DETERMINATION AND ANALYSIS OF ANTIGENIC EPITOPES OF PROSTATE-SPECIFICANTIGEN (PSA) AND HUMAN GLANDULAR KALLIKREIN-2 (HK2) USING SYNTHETIC PEPTIDES AND COMPUTER MODELING

Prostate specific antigen (PSA) and human glandular kallikrein 2 (hK2) , produced essentially by the prostate gland, are 237-amino acid monom eric proteins, with 79% identity in primary structure. Twenty-five ant i-PSA monoclonal antibodies (Mabs) were studied for binding to a large array of synthetic linear peptides selected from computer models of P SA and hK2, as well as to biotinylated peptides covering thr entire PS A sequence. Sixteen of the Mabs were bound to linear peptides forming four independent binding regions (I-IV). Binding region I was localize d to amino acid residues 1-13 (identical sequence for PSA and hK2), II (a and b) was localized to residues 53-64, III (a and b) was localize d to residues 80-91 (= kallikrein loop), and IV was localized to resid ues 151-164. Mabs binding to regions I and IIa were reactive with free PSA, PSA-ACT complex, and with hK2; Mabs binding to regions IIb, IIIa , and IV were reactive with free PSA and PSA-ACT complex, but unreacti ve with hK2; Mabs binding to region mb detected free PSA only. All Mab s tested (n = 7) specific for free PSA reacted with kallikrein loop (b inding region mb). The presence of Mabs interacting with binding regio n I did not inhibit the catalytic activity of PSA, whereas Mabs intera cting with other binding regions inhibited the catalysis. Theoretical model structures of PSA, hK2, and the PSA-ACT complex were combined wi th the presented data to suggest an overall orientation of PSA with re gard to ACT.