Low-resolution epitope characterisation in a family of seed apolipoproteins using polyclonal antibodies

Polyclonal antibodies raised against a range of seed apolipoproteins from the family Cruciferae have been used for the first time for low resolution epitope characterisation. Antibodies were raised against the major seed apolipoproteins of Brassica napus, Sinapis alba and Raphanus sativum. In each case, the antibodies recognized, in addition to the 19-20 kDa apolipoprotein to which they were raised, similar 19-20 kDa apolipoproteins from a wide range of species in the family Cruciferae, but not in other plant families. Homologous or heterologous two-sites (sandwich) assays were performed with the format [antibody A - test apolipoprotein - antibody B - 2 degrees antibody]. The results showed a drastically reduced antibody B binding by apolipoproteins preincubated with an antibody A. This indicated the presence of a single major epitope on many of the apolipoproteins. The antigenicity of native and denatured apolipoproteins was similar, although the antigenicity of the former was much more readily destroyed by proteinase attack. It is concluded that there are relatively few major epitopes present on the Cruciferae apolipoproteins and it is suggested that these epitopes are localized on the small hydrophilic surface-exposed C- and N-terminal domains of the apolipoproteins.