Review of conformation-specific affinity purification methods for plasma vitamin K-dependent proteins.

There are seven known vitamin K-dependent proteins in blood. These proteins require calcium ion for expressing their full biological activities. Calcium ion also induces conformational changes in this class of proteins. Taking advantage of the ligand induced conformational changes, a number of unique approaches of affinity chromatography have been developed. These methodologies have been very useful tools for both the purification and for understanding the structure-function relationships of this class of proteins. One method is the use of metal ion dependent immunoaffinity chromatography. The antigen can be dissociated from the antibodies with either the removal or addition of calcium ion under physiological conditions. The other method is pseudoaffinity chromatography. This method uses conventional ion-exchange or hydrophobic resin and manipulates the mobilities of the proteins on these resins by the presence or absence of calcium ions. Researchers working with other calcium binding proteins or other proteins that are known to undergo ligand induced conformational changes may benefit from the experience of these unique conformation-specific affinity chromatography approaches.