Sequence diversity and antigenic polymorphism in the Plasmodium yoelii p235 high molecular mass rhoptry proteins and their genes

A gene family in Plasmodium yoelii YM encodes p235. a group of high molecul ar mass erythrocyte-binding rhoptry proteins. Sequence analysis of 6 cDNA c lones from the 3' end of expressed p235 genes divided them into two groups corresponding to genes on chromosomes 1, and 5 acid 6, respectively. Twelve partial p235 protein sequences, derived from cDNA sequences from the regio n with greatest protein sequence similarity to Plasmodium vivax RBP2, fell into three groups, together with one chimeric sequence. A comparison of the se cDNA sequences with genomic DNA sequences from the same region suggested that only a subset of the gene repertoire is expressed. Three genomic DNA clones, derived from the 5' end of p235 genes designated EI, E2 and E5 and located on chromosome 5/6, were also obtained and aligned with sequences fr om the known E8 and E3 genes. In the region of overlap there was only simil ar to 27% protein sequence identity, indicating that the sequences in this p235 N-terminal region are more diverse than at the C-terminal end. This se quence variation in the expressed genes did not result in antigenically dif ferent rhoptry proteins as detected with a panel of p235-specific mAbs. Onl y one schizont out of 500 examined with mAb 25.86 appeared to be an antigen ic variant, with all of the developing merozoites in this schizont bring mA b 25.86 negative. No other antigenic variants were detected with the other antibodies, and therefore it is likely that these antibodies recognise cons erved epitopes. (C) 2001 Elsevier Science B.V. All rights reserved.