An immunodominant site of gamma-zein1 is in the region of tandem hexapeptide repeats.

The immunochemical data from studies with polyclonal antisera to gamma-zein1, the 27 kD component of the maize prolamin, indicated that the region containing 8 tandem repeats of the sequence PPPVHL is an immunodominant site. In one case, the entire antibody repertoire of an antiserum recognized epitope(s) within this region. Three 17-mer oligopeptides corresponding to the predicted antigenic epitopes of gamma-zein1 were synthesized and reacted with three different anti-gamma-zein1 sera in order to map antigenic sites in the intact protein. These antisera yielded positive reactions with a 17-mer peptide (peptide 37), which was not in a hydrophilic maximum but derived from the repeat region. The same antisera gave little or no reaction with other peptides (peptides 38 and 39), both of which were in a hydrophilic maximum. In addition, an antiserum to peptide 37 reacted strongly with both the homologous antigen and the intact gamma-zein1. Peptide 37 also blocked the binding of antisera to gamma-zein1 in competition assays. Subsequently, the shorter 6-mer (peptide 82) and 12-mer (peptide 80) versions of peptide 37 were synthesized, and both reacted with anti-peptide 37 serum and also with each of the three anti-gamma-zein1 sera. In these reactions and in competition assays, the reactivity and the blocking ability increased in proportion to the length of the peptide. Based on these data, it was concluded that the repeat region of gamma-zein1 is the site of one or more continuous immunodominant epitopes. The data also suggest that the repeat region is exposed on the surface of the folded protein and probably occur as a mobile, random coil.