Genetic characterisation of the erythrocyte-binding protein ($$\hbox {Pk}{\upbeta }\hbox {II}$$) of Plasmodium knowlesi isolates from Malaysia

Abstract

Plasmodium knowlesi contributes to the majority of human malaria incidences in Malaysia. Its uncontrollable passage among the natural monkey hosts can potentially lead to zoonotic outbreaks. The merozoite of this parasite invades host erythrocytes through interaction between its erythrocyte-binding proteins (EBPs) and their respective receptor on the erythrocytes. The region II of P. knowlesi EBP, P. knowlesi beta ( $$\hbox {Pk}{\upbeta }\hbox {II}$$ ) protein is found to be mediating merozoite invasion into monkey erythrocytes by interacting with sialic acid receptors. Hence, the objective of this study was to investigate the genetic diversity, natural selection and haplotype grouping of $$\hbox {Pk}{\upbeta }\hbox {II}$$ of P. knowlesi isolates in Malaysia. Polymerase chain reaction amplifications of $$\hbox {Pk}{\upbeta }\hbox {II}$$ were performed on archived blood samples from Malaysia and 64 $$\hbox {Pk}{\upbeta }\hbox {II}$$ sequences were obtained. Sequence analysis revealed length polymorphism, and its amino acids at critical residues indicate the ability of $$\hbox {Pk}{\upbeta }\hbox {II}$$ to mediate P. knowlesi invasion into monkey erythrocytes. Low genetic diversity ( $${\uppi } = 0.007$$ ) was observed in the $$\hbox {Pk}{\upbeta }\hbox {II}$$ of Malaysia Borneo compared to Peninsular Malaysia ( $${\uppi } = 0.015$$ ). The $$\hbox {Pk}{\upbeta }\hbox {II}$$ was found to be under strong purifying selection to retain infectivity in monkeys and it plays a limited role in the zoonotic potential of P. knowlesi. Its haplotypes could be clustered into Peninsular Malaysia and Malaysia Borneo groups, indicating the existence of two distinct P. knowlesi parasites in Malaysia as reported in an earlier study.