Plasmodium falciparum histidine-rich protein II binds to actin, phosphatidylinositol 4,5-bisphosphate and erythrocyte ghosts in a pH-dependent manner and undergoes coil-to-helix transitions in anionic micelles.
The recombinant histidine-rich protein II (HRPII) from Plasmodium falciparum was shown to bind actin and phosphatidylinositol 4,5-bisphosphate (PIP(2)) in vitro in a pH-dependent manner, very similar to hisactophilin, an actin-binding protein from ameba. Binding of HRPII to actin and PIP(2) occurred at pH 6.0 and 6.5, but not above pH 7.0. Circular dichroism (CD) spectroscopy confirmed that HRPII interacts with actin at pH below 7.0, as judged by the changes induced in the secondary structure of the HRPII/actin mixture. Further CD analysis demonstrated that HRPII adopts a predominantly alpha-helical conformation with anionic micelles of PIP(2) and SDS, but not with neutral micelles of phosphatidylcholine (PC), a feature that is common to many actin-binding proteins involved in cytoskeleton remodeling. Similarly to hisactophilin, a GFP-HRPII fusion protein shuttled from the cytoplasm to the nucleus of HeLa cells as the cellular pH was lowered from 8.0 to 6.0. HeLa cells transfected with the HRPII gene showed increased levels of histidine-rich proteins (HRPs) in the soluble cell fraction at pH 8.0. At pH 6.0, however, HRPs were detected mainly in the insoluble cell fraction. Interestingly, we found that HRPII binds to human erythrocyte membranes at pH 6.0 and 6.5 but not at pH above 7.0. Our results point to remarkable similarities between HRPII, hisactophilin, and actin-binding proteins. Possible roles of the HRPII during Plasmodium infection are discussed in the light of these findings.
Benedetti
Celso Eduardo
CE
Centro de Biologia Molecular Estrutural (CEBIME), Laboratório Nacional de Luz Sincrotron (LNLS), CP6192, Campinas, SP CEP 13084-971, Brazil. celso@lnls.br
Kobarg
Jörg
J
Pertinhez
Thelma Aguiar
TA
Gatti
Reynaldo Mascagni
RM
de Souza
Osmar Norberto
ON
Spisni
Alberto
A
Meneghini
Rogério
R
D000199:Actins / Q000378:metabolism*; D000818:Animals; D000838:Anions / Q000737:chemistry; D001665:Binding Sites; D002467:Cell Nucleus / Q000502:physiology; D003599:Cytoskeleton / Q000502:physiology; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008823:Micelles; D010713:Phosphatidylcholines / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D010963:Plasmodium falciparum / Q000166:cytology / Q000378:metabolism*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D021381:Protein Transport / Q000502:physiology; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism*; D000099053:Histidine-Rich Glycoprotein
D000199:Actins; D000838:Anions; D008823:Micelles; D010713:Phosphatidylcholines; D019269:Phosphatidylinositol 4,5-Diphosphate; D011506:Proteins; D015800:Protozoan Proteins; D000099053:Histidine-Rich Glycoprotein