title: Contractile protein system in the asexual stages of the malaria parasite Plasmodium falciparum.
abstract: F-actin was detected in asexual-stage Plasmodium falciparum parasites by fluorescence microscopy of blood films stained with fluorescent phalloidin derivatives. F-actin was present at all stages of development and appeared diffusely distributed in trophic parasites, but merozoites stained strongly at the poles and peripheries. No filament bundles could be discerned. A similar distribution was obtained by immunofluorescence with 2 polyclonal anti-actin antibodies, one of which was directed against a peptide sequence present only in parasite actin (as inferred from the DNA sequence of the gene). A monoclonal anti-actin antibody stained very mature or rupturing schizonts but not immature parasites. Myosin was identified in immunoblots of parasite protein extracts by several monoclonal anti-skeletal muscle myosin antibodies, as well as by a polyclonal antiserum directed against a consensus conserved myosin sequence (IQ motif). The identity of the polypeptides recognised by these antibodies was confirmed by overlaying blots with biotinylated F-actin. The antiserum and one of the monoclonal antibodies were used in immunofluorescence studies and were found to stain all blood-stage parasites, with maximal intensity towards the poles of merozoites. Our results are consistent with the presence of an actomyosin motor system in the blood-stage malaria parasite.
authors.affiliation: Department of Immunology, UMDS, Medical School, Guy's Hospital, London, UK.
authors.forename: S E
authors.initials: SE
authors.lastname: Webb
authors.forename: R E
authors.initials: RE
authors.lastname: Fowler
authors.forename: C
authors.initials: C
authors.lastname: O'Shaughnessy
authors.forename: J C
authors.initials: JC
authors.lastname: Pinder
authors.forename: A R
authors.initials: AR
authors.lastname: Dluzewski
authors.forename: W B
authors.initials: WB
authors.lastname: Gratzer
authors.forename: L H
authors.initials: LH
authors.lastname: Bannister
authors.forename: G H
authors.initials: GH
authors.lastname: Mitchell
mesh_terms: D000199:Actins / Q000032:analysis*; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000913:Antibodies, Protozoan; D006801:Humans; D008856:Microscopy, Fluorescence / Q000379:methods; D008969:Molecular Sequence Data; D009218:Myosins / Q000032:analysis*; D010963:Plasmodium falciparum / Q000737:chemistry* / Q000254:growth & development / Q000276:immunology; D015800:Protozoan Proteins / Q000032:analysis
chemical_list: D000199:Actins; D000911:Antibodies, Monoclonal; D000913:Antibodies, Protozoan; D015800:Protozoan Proteins; D009218:Myosins