Conformational Changes in a Synthetic Antigen Induced by Specific Antibodies

Abstract

The high molecular weight copolymer (mol.wt. = 75000) containing the repeating sequence-(L-Tyr-L-Ala-L-G1u)-and denoted as polypeptide (Tyr-Ala-Gh), has previously been shown to possess an a-helical structure under physiological conditions. Studies were performed t o check whether monovalent fragments of antibodies derived from anti-(Tyr-Ala-Glu), antibodies could convert the partially helical oligopeptide (Tyr-Ala-Glu),, into a more helical conformation.Circular dichroic spectra of mixtures of the monovalent antibody fragments with (Tyr-AlaGlu),, were measured a t two different concentrations of both components. Analogous experiments were done with the same fragments and the polypeptide (Tyr-Ah-Glu),. When anti-(Tyr-AlaGlu), antibody fragments were mixed with (Tyr-Ala-Glu)13, there was a large difference spectrum centered at 278 nm, which is the ellipticity band of (Tyr-Ala-Glu),,. When the same fragments were mixed with the polypeptide (Tyr-Ah-Glu),, a difference spectrum was observed at the ellipticity band of the polypeptide centered at 275 nm. It was concluded that anti-(Tyr-Ala-Glu), monovalent antibody fragments could not only convert the (Tyr-Ala-Glu),, into a structure more similar to the polypeptide (Tyr-Ah-Glu),, but could also stabilize the helical content of this polypeptide.Interaction between two macromolecules may induce conformational changes in both of them. Thus, substrates may bring about an "induced fit" with enzyme molecules [I]. The immunochemical reaction between an antigen and an antibody may similarly result in changes both within the areas including antibody combining sites and the areas including antigenic determinants. In the case of the antibody, recent studies have suggested that a monovalent hapten causes no conformational change in the antibody molecule as detected by circular dichroic measurements [2] and by differential sedimentation [3], whereas interaction with a divalent hapten causes a slight change in frictional ratio of the antibody molecule [3].Several reports have appeared in recent years describing changes in the conformation of the antigenic molecule upon reaction with antibodies. Thus, myoglobin is converted into apomyoglobin upon reaction with anti-apomyoglobin antibodies [4], whereas enzymically inactive /3-galactosidase mutants gain activity upon reaction with antibodies to the wild type enzyme [ 5 ] .I n connection with an investigation of the role of macromolecular conformation in immunogenicity and antigenic specificity [6,7], we have described in the preceding paper [8] antibodies against conformation-dependent determinants of an &-helical copolymer of the ordered periodic sequence (Tyr-AlaGlu),. The ability of these antibodies to react with oligopeptides containing the repeating sequence L-tyrosyl-L-alanyl-L-glutamyl [8,9] as followed by their capacity to inhibit the homologous precipitin system, increased with increasing length of the oligopeptides. Thus, the tripeptide Tyr-Ala-Glu did not inhibit the precipitin reaction, (Tyr-AlaGlu), inhibited poorly, whe...

From Proteins and Protein Models to Their Use in Immunology and Immunotherapy

“…In two interesting studies, we could show how the combining site of the antibody can transconform the structure of the antigen. I mentioned earlier how antibodies to the ␣-helical polymer could help transconform a small polymer that was not yet helical into a helical shape (32). We could also demonstrate that the Fab of an antibody to p-azobenzenearsonate hapten may "suck out" the p-azobenzenearsonate moiety from its unavailable conformation within an ordered copolymer and convert it into another conformation, recognized by Fab (50).…”

“…We distinguished between conformational (conformation-dependent) and sequential determinants (31) and showed how the same peptide (Tyr-Ala-Glu) may lead to antibodies recognizing the sequence (when attached to multichain poly-DL-alanine) or recognizing an epitope defined by conformation (when the tripeptide was polymerized to give an ␣-helical structure). In addition, we could demonstrate for the first time, by circular dichroism, how antibodies to the ␣-helical polymer could help transconform into a helical shape a small polymer that was not yet helical (32). These studies led us directly to study proteins and to synthesize a macromolecule in which a synthetic "loop" peptide derived from hen egg white lysozyme was attached to branched polyalanine (33).…”

An Immunologic Approach to the Conformational Equilibria of Polypeptides

“…Schechter et al have shown that antibodies to the helical polypeptide (Tyr-Ala-Glu) are capable of "inducing" increased helicity in the oligopeptide (Tyr-Ala-Glu)i3 (22). Eq.…”

Synthetic Antigens with Sequential and Conformation‐Dependent Determinants Containing the Same l‐Tyrosyl‐l‐alanyl‐l‐glutamyl Sequence

“…Significant reaction occurs with large peptides of the (Tyr-Ala-Glu), series (n = 4, 7, 9, 13), although circular dichroic studies indicate initial formation of helical structure only with the (Tyr-Ala-Glu),, [41]. The binding of these oligopeptides may be due to their transconformation into an a-helical form as a result of contact with the combining sites of the antibodies [42].…”