AFFINITY PRECIPITATION OF AN ANTIBODY BY LIGAND-MODIFIED PHOSPHOLIPIDS

A new method for the selective precipitation of proteins is applied to the isolation and purification of an antibody. Ligand-modified phosph olipids (LMPs) are solubilized by the nonionic ethoxylated alcohol det ergent, resulting in small (50 to 100 Angstrom) micellar aggregates of LMPs and surfactant. When introduced into protein solutions containin g an antibody for which the LMP has specific affinity, the ligand bind s to the protein. Hydrophobic interactions between phospholipid tail g roups bound to the protein molecules result in an insoluble precipitat e. Polyclonal and monoclonal antibiotin antibody (pABA and mABA) are s hown to be selectively precipitated using ratios of dimyristoylphospha tidylethanolamidobiotin (DMPE-B) to ABA ranging from 1:1 to 19:1. The kinetics and yield of the precipitation achieve a maximum at a ratio o f DMPE-B to ABA of approximately 7:1. The kinetics and magnitude of th e turbidity change are modeled using the Mie theory of light scatterin g coupled with the Smoluchowski theory of aggregation. The kinetics ar e shown to be enhanced significantly by the addition of salt. In parti cular, the addition of 0.5 M ammonium sulfate salt increases the rate of precipitation by more than an order of magnitude. It is demonstrate d that pABA can be recovered with total activity yields of 60% to 70% from mixtures containing nonspecific IgG antibodies in very high purit y (> 99%). (C) 1994 John Wiley and Sons, Inc.