Human pIgR mimetic peptidic ligand for affinity purification of IgM Part II: Ligand binding characteristics

We had previously described the design of a human polymeric immunoglobulin receptor mimetic peptidic ligand, pep14 (CITLISSEGYVSSK), that bound human IgM (hIgM) selectively and exhibited negligible affinity for other Ig proteins. In the present study, pep14 was investigated for its efficacy as an affinity ligand for IgM purification. Binding buffers at varying pH and ionic strengths were investigated. 10 mM HEPES containing 150 mM NaCl at pH 7.4 was found to be the optimum binding buffer. Equilibrium studies on pep14-immobilized-silica microspheres indicated a binding capacity of 5.9 mg hIgM/g of silica–amine microspheres and an association constant of 3.2 × 106 M−1. Exposure of pep14 to a synthetic mixture comprising hIgM, hIgG1 and bovine serum albumin had no adverse effect on the binding capacity and specificity of pep14. Experimental results highlighted the uniqueness of pep14 in capturing hIgM even at concentrations as low as 10 μg/mL. Surface plasmon resonance based studies suggested that while pep14 exhibited affinity to human and rabbit IgM, pep14 failed to interact with mouse IgM. pep14 was resistant to column-sanitizing agents including 20% ethanol and 70% ethanol, although exposure to 100 mM and 500 mM sodium hydroxide resulted in hydrolysis.

► We studied the efficacy of the designed ligand for IgM capture.
► This was done at various operating conditions, such as pH and ionic strength.
► The ligand was immobilized on silica beads to investigate the ligand binding capacity.
► Ligand specificity was tested against various feed types.
► Binding constants for the affinity attachment of IgM to the ligand were reported.