Purification of Maltose Binding Protein By Starch Precipitation

A central step in the production of high purity proteins is their recovery and purification.  The maltose binding protein (MBP) affinity tag is commonly used in this process, since it has the ability to selectively bind to immobilized amylose.  I am exploring the possibility of using a commercial grade cationic starch, which contains large amounts of amylose as part of its polymer backbone, and a salting out method to precipitate an MBP-tagged protein.  Different salts including sodium chloride, ammonium sulfate, sodium sulfate and magnesium sulfate can selectively precipitate starch, which will be bound to the MBP-tagged protein, thus co-purifying it.  Varying the salt solutions will allow the ideal composition and concentration of the salt solution for this purification method to be determined.  The effectiveness of the approach will be measured through gel electrophoresis, allowing the recovery and yield of the purified proteins to be quantified.  Because starch and salts are relatively cheap, the success of this approach will lead to a new, feasible option for mass purification and production of proteins.  At this time, the expression and starch-salt purification of the MBP-tagged protein is still in progress.  The data includes analysis of electrophoresis gels and a comparison between this starch-salt method and other, standard purification methods.