D. Rathore et Tf. Mccutchan, Role of cysteines in Plasmodium falciparum circumsporozoite protein: Interactions with heparin can rejuvenate inactive protein mutants, P NAS US, 97(15), 2000, pp. 8530-8535
Citations number
27
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Various pathogenic bacteria, viruses, and protozoan bind to glycosaminoglyc
an-based receptors on host cells and initiate an infection. Sporozoites of
Plasmodium predominantly express circumsporozoite (CS) protein on their sur
face, which binds to heparan sulfate proteoglycans on liver cell surface th
at subsequently leads to malaria. Here we show that the interaction of free
heparin with this parasite ligand has the potential to be a critical compo
nent of invasion. CS protein of P. falciparum contains four cysteines at po
sitions 361. 365, 396. and 401. In this study, all four cysteine residues w
ere mutagenized to alanine both individually and in different combinations.
Conversion of cysteine 396 to alanine (protein CS3) led to a 10-fold incre
ase in the binding activity of the protein to HepG2 cells. Replacement of c
ysteines at positions 361, 365. and 401 either alone or in different combin
ations led to a near total loss of binding. Surprisingly, activity in these
inactive mutants could be effectively restored in the presence of submolar
concentrations of heparin. Heparin also up-regulated binding of CS3 at sub
molar concentrations with respect to the protein but downregulated binding
when present in excess. Given the significantly different concentrations of
heparin in different organs of the host and the in vitro results described
here one can consider in vivo ramifications of this phenomenon for pathoge
n targeting of specific organs and for the functional effects of antigenic
variation on receptor ligand interaction.