Ligand binding assays with recombinant proteins refolded on an affinity matrix.

This paper describes a procedure for performing ligand binding assays with recombinant proteins or protein fragments that can bind to an affinity matrix in the presence or absence of a denaturing agent but which require the presence of the denaturing agent to remain in solution. The method involves coupling of a known amount of the protein in a denaturing medium to a known amount of the affinity matrix, replacing the denaturing agent with a physiological buffer, and finally using the suspension of this protein-coupled matrix as the source of the recombinant protein to be studied for its functional properties. A constant volume of this suspension is incubated with different concentrations of a radiolabeled ligand. Radioactivity bound to the protein-coupled affinity matrix is determined after centrifugation and washing of the pellet. Nonspecific binding is determined either by using the uncoupled affinity matrix or by the standard technique of measuring the binding in the presence of excess unlabeled ligand.