Development of a Resin-Free Protein Purification Technique Utilizing Unique Biochemical Properties of the E. coli SSB Protein

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Mark Soffe, Utah State University

Life Sciences

SSBs are DNA binding proteins that are essential components of cells and play key roles in DNA replication, repair, and recombination. Here we utilize two biochemical properties associated with the E. coli SSB protein to develop a novel procedure to purify proteins using a resin-free strategy. 1. E. coli SSB binds to single stranded DNA (ssDNA) with extremely high affinity (K = 1013 M-1), indicating very tight binding. 2. It is also a unique protein with respect to its purification – it is possible to obtain greater than 95% pure SSB from the total cell lysate without using any sort of column or resin, utilizing polyethyleneimine (PEI) and ammonium sulfate precipitation. Our design uses SSB as an affinity/solubility tag to enhance the solubility and expression of difficult-to-purify proteins, and allows for the simple, resin-free purification using PEI and ammonium sulfate precipitation. There also may be a possibility to co-express protein dimers and possibly tetramers using this method. Constructs have been made that include the SSB gene, along with the ability to fuse any gene of interest, as well as a TEV Protease cleavage sequence allowing for proteolytic cleavage after gene expression. Two genes of interest have been cloned in thus far—TEV protease and Rad51. In this proposal I outline experiments to develop this strategy further and test our proof of principle concept and its application to a broader set of target proteins.