Identification of peptides that mimic the pertussis toxin binding site on bovine fetuin

Investigating pertussis toxin and its impact on vaccination

Whooping cough, caused by Bordetella pertussis, remains a major global health problem. Each year around 40 million of pertussis cases resulting in 200,000-400,000 annual deaths occur worldwide. Pertussis toxin is a major virulence factor of B. pertussis. Murine studies have shown its importance in bacterial colonization and in immunomodulation to evade innate or adaptive immunity. The toxin is composed of an A protomer expressing ADP-ribosyltransferase activity and a B oligomer, responsible for toxin binding to target cells. The toxin is also a major protective antigen in all currently available vaccines. However, vaccine escape mutants with altered toxin expression have recently been isolated in countries with high vaccination coverage illustrating the need for improved pertussis vaccines.

The ins and outs of pertussis toxin

Pertussis toxin, produced and secreted by the whooping cough agent Bordetella pertussis, is one of the most complex soluble bacterial proteins. It is actively secreted through the B. pertussis cell envelope by the Ptl secretion system, a member of the widespread type IV secretion systems. The toxin is composed of five subunits (named S1 to S5 according to their decreasing molecular weights) arranged in an A-B structure. The A protomer is composed of the enzymatically active S1 subunit, which catalyzes ADP-ribosylation of the α subunit of trimeric G proteins, thereby disturbing the metabolic functions of the target cells, leading to a variety of biological activities. The B oligomer is composed of 1S2:1S3:2S4:1S5 and is responsible for binding of the toxin to the target cell receptors and for intracellular trafficking via receptor-mediated endocytosis and retrograde transport. The toxin is one of the most important virulence factors of B. pertussis and is a component of all current vaccines against whooping cough.

Identification and refinement of a peptide affinity ligand with unique specificity for a monoclonal anti-tenascin-C antibody by screening of a phage display library

Using phage display technology, a 22-mer peptide was selected as a ligand with unique specificity for the murine monoclonal ST2146 antibody that recognizes the EGF repeats region of the human tumor-associated antigen tenascin-C. This peptide, synthesized in an 8-branched form to enhance its binding properties, is useful in replacing the native antigen in the affinity and immunoreactivity characterization of the ST2146 antibody and its biotinylated derivatives. Affinity resins, prepared by immobilizing the mimotope or its shorter 10-mer binding unit on a chromatographic support, were able to capture ST2146 directly from the hybridoma supernatant, with antibody recovery and host cell protein (HCP) reduction similar to or better than protein A sorbent, a purity degree exceeding 95%, and full recovery of antibody activity. The affinity constants of both peptides, as determined by frontal analysis of broad-zone elution affinity chromatography and BiaCore measurements, were very similar and included in a range suitable for affinity ligands. Column capacity, determined by applying a large excess of purified ST2146 to 1 mL of column bed volume, was close to 50 mg/mL for both resins. These matrices retain their ST2146 binding properties after various treatments, including sanitization, thus indicating very high stability in terms of ligand leakage and degradation. Moreover, the short form shows higher enzymatic stability, thus proving more suitable as ligand for ST2146 affinity purification.