Plasmodium falciparum, the major causative agent of human
malaria, is an
Apicomplexa protozoan parasite which invades in its
intermediate host hepatocytes and
erythrocytes. The
driving force underlying internalization into the
host cell is thought to involve both
polymerization of
parasite actin, as entry is inhibited by the
cytochalasins, and an
actin motor-associated protein. In the related
Apicomplexa parasite,
Toxoplasma gondii, the involvement of
parasite actin during both processes of motility and
host cell entry has been
genetically established. In a search for molecules that can regulate
actin dynamics within
Apicomplexa parasites, we have identified a P.
falciparum homologue of the
actin associated protein called
coronin originally described in the
amoeba Dictyostelium discoideum. The single copy gene displays a strong homology with the
amoeba sequence and with the bovine and human
coronin homologues recently
cloned. This homology lies not only within the
N-terminus containing the five WD repeats that characterize
coronin but also extends in the
C-terminal part. Furthermore, using an affinity-purified
mouse monoclonal antibody against D. discoideum
coronin, we have detected in extracts of P.
falciparum young and mature
schizonts a 42-kDa
polypeptide which binds this
antibody and is present in a Triton
insoluble fraction that also contains
parasite actin filaments. In addition, the
recombinant protein encoded by the homologue nucleotidic sequence of P.
falciparum coronin is indeed recognized by the
antibody against D. discoideum
coronin. Finally, the cross-reactive
polypeptide displays the ability to cosediment with exogenous
F-actin, a property which fits with its involvement in
actin dynamics.
