Identification of the binding site of two monoclonal antibodies to human protamine.

We have previously developed a number of monoclonal antibodies (Mabs) that bind to protamine. One of these antibodies, Hup1N, binds to human protamine 1 but not to protamine 2. In contrast, Mab HupA binds both protamine 1 and protamine 2. The epitopes for these two Mabs were observed to overlap, and were localized to the evolutionarily conservative amino-terminal region of protamine 1. This assignment is based on antibody binding to protamine from different species in which the protamine sequence is known, as well as analysis of antibody binding to synthetic peptides and synthetic peptides with specific amino acid substitutions.