SRA

Plasmodium knowlesi is a malaria parasite commonly found in macaques, and the causative agent of severe zoonotic disease in South East Asia. Whilst P. knowlesi can be readily adapted to in vitro culture with macaque red blood cells (RBC), extended adaptation and improved invasion efficiency are required to maintain the parasite in human RBC. In all malaria parasite species, two families of adhesins, the reticulocyte binding like/reticulocyte binding homologue (RBL/RH) protein and Duffy binding protein/erythrocyte binding antigen (DBP/EBA) are secreted onto the merozoite surface and bind to specific host cell receptors to facilitate RBC invasion. These proteins are important determinants of parasite virulence and host cell tropism, and are potential vaccine candidates. Here we provide the first de novo genome assembly of a human-adapted parasite, representing an important P. knowlesi reference line, and compare it with similar cynomolgus-adapted lines. Comparison of the genome sequences of three parasite lines generated during adaptation, highlight a role for an RBL protein called normocyte binding protein Xa (NBPXa) in human RBC invasion. By generating a parasite line with the NBPXa gene disrupted we show that this protein is required for invasion of human but not macaque RBC. This finding has clear implications for understanding disease severity and the potential for human to human transmission. It provides a robust experimental platform to unravel conserved malaria parasite invasion mechanisms, and in particular provides the basis for intervention strategies to control P. knowlesi and related parasites such as the major human pathogen Plasmodium vivax.