Dissociation of the protein G - IgG complex by fluidic force discrimination

  • A. el Fattahi

Student thesis: Master


A laminar flow chamber has been fabricated and used to investigate the bond strength between protein G and a mouse immunoglobulin G (IgG) adsorbed on a polystyrene substrate. The bond strength was investigated by applying a hydrodynamic force on protein G-coated beads using a laminar flow. The force acting on the beads was quantified by determining the shear rate acting on the bead derived from the volumetric flow rate in the chamber. This flow rate was verified by measuring the speed of unbound beads flowing through the flow chamber. The dissociation behaviour of protein G-coated beads attached to substrates incubated with IgG concentrations of 50 nM, 100 nM and 1?M was studied at an applied constant force of 75 pN. It has been shown that approximately 65% of the beads bound to a substrate functionalized with 50 nM of IgG is attached to the surface with a single specific protein G- IgG bond. Additionally, dissociation of beads attached to a substrate incubated with IgG concentration of 50 nM under constant forces of 30, 50, 75, 100 and 150 pN, shows that the dissociation rate increases with increasing the applied force. Above 75 pN, the dissociation can be described by three different rates: a fast dissociation rate that can be attributed to nonspecific bonds, followed by a slower decay attributed to beads bound through a single protein G-IgG complex and a very slow decay that corresponds to beads bound through multiple protein G-IgG complexes. At low forces, 30 and 50 pN, beads dissociation behaviour can be satisfactory described by only two dissociation rates. One dissociation rate can be attributed to the fraction of non-specific bonds and the other effective dissociation rate is assigned to the sum of single bound beads and multiple bound beads. Finally, the spontaneous dissociation rate at zero force (koff ) and the position of the energy barrier for dissociation x of the protein G-mouse IgG complex are (3.4± 0.5) 10-4 s-1and (0.069 ±0.002) nm respectively. These values are in close agreement with results from the literature.
Date of Award30 Apr 2010
Original languageEnglish
SupervisorLeo J. van IJzendoorn (Supervisor 1)

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