Question

Using affinity chromatography, you have attempted to purify an enzyme as a fusion protein that was expressed in E. coli. SDS-PAGE analysis shows that the eluted sample contains the enzyme and it appears to be very pure.

Briefly describe, in general terms, a method you could use to determine the concentration of the enzyme in the eluted sample. Describe the advantages and disadvantages of your approach.

Answer 1

Affinity chromatography is an approach protein biologist use for purification of recombinant proteins which are tagged with certain enzyme (for example GST) in the E. coli cells. Since they are GST tagged so during elution through column they may easily be displaced in a buffer that is free of any glutathione.

Such protein would be pure one and can be categorized over SDS gel for qualitative analysis of proteins and size of protein can be determined for further validation. We can judge the protein content (concentration) of eluted/purified enzymes through spectrophotometer, since we can expect low protein content so Bradford or BCA methods would be appropriate for the same.

Advantage of such protein is that, we can get ultra-purified protein fraction (fused protein with GST) by this method and will not have any contaminant if procedure and all conditioned are followed appropriately but the yield of the protein would be very low as you may lose significant amount of protein during affinity chromatography and for large quantity, you have to run samples for several time.