Two functional reticulocyte binding-like (RBL) invasion ligands of zoonotic Plasmodium knowlesi exhibit differential adhesion to monkey and human erythrocytes

• Type of Material: Article
• Authors: Amma A. Semenya, Emory University; Tuan M Tran, Emory University; Esmeralda V S Meyer, Emory University; John W. Barnwell, Centers for Disease Control and Prevention; Mary R Galinski, Emory University
• Language: English
• Date: 2012-07-06
• Publisher: BioMed Central
• Publication Version: Final Published Version
• Copyright Statement: © 2012 Semenya et al.; licensee BioMed Central Ltd.
• License: Creative Commons Attribution 2.0 Generic
• Final Published Version (URL): http://www.malariajournal.com/content/11/1/228
• Title of Journal or Parent Work: Malaria Journal
• ISSN: 1475-2875
• Volume: 11
• Issue: 228
• Start Page: 1
• End Page: 12
• Grant/Funding Information: This research was funded by the National Institutes of Health, National Institute for Allergy and Infectious Diseases to MRG (1R01AI247 and R21AI094449).; The Yerkes National Primate Research Center received support from the National Center for Research Resources P51RR000165, and it is currently supported by the Office of Research Infrastructure Programs / OD P51OD011132.
• Research Categories: Health Sciences, Immunology

Abstract

Background Plasmodium knowlesi is a monkey malaria species that is becoming a serious public health concern infecting hundreds and perhaps thousands of humans in Southeast Asia. Invasion of erythrocytes by merozoites entails a cascade of molecular interactions. One step involves the adhesion of Plasmodium reticulocyte binding-like (RBL) proteins. Plasmodium knowlesi merozoites express only two RBL invasion ligands, known as Normocyte Binding Proteins (PkNBPXa and PkNBPXb). Methods Overlapping N-terminal regions of PkNBPXa and PkNBPXb were expressed in COS7 cells and tested for surface expression and adhesion to rhesus monkey erythrocytes. Subsequent tests to study specific receptor ligand interactions included adhesion to a panel of human and non-human primate erythrocytes, enzymatic treatment, and site directed mutagenesis. Results An N-terminal cysteine-rich region of PkNBPXb (PkNBPXb-II) exhibited specific adhesion to rhesus monkey erythrocytes. Mutation of four of five cysteines in PkNBPXb-II interfered with its surface expression on COS7 cells, suggesting disulphide bond conformation is critical for intracellular trafficking. Binding of PkNBPXb-II was abolished when rhesus erythrocytes were pre-treated with chymotrypsin, but not trypsin or neuraminidase. PkNBPXb-II also bound other Old World monkey species and gibbon erythrocytes. However, erythrocytes from other primate species including humans did not bind to PkNBPXb-II or native PkNBPXb. Importantly, unlike PkNBPXb, PkNBPXa bound human erythrocytes, and this binding was independent of the Duffy blood group determinant. Conclusions The data reported here begins to clarify the functional domains of the P. knowlesi RBLs. A binding domain has been identified and characterized in PkNBPXb. Notably, this study demonstrates that unlike PkNBPXb, PkNBPXa can bind to human erythrocytes, suggesting that PkNBPXa may function as a ligand to enable the invasion of P. knowlesi merozoites into human cells.