Cloning and sequencing the genes of glutamate-rich proteins from Plasmodium chabaudi
Description
During the malaria infection of the red blood cell, the parasite causes several modifications to the host cell membrane. These modifications include decrease in deformability and elasticity of the membrane, increase in the permeability to metabolites and association of parasite derived proteins to the membrane. Some of the proteins include the knob associated protein, the mature erythrocyte surface antigen and the acidic phosphoproteins. Acidic phosphoproteins have been described in P. berghei, P. chabaudi and P. falciparum. A 93 kDa P. chabaudi acidic phosphoprotein (Pc(em)93) has been well characterized. This protein is expressed early after merozoite invasion and rapidly transported to the membrane. Differential solubility and inside-out vesicle binding studies indicate that it interacts with the red blood cell membrane cytoskeleton. In the present study the gene of a 93 kDa P. chabaudi protein was cloned and sequenced. The early expression and rapid transport of Pc(em)93 to the membrane suggests that it may play an important role in the life cycle of the parasite. The sequence of the gene is consistent with the 93 kDa protein being a filamentous cytoskeletal-like protein. Therefore, Pc(em)93 might function as a cytoskeletal protein to stabilize the erythrocyte membrane after the merozoite invasion. In addition, a previously unknown P. chabaudi gene was cloned. This gene expresses a protein with cross-reactive epitopes also present in Pc(em)93. Both genes have glutamate-rich tandem repeats that contain glutamate dipeptides like many other Plasmodium proteins. Cross-reacting epitopes have been map to the glutamate dipeptide in the tandem repeats of some glutamate-rich Plasmodium proteins. Comparison of the tandem repeats of Pc(em)93 with other P. chabaudi strains shows an exact seven repeat duplication in one of the strains. This information supports the hypothesis that unequal crossing-over plays a role in the generation of tandem repeats and general diversity between strains or species