Epitope mapping reveals conserved regions of an auxin-binding protein

There is now good evidence that maize (Zea mays) auxin-binding protein (ABP) functions as a receptor. We have synthesized sequential overlapping hexapeptides to map the epitopes recognized by a number of antisera to ABP. Only a few regions of the protein are recognized, and these are shown to be exposed on the surface. Three epitopes predominate, and these are clustered around, but do not include, the glycosylation site. A comparison is made between these maps of sera against purified ABP, maps of sera raised against recombinant maize ABP expressed in Escherichia coli and computer antigenicity predictions. Our anti-(maize ABP) serum recognizes ABP counterparts in other plant species. We have used immunoblotting to affinity-purify the immunoglobulins which cross-react from the antiserum. Epitope mapping of these immunoglobulins suggests that two of the three predominant epitopes may be conserved in both monocotyledonous and dicotyledonous plants. The possible functional significance of these conserved epitopes is discussed.