Plasmodium yoelii YM MAEBL protein is coexpressed and colocalizes with rhoptry proteins

We have previously cloned genes from multiple rodent malaria species exhibiting characteristics of the genes encoding Duffy binding like-erythrocyte binding proteins (DBL-EBP). Homology is seen in the intron/exon structure of the genes and in the carboxyl terminal region (including the deduced carboxyl cysteine-rich domain) of the proteins they encode. However, the amino termini of these proteins are not homologous to the DBL-EBP but contain tandem cysteine-rich regions that are similar to the cysteine-rich region of AMA-1 (apical membrane antigen-1), a rhoptry protein. This new family of proteins has been termed MAEBL and these are paralogues of both AMA-1 and the DBL-EBP. Serum against the carboxyl cysteine-rich region of the Plasmodium yoelii YM MAEBL reacted to parasites with a punctate fluorescence pattern characteristic of apical organelle proteins and also localized MAEBL to the surface of merozoites within schizonts. This antiserum immunoprecipitated a protein doublet (120/128 kDa) that was unexpectedly insoluble when compared to members of the DBL-EBP. Characterization of MAEBL was extended through colocalization studies comparing the P. yoelii YM MAEBL to other parasite proteins. This protein appeared to be located in the rhoptry organelles as it colocalized with both AMA-1 and the P. yoelii 235 kDa rhoptry proteins within parasites. In addition, MAEBL is expressed relatively early in schizont development and appears on the merozoite surface after segmentation. Both the pattern and time of expression of the P. yoelii YM MAEBL are consistent with a rhoptry rather than a microneme protein.