Modified Membranes for Protein Purification
Remarkably, sales of therapeutic proteins have reached nearly $100 billion/year. Accompanying increased protein production both in basic research and the pharmaceutical industry is a need for rapid protein separations, and affinity-based separations are often at the heart of protein purification. Despite the great success of affinity-based protein isolation, slow diffusion of large biomacromolecules to binding sites requires long purification times. As the Figure at the right suggests, affinity membranes enable rapid purification because protein solutions flow through the membrane pores. Membranes lack, however, the high surface area that is found in most beads, so their binding capacities are low. We modify membranes with polyelectrolyte multilayers and then derivatize them with affinity groups that capture specific proteins. Highly water-swollen films give rise to membranes that bind around 100 mg of protein/cm3. This capacity is 3-fold higher than that of commercial membranes and may lead to new, rapid purification techniques.
The purification procedure simply includes loading the membrane, washing, and eluting, and the whole process may occur within 5 minutes. The electrophoretic gel at the right clearly shows the high protein purity (>95%). The technology for preparing these membranes is now part of a licensed product line from Takarabio that includes spin membranes (below) and 96-well membrane plates. Future studies aim to develop a wide range of affinity membranes for capture and analysis of proteins, including antibodies. We are grateful to the US National Science Foundation (CHE-1152762 and CHE-1506315) and the U.S. National Institutes of Health (GM080511) for funding these studies, and to the many students who have participated in this work.