Characterization of a protein of the rodent malarial parasite Plasmodium chabaudi containing a novel leucine-histidine zipper

Clones from cDNA and genomic DNA libraries of Plasmodium chabaudi 96V covering the entire open reading frame for a yet uncharacterized malarial protein were isolated Counting the first ATG as start codon the intronless gene codes for a 229 kDa protein. In the centre of the protein a 364 amino add repeat region is located and is based on 32 11-mer repeats divided by two 6-mer repeats into three blocks.Modelling of the repeat region led us to propose a model where each of the three units forms an a-helical coiled-coil triple-helix containing a novel leucine-histidine zipper. Each unit resembles in structure the units present in spectrin molecules. The repeat region is flanked by predicted heptad based a-helical coiled-coil regions and the 229 kDa protein has an overall character of a cytoskeletal protein.Antisera raised against recombinant polypeptides from two different regions of the 229 kDa protein reacted in western-blotting experiments with a Mr 240 000/ 225 000 doublet present in protein extracts from P. chabaudi 96V. The same sera in immunofluorescence suggested a localization of the 229 kDa protein in the organelles of the apical complex, presumably in the rhoptry organelles, and an assodation of the 229 kDa protein with the erythrocyte membrane. Furthermore it was shown in westernblotting experiments with the recombinant polypqjtides that the 229 kDa protein is a natural immunogen during infection.We named the 229 kDa protein Rq>eated Organellar Protein (ROPE) and suggest that ROPE may be involved in the process of invasion, that it interacts with the erythrocyte cytoskeleton and that the leucine-histidine zipper may be involved in molecular mimicry of spectrin