For stimuli responsive polymers (smart polymers) see outline.

Affinity Precipitation In General

In comparison to nonspecific precipitation using as for example ammonium sulphate precipitation, affinity precipitation makes use of the selective binding an an affinity molecule to a target molcule. 

A distinction is sometimes drawn between first and second order affinity precipitation.

(I)  In first order affinity precipitation, both the affinity molecule and the target molecule have two binding sites, so that it is possible for a network to form between the two molecules and an affinity complex is formed that sediments at a specific size.

Ambrosius (US 14/151949, published as US 2014/0128578) disclose affinity precipitation using a binding protein with two binding sites such as a dimer of protein A or protein G. Preferably, the monomers of the dimer are linked to one another via a disulphide bond.

(II) In second order affinity affinity precipitation, the affinity molecule is bound to a stimulable substance, usually a polymer, which can change in response to various conditions like pH or temeprature, usually a polymer. The stimulatable substance changes its solubility characteristics as a result of a change in the ambient conditions, such as e.g. a shift in the pH or temperature, and precipitation occurs. Unlike first order affinity precipitation, there is no need for a bifunctional affinity molecule or for a bifunctional target molecule. 

For example, Stayton (US 7,625,764) discloses precipitation of IgG (Fc-protein) using Protein A-conjugates. The conjugation partner for the Protein A is stimulus responsive polymer which includes pH and temperature sensitive polymers.

Specific Affinity Precipitation Molecules

Protein A/G:

SpA forms large networks with IgG to form a precipitate and both the dimeric and tretrameric domain B proteins form precipitates with IgG as well. (Saito (Protein Engineering 2(6), 481-487, 1989)

Ambrosius (US 14/151949, published as US 2014/0128578) discloses a process for the selective concentration of immunoglobuilins or other proteins that contain an Fc domain by using an Fc-binding protein such as Protein A or G with precisely two binding sites under conditions that allow binding to occur, separating the precipitate fromt he liquid phase and undoing/eluting the binding of the target protein from the Fc binding protein. In one embodiment the Fc binding protein is a dimer of an Fc binidng domain of Protein A or G. 

Ligand (e.g., Protein A) attached to coodinating moiety (e.g., M+):

Patchornik (US 2006/0121519) discloses ligands such as protein A, which are attached to at least one coordinating moiety such as a bis-chelator capable of directing the composition of matter to form a non-coavlent complex when co-incubated with a coordinator ion or molecule such as M+, M2+, M3+. The target protein of interest can then be recoved form the precipitate formed. In one embodiment preicpitation of a target molecule is obtained using biotin as the coordinating moeity. A ligand with a covelaently bound bi-biotin or biotin derviative sucha sDSB-X Biotein is incubated in the presence of the target molecule. Introducstion of avidin (or its derivatives) creates a netword comprising ligand-coorindating moiety (biotin) target molecuel avidin. In anotehr embodiment purification of an antibody is demonstrated using a modified Protein A (ProA-CAT) adn Fe3+ions. Binding of the ProA-CAT to teh target IgG leads to the formation of the ProA-CAT target IgG) soluble complex. Additon of Fe3+ ions to the complex geenrates insoluble macro-complexes containing the target IgG. Impurities eleft in the supernatant are discarded via centrifugation. Target IgG is eluted under acidic conditions without dissociating the ProA-CatFe3″ macro-complex of the insoluble pellet.