ABSTRACT
The 18-kDa protein from Mycobacterium leprae is a major target for the immune response in leprosy. We have developed a system to express this antigen in yeast as a fusion protein with the C-terminal region of the yeast membrane protein GAS1, which would render the recombinant protein anchored to the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. Cells lacking the GAS1 gene and transformed with the hybrid 18-kDa-GAS1 construct express a polypeptide that reacts with an 18-kDa-specific monoclonal antibody. In addition, these cells react with an alpha-CRD antibody after GPI-PLC treatment. The non-transformed cells are negative. These data indicate that our system may be suitable for the expression of foreign proteins in yeast in a GPI-anchored form
Subject(s)
Glycosylphosphatidylinositols/genetics , Mycobacterium leprae/immunology , Bacterial Proteins/genetics , Genes, Fungal , Genetic Vectors , Glycosylphosphatidylinositols/immunology , Membrane Glycoproteins/genetics , Membrane Glycoproteins/immunology , Mycobacterium leprae/genetics , Bacterial Proteins/immunology , Fungal Proteins/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/immunologyABSTRACT
The glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC) from trypanosoma brucei exhibits exquisite specificity for the GPI-anchor of the variant specific glycoprotein (VSG). However the evidence that it is involved in VSG metabolism in the living trypanosome is circunstantial; it shows the same life cycle stage regulated expression as the VSG, no feasible alternative substrate has been identified, and it metabolises the VSG efficiently in vitro and in vivo on hypotomic lysis. Against these considerations are the observations that the GPI-PLC is found on the cytoplasmic face of vesicles so it could not gain access to the VSG through normal vesicle fusion and that the accelerated loss of VSG from bloodstream forms on differentiation to procyclic forms occurs through the action of a protease. To try to determine the role of the GPI-PLC, a homozygous mull mutant T. brucei has been constructed. The null mutant was created by replacement of the entire gene at both alleles with selectable antibiotic resistance markers in procyclic form trypanosomes. The GPI-PLC gene is not usually expressed in procyclic forms and so, as would be expected, the null procyclics display no obvious phenotype. The null procyclics have been used to infect tsetse flies and it remains to be seen whether it is possible for them to differentiate to bloodstream forms and, if so, what the antigenic variation phenotype of the null bloodstream forms would be