Processing of Fusion Proteins with Immobilized Factor Xa

Factor Xa, with a cellulose-binding domain (CBD) fused to the C-terminus of the heavy chain (FXa-CBD), is active in solution and when immobilized on cellulose. A second derivative of factor Xa in which a hexahistidine tail is fused to the C-terminus of the heavy chain (FXa-H 6 ) also retains activity when immobilized, in this case on Ni 2+ -NTA agarose. The stabilities and activities of FXa-CBD and FXa-H 6 immobilized on cellulose and Ni 2+ -NTA agarose, respectively, are similar. Immobilized factor Xa derivatives can be used to remove affinity tags from appropriate fusion proteins without contaminating the desired product with factor Xa.