use of, and efficiency of alternate invasion pathways. These interactions also contributed to stimulate actin polymerization and enhance aldolase enzymatic activity, increasing the enzyme affinity for it’s substrate, and potentially to the compartmentalization of the glycolytic pathway and consequent ATP availability for motor complex function.

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