A Plasmodium chabaudi protein contains a repetitive region with a predicted spectrin-like structure

cDNA and genomic DNA clones covering the entire open reading frame (ORF) for a Plasmodium chabaudi 96V protein were isolated. From the first ATG codon the intronless gene codes for a 229-kDa protein. Antisera raised against recombinant polypeptides coded by two different regions of the gene reacted with a 240/225-kDa doublet on Western blots of parasite extracts. In immunofluorescence studies the same sera detected the antigen at the apical end of the merozoite, possibly in rhoptry organelles. In Western blotting experiments the recombinant polypeptides were recognised by antibodies induced by natural infection. A 364-amino acid residue repetitive region, based on 32 11-mer repeats divided by two 6-mer repeats into three blocks, is located in the centre of the protein. Analysis of this repetitive region led us to propose a model in which each of the three units forms an alpha-helical coiled-coil triple-helix containing a possible leucine-histidine zipper. Each unit resembles in structure the units present in spectrin. The repeat region is flanked by predicted heptad based alpha-helical coiled-coil regions, and we propose that the protein forms a dimer. The 229-kDa protein has the overall character of a cytoskeletal protein. We have named the 229-kDa protein repetitive organellar protein (ROPE) and suggest that ROPE may be involved in the process of invasion, possibly by interacting with the erythrocyte cytoskeleton, and that the leucine histidine-zipper may be involved in molecular mimicry of spectrin.