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 (OR F) for a Plasmodium chabaudi 96V protein were isolated. From the first ATG codon the intronless gene codes for a 229-kDa protein. Antisera r aised against recombinant polypeptides coded by two different regions of the gene reacted with a 240/225-kDa doublet on Western blots of par asite extracts. In immunofluorescence studies the same sera detected t he antigen at the apical end of the merozoite, possibly in rhoptry org anelles. In Western blotting experiments the recombinant polypeptides were recognised by antibodies induced by natural infection. A 364-amin o acid residue repetitive region, based on 32 11-mer repeats divided b y 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 t riple-helix containing a possible leucine-histidine zipper. Each unit resembles in structure the units present in spectrin. The repeat regio n is flanked by predicted heptad based alpha-helical coiled-coil regio ns, and we propose that the protein forms a dimer. The 229-kDa protein has the overall character of a cytoskeletal protein. We have named th e 229-kDa protein repetitive organellar protein (ROPE) and suggest tha t ROPE may be involved in the process of invasion, possibly by interac ting with the erythrocyte cytoskeleton, and that the leucine histidine -zipper may be involved in molecular mimicry of spectrin. (C) 1998 Els evier Science B.V. All rights reserved.