Dynamic and equilibrium performance of sensors based on short peptide ligands for affinity adsorption of human IgG using surface plasmon resonance

This paper characterizes the potential of novel hexameric peptide ligands for on-line IgG detection in bioprocesses. Surface Plasmon Resonance (SPR) was used to study the binding of human IgG to the hexameric peptide ligand HWRGWV, which was covalently grafted to alkanethiol self-assembled monolayers (SAM) on gold surfaces. Peptide coupling on SAMs was verified, followed by covalent grafting of peptides with a removable Fmoc or acetylated N-termini via their C-termini to produce active peptide SPR sensors that were tested for IgG binding. The dynamics and extent of peptide-IgG binding were compared with results from a conventional system using protein A attached on a gold surface via disulfide monolayers. IgG binding to protein A on disulfide monolayers yielded equilibrium dissociation constants of 1.4×10-7 M. The corresponding dissociation constant value for the acetylated version of the peptide (Ac-HWRGWV) supported on alkanethiol SAM was 5.8×10-7 M and that for HWRGWV on the alkanethiol SAM (after de-protection of Fmoc-HWRGWVA) was 1.2×10-6 M. Maximum IgG binding capacities, Qm of 6.7, 3.8, and 4.1 mg m−2 were determined for the protein A and the two forms of HWRGWV-based biosensors, respectively. Real-time data for the kinetics of adsorption were used to determine the apparent rate constants for adsorption and desorption. The results were analyzed to understand the mechanism of IgG binding to the protein and peptide ligands. It was found that the peptide-IgG binding was reaction controlled, however the protein A-IgG binding mechanism was partially mass transfer (diffusion) controlled. The adsorption rate constants, ka, for the protein A ligand increased with decreasing concentration of analyte and the peptide ligand ka values was constant at different IgG concentrations and flow rates.