Conformational Changes in a Synthetic Antigen Induced by Specific Antibodies

The high molecular weight copolymer (mol. wt. = 75 000) containing the repeating sequence–( l ‐Tyr‐ l ‐Ala‐ l ‐Glu)–and denoted as polypeptide (Tyr‐Ala‐Glu) n has previously been shown to possess an α‐helical structure under physiological conditions. Studies were performed to check whether monovalent fragments of antibodies derived from anti‐(Tyr‐Ala‐Glu) n antibodies could convert the partially helical oligopeptide (Tyr‐Ala‐Glu) 13 into a more helical conformation. Circular dichroic spectra of mixtures of the monovalent antibody fragments with (Tyr‐Ala‐Glu) 13 were measured at two different concentrations of both components. Analogous experiments were done with the same fragments and the polypeptide (Tyr‐Ala‐Glu) n . When anti‐(Tyr‐Ala‐Glu) n antibody fragments were mixed with (Tyr‐Ala‐Glu) 13 . When the same fragments were mixed with the polypeptide (Tyr‐Ala‐Glu) n , a difference spectrum was observed at the ellipticity band of the polypeptide centered at 275 nm. It was concluded that anti‐(Tyr‐Ala‐Glu) n monovalent antibody fragments could not only convert the (Tyr‐Ala‐Glu) 13 into a structure more similar to the polypeptide (Tyr‐Ala‐Glu) n , but could also stabilize the helical content of this polypeptide.