Abstract
The diffusion interaction parameter (k(D) ) has been demonstrated to be a high-throughput technique for characterizing interactions between proteins in solution. k(D) reflects both attractive and repulsive interactions, including long-ranged electrostatic repulsions. Here, we plot the mutual diffusion coefficient (D(m) ) as a function of the experimentally determined Debye-Hückel-Henry surface charge (Z(DHH) ) for seven human monoclonal antibodies (mAbs) in 15 mM histidine at pH 6. We find that graphs of D(m) versus Z(DHH) intersect at Z(DHH), ~ 2.6, independent of protein concentration. The same data plotted as k(D) versus Z(DHH) show a transition from net attractive to net repulsive interactions in the same region of the Z(DHH) intersection point. These data suggest that there is a minimum surface charge necessary on these mAbs needed to overcome attractive interactions.