Identification of Reticulocyte Binding Domain of Plasmodium ovale curtisi Duffy Binding Protein (PocDBP) Involved in Reticulocyte Invasion

Abstract

The <i>Plasmodium ovale curtisi</i> (Poc) prevalence has increased substantially in sub-Saharan African countries as well as regions of Southeast Asia. Poc parasite biology has not been explored much to date; in particular, the invasion mechanism of this malaria parasite remains unclear. In this study, the binding domain of the Duffy binding protein of <i>P. ovale curtisi</i> (PocDBP) was characterized as an important ligand for reticulocyte invasion. The homologous region of the <i>P. vivax</i> Duffy binding protein in PocDBP, named PocDBP-RII herein, was selected, and the recombinant PocDBP-RII protein was expressed in an <i>Escherichia coli</i> system. This was used to analyze reticulocyte binding activity using fluorescence-activated cell sorting and immune serum production in rabbits. The binding specificity was proven by treating reticulocytes with trypsin, chymotrypsin and neuraminidase. The amino acid sequence homology in the N-terminal Cys-rich region was found to be ~ 44% between PvDBP and PocDBP. The reticulocyte binding activity of PocDBP-RII was significantly higher than the erythrocyte binding activity and was concentration dependent. Erythrocyte binding was reduced significantly by chymotrypsin treatment and inhibited by an anti-PocDBP-RII antibody. This finding suggests that PocDBP may be an important ligand in the reticulocyte invasion process of <i>P. ovale curtisi.</i>