Synthetic immunogens.

Abstract

Chimeras of the double chain bis-cystinyl hinge fragment 225 -232/225'-232' of human IgGl and of peptides related to human little-gastrin were synthesized, whereby the fully bioactive gastrin sequences 2-17 and 5-17 were amide-bond-linked N-and N-or C-terminally, respectively, to the hinge peptide. All the dimeric constructs proved to be efficient immunogens; however, both the configuration of the constructs and the length of the haptenic gastrin molecule were found to drastically affect the specificity of the antibody response and, thus, the type of dominant immune epitope expressed. The different degree of accessibility of the gastrin chains in the dimers is similarly reflected by their binding affinities to gastrin receptors and their bioactivities in vivo. Molecular dynamics simulations of the chimeric compounds clearly revealed that the conformational space of the gastrin peptide chains 2-17 and 5-17 is strongly restricted upon linkage to the hinge peptide. Only in the gastrin-(2-17) construct does sufficient free conformational space seem to be retained, at least for one of the two gastrin chains, in order to allow folding into the bioactive structure. This also agrees with the observation that the dimeric gastrin-(2-17) behaves like a gastrin monomer in terms of receptor binding affinity and biopotency in vivo; but it could additionally explain why an antibody response of gastrin receptor-like specificity could only be induced with this construct. The experimental data may therefore suggest a high degree of parallelism between the mechanism of recognition of the gastrin peptides in the dimeric constructs as hormonal ligands by the gastrin receptors and as haptens by the immune competent cells.

Cyclodextrin as Carrier of Peptide Hormones. Conformational and Biological Properties of β-Cyclodextrin/Gastrin Constructs

“…This result suggests that structural requirements for agonist binding are not exactly identical to those for agonist activity and that the relatively high binding affinity of 3 may result from strong unspecific binding contributions. In a previous study on the dimeric presentation of the gastrin peptide HG-[5−17] on a peptide scaffold conformational studies combined with immunological responses clearly confirmed a collapse of the two peptide chains as responsible for the strongly reduced accessibility of the construct to recognition by the CCK−B/gastrin receptor …”

Staphylococcus aureus fibronectin‐binding proteins (FnBPs)

“…This study showed Fab fragments of polyclonal antibodies to be less satisfactory in inhibition of fibronectin binding to the native receptor on the cell than had been hoped. It is possible that in the case of polyclonal antisera, peptides capable of conformational polymorphology have interacted with a diverse population of antibody-producing cells, some of which may fortuitously recognize the native epitope (23,24). It was recently reported that the multiple interaction of fibronectin with the staphylococcal receptor appears to be the mechanism acting in the attachment of staphylococci to the substrate, and that clustering of receptors cannot be ruled out (1).…”

Synthesis of single‐ and multiple‐stranded cystine‐rich peptides

“…The preceding synthetic and conformational studies on the hinge fragment HThrCysProProCysAlaProGlyOH (sequence 225–232) of IgG1 surprisingly revealed that the excised short fragment retains the ability to dimerize on air oxidation to a parallel dimer composed of the two peptide backbones in the poly‐Pro‐II helix conformation as in the intact IgG1 molecule (Figure 8). 30, 101 This ability is retained even after extending this central scaffold N‐ and/or C‐terminally with IgG1‐related and ‐unrelated peptide sequences 30, 102–104…”