| Abstract;The relation between structure of haptens and the esterolytic activities of antibodies was investigated in order to get a proteolytic antibody. We synthesized two types of hapten of phenylalanine analog, the negatively charged phosphonate derivative (hapten 1) and the neutral phosphonamidate derivative (hapten 2). Seventeen out of 41 monoclonal antibodies taken from the hapten 1 hydrolyzed the relevant phenylalanine ester R-3, the rate enhancements being kcat/kun=163-4400. In contrast, none of 27 monoclonal antibodies generated against the hapten 2 had catalytic activity. We examined structural and electronic properties of modeled haptens, i.e. methyl hydrogen 1-acetylamino-2-phenylethyl phosphonate (4) and N-[(1-acetylamino-2-phenylethyl)methoxyphosphinyl]-methylamine (5), corresponding to the hapten 1 and 2 respectively, by ab initio. We found that the negative electrostatic potential surface of phosphonyl oxygen of 4 (-120--168kcal/mol) was much larger than that of 5 (-20--70kcal/mol). Further, the esterolytic antibodies were found to bind strongly to hapten 1 and the modeled hapten 4, as compared with the antibodies without activity. These results indicate that the size of electrostatic potential surface is an important cue for a hapten eliciting esterolytic activity. (author abst.) |
