Protein purification is a vital and expensive step in biomedical research and in the development and manufacturing of therapeutic proteins. Unfortunately, affinity methods, which are at the heart of most protein purifications, often present a bottleneck in the separation process because of slow diffusion of proteins in the pores of chromatographic gels. Protein-absorbing membranes can overcome this challenge because convective flow through membrane pores provides rapid mass transport to binding sites. Such flow can also effectively remove undesired proteins to increase purity. However, membrane absorbers are not widely used for protein isolation because they have low protein-binding capacities.
The aim of this work is to modify membranes with functional polymer brushes to increase protein-binding capacities by an order of magnitude and enable rapid, selective protein purification. Additionally, properly designed brushes will be resistant to nonspecific adsorption and provide new methods for purification of """"""""sticky"""""""" proteins that are not amenable to column-based purification. This research will involve synthesis and characterization of polymer brush-modified membranes that bind histidine6- and glutathione S-transferrase-tagged proteins with minimal nonspecific adsorption. Preliminary results demonstrated purification of a histidine6-tagged protein in a cell extract, with a purity that greatly exceeds similar resin-based purification. Future work aims at developing brush-modified membranes in polymeric supports with pore sizes that will allow large increases in permeability. This will permit the use of lower pressures and thicker membranes with much higher capacities. Formation of such membranes will require both development of new synthetic methods that are compatible with polymer supports and growth of thicker brushes that rapidly bind more protein. Hence, protein binding and non-specific adsorption will be examined as a function of brush thickness, composition, density, and functionalization, and membrane composition and geometry. With new membranes in hand, a variety of tagged proteins expressed in E. coli will be purified including SNAP-50, human MIP synthase, and SNAPc complex. MIP synthase is vital for inositol biosynthesis, while SNAP proteins are critical in gene expression. Additionally, SNAP-50 provides an example of a sticky protein that cannot be purified with typical affinity gels.
This research will yield rapid, inexpensive methods for isolating remarkably pure proteins. Such techniques will be crucial in production of therapeutic proteins as well as research studies aimed at isolating proteins to understand their structure and health- related function.
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