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 interact with the host membrane. This report describes the complete sequence and some biochemical properties of a 93-kDa Plasmodium chabaudi chabaudi protein that interacts with the host erythrocyte membrane. Approximately 40% of the deduced protein sequence consists of tandem repeats of 14 amino acids that are rich in glutamic acid residues. Comparison 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. However, in spite of this potentially high level of intragenic recombination activity, the repeat sequences from P. c. adami are rather conserved suggesting structural or functional constraints on the protein and tandem repeats. The 93-kDa protein exists in an oligomeric form as revealed by gel filtration chromatography and non-denaturing gel electrophoresis. A predominantly α-helical predicted secondary structure and a discrepancy between the estimated molecular sizes determined from non-denaturing gel electrophoresis and gel filtration chromatography suggest that the protein is a long rod-shaped or fibrillar, protein. Attributes 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 possibly stabilize the erythrocyte membrane.