In vitro biosynthesis and in vivo processing of the major microneme antigen of Sarcocystis muris cyst merozoites.
The cDNA clone pSM/1.6 encoding the 26.5-kDa precursor molecule of the 16/17-kDa microneme antigen of Sarcocystis muris cyst merozoites was expressed in a cell-free translation/translocation system to study translocation of the protein across membranes. The antigen was found to be translocated across heterologous endoplasmic reticulum membranes. Translocation was accompanied by cleavage of a signal peptide to create a 23-kDa polypeptide that was completely protected from digestion with proteinase K. Pulse-chase analysis of [35S]-methionine-labeled S. muris cyst merozoites demonstrated that the 16/17-kDa antigen derived from a 23-kDa precursor molecule and that its processing occurred at between a few minutes and 2 h after biosynthesis. This leads to the conclusion that the native microneme antigen is secreted from the parasite cell via the endoplasmic reticulum. Sorting into micronemes might occur during transition through a Golgi-like structure, involving cleavage of the hydrophilic propeptide to create the mature 16/17-kDa protein.
Klein
H
H
Fakultät für Biologie, Arbeitsgruppe Molekulare Genetik, Ruhr-Universität Bochum, Germany.
Mehlhorn
H
H
Rüger
W
W
D000818:Animals; D017951:Antigen Presentation; D000953:Antigens, Protozoan / Q000032:analysis* / Q000096:biosynthesis / Q000235:genetics; D016054:DNA, Protozoan; D004285:Dogs; D015870:Gene Expression; D051379:Mice; D008807:Mice, Inbred BALB C; D010179:Pancreas / Q000378:metabolism; D012522:Sarcocystis / Q000276:immunology*
D000953:Antigens, Protozoan; D016054:DNA, Protozoan