Nucleotide sequence polymorphism in region I of the gene encoding erythrocyte binding-like protein, ebl-1 in Kenyan plasmodium falciparum field isolates
Malaria is a major health challenge facing Africa where it kills one child every 30 seconds. A vaccine is the ideal long-term solution for resource poor countries but there is as yet no . effective vaccine. Several merozoite surface proteins have been proposed as vaccine candidates and highly polymorphic regions have been observed within the genes coding for these proteins. The erythrocyte binding protein family, of which ebl-l is a member, encodes antigenic surface proteins that normally become recognised by the host immune system, and polymorphism observed in these genes is likely driven by immune pressure. This study investigated the level of polymorphism in region I of the ebl-l gene using the molecular population genetics approach. Plasmodium Jalciparum-infected blood samples were obtained from four malaria endemic regions of Kenya. These were Kilifi, Kisumu, Embu and Busia from which 23, 6, 5 and 3 samples were collected respectively. Total genomic DNA was extracted from these samples and gene-specific primers were used to amplify region I of the ebl-I gene. The nucleotide sequences of the amplified products were obtained. Several neutrality tests were applied on the DNA sequences of region I of the ebl-l gene from 37 field isolates. All the tests revealed that region I is under positive Darwinian selection acting to promote diversity at the amino acid level. These results suggest that region I of the ebl-l is under positive selection, presumably exerted by the host immune system. However, a 5 nucleotides frame shift insertion observed in the majority of the field isolates (84%), which, effectively knock-out the gene, suggests that this gene may not be an appropriate vaccine candidate.