Eimeria tenella sporozoites and merozoites differentially express glycosylphosphatidylinositol-anchored variant surface proteins.
Little is known about glycosylphosphatidylinositol (GPI)-linked surface proteins in the coccidian parasite Eimeria tenella. Examination of 28,550 EST sequences from the sporozoite and second merozoite developmental stages of the parasite led to the identification of 37 potential GPI-linked variant surface proteins, termed EtSAGs. Analysis of the complete nucleotide sequences of 23 EtSAG genes separated them into two multi-gene families. All the predicted EtSAG proteins (which vary in length from 228 to 271 residues) have an N-terminal hydrophobic signal peptide, a C-terminal hydrophobic GPI signal-anchor peptide and an extracellular domain organised around six cysteine residues, the positions of which are conserved within each family. Using specific antibodies against a small number of recombinant-expressed EtSAGs, the surface localisation and GPI-anchorage of members of both families was confirmed experimentally. Expression of EtSAGs is differentially regulated between the oocyst/sporozoite and second generation merozoite stages, with only one expressed specifically in the sporozoite, a small number expressed in both stages and the majority expressed specifically in the second generation merozoite. Preliminary data support a model in which multiple variant surface antigens are co-expressed on individual parasites, rather than a model of antigenic switching. The biological role(s) of EtSAGs and the effect(s) that expression of a complex repertoire of variant surface antigens by the second generation merozoite has on host adapted immunity are unknown.
Division of Molecular Biology, Institute for Animal Health, Compton, Newbury, Berkshire RG20 7NN, UK.
Enrique
E
Tabarés
David
D
Ferguson
Julie
J
Clark
Puay-Eng
PE
Soon
Kiew-Lian
KL
Wan
Fiona
F
Tomley
D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics / Q000378:metabolism; D000954:Antigens, Surface / Q000235:genetics* / Q000378:metabolism; D017124:Conserved Sequence; D016054:DNA, Protozoan / Q000737:chemistry / Q000302:isolation & purification; D016786:Eimeria tenella / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D005786:Gene Expression Regulation; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
D000953:Antigens, Protozoan; D000954:Antigens, Surface; D016054:DNA, Protozoan; D017261:Glycosylphosphatidylinositols; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D015800:Protozoan Proteins