Theileria parva 104 kDa microneme--rhoptry protein is membrane-anchored by a non-cleaved amino-terminal signal sequence for entry into the endoplasmic reticulum.
The 104 kDa microneme-rhoptry protein (p104) is the only known apical complex organelle-specific protein of Theileria parva. p104 exhibits striking structural similarities to circumsporozoite protein and sporozoite surface protein 2 of Plasmodium yoelii. Their primary sequences contain two hydrophobic segments, located at the amino-and the carboxy-terminus. The p104 amino-terminal hydrophobic region was suggested to be a signal peptide for entry into the endoplasmic reticulum and the extreme carboxy-terminal region to function as a membrane anchor. We have studied the biogenesis of p104 in a cell-free expression system and found that p104 is co-translationally transported into membranes derived from endoplasmic reticulum. The amino-terminal signal peptide is not cleaved off and anchors the protein in the membrane with the carboxy-terminal portion translocated into the lumen. We suggest that in vivo p104 is co-translationally integrated into the membrane of the endoplasmic reticulum, from where it is further transported to the microneme-rhoptry complex. Thus, p104 appears to be a suitable marker to study the development of micronemes and rhoptries in T. parva.
Ebel
T
T
Vienna International Research Cooperation Center, Department of Vascular Biology and Thrombosis Research, University of Vienna, Austria.
Gerhards
J
J
Binder
B R
BR
Lipp
J
J
D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D015388:Organelles / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000737:chemistry*; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016797:Theileria parva / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D008565:Membrane Proteins; D021382:Protein Sorting Signals; D015800:Protozoan Proteins