MOLECULAR CHARACTERIZATION OF A PLASMODIUM-CHABAUDI ERYTHROCYTE MEMBRANE-ASSOCIATED PROTEIN WITH GLUTAMATE-RICH TANDEM REPEATS

The malarial parasite dramatically affects the structure and function of the erythrocyte membrane by exporting proteins that specifically in teract with the host membrane. This report describes the complete sequ ence and some biochemical properties of a 93-kDa Plasmodium chabaudi c habaudi protein that interacts with the host erythrocyte membrane. App roximately 40% of the deduced protein sequence consists of tandem repe als of 14 amino acids that are rich in glutamic acid residues. Compari son of the repeat sequences from two different P. c. chabaudi strains derived from the same initial isolate revealed an exact duplication of 294 nucleotides suggesting a recent unequal crossing-over event. Howe ver, in spite of this potentially high level of intragenic recombinati on activity, the repeat sequences from P, c. adami are rather conserve d suggesting structural or functional constraints on the protein and t andem repeats. The 93-kDa protein exists in an oligomeric form as reve aled by gel filtration chromatography and non-denaturing gel electroph oresis. A predominantly alpha-helical predicted secondary structure an d a discrepancy between the estimated molecular sizes determined from nondenaturing gel electrophoresis and gel filtration chromatography su ggest that the protein is a long rod-shaped or fibrillar, protein. Att ributes shared between the 93-kDa protein, some P. falciparum proteins with glutamate-rich tandem repeats, and cytoskeletal proteins suggest that these parasite proteins function as cytoskeletal proteins that p ossibly stabilize the erythrocyte membrane.