Expression in Escherichia coli and immunological characterization of three zona pellucida proteins (ZP1, ZP2, and ZP3) from a marsupial, the brushtail possum (Trichosurus vulpecula).

The brushtail possum (Trichosurus vulpecula) zona pellucida (ZP) is composed of three major glycoproteins, designated ZP1, ZP2, and ZP3 based on their size and homology with eutherian ZP proteins. These proteins are candidate antigens for the development of an immunocontraceptive vaccine to control the fertility of the brushtail possum in New Zealand, where it is an introduced pest. In order to further their immunological and functional characterization, recombinant possum ZP proteins were produced in Escherichia coli (E. coli) strain JM109, M15, SG13009, or BL21 codon plus. Each of the proteins produced possessed a N-terminal six histidine tag (His)(6) to facilitate purification and consisted of amino acid (aa) residues 18-471 of possum ZP1, aa residues 40-311 of ZP2 (ZP2-N), aa residues 305-634 of ZP2 (ZP2-C), and aa residues 23-342 of ZP3. Immunoblot using anti-RGS(His)(4) antibodies and polyclonal rabbit anti-porcine ZP antibodies detected major bands at 54 kDa for ZP1, 32 kDa for ZP2-N, 39 kDa for ZP2-C, and 40 kDa for ZP3. Immunization of male and female rabbits with ZP2-N, ZP2-C, and ZP3 purified on Ni-NTA resin under denaturing conditions generated antibodies reactive with recombinant ZP proteins on Western blot and with native ZP proteins in possum ovarian sections using immunofluorescence. Antibodies generated against ZP1 in the same way were reactive with recombinant ZP proteins on Western blot only. The recombinant possum ZP proteins and specific antibodies produced in this study give an indication of the antigenic relationship of the possum ZP proteins and are vital tools for future studies of sperm-ZP binding in marsupials and for the evaluation of ZP-based contraceptive vaccines in possums and other marsupials.