Protein purification - (Sep/17/2008 )

Is it useful to Tag proteins for purification purposes? Some say that it might interfere with protein folding. Anyway, I would like some opinions on why it would or would not be advantageous to tag a protein

It is true that addition of a tag might interfere with protein function. To minimize the effect you can try to add the tag away from the depicted active site of the protein. Of course you should also take into consideration how thw protein folds. You may also go with smaller tags such as a 6-his, Flag tag or S-Tag, which only barely increase the size. Addition of bigger tags such as GST might also be useful in getting the protein in soluble form if your protein is hydrophobic. I personally prefer adddition of tags because I feel they are more likely to produce pure proteins after the columns. If you go with size exclusion or ion exchange other proteins around the same size or pI will come along and multiple columns will be needed for purification. Besides tags are also useful if you want to check your expression on a western blot, since there are numerous companies selling anti-tag antibodies. This is qite handly especially if you don't have an antibody against your protein of interest. Lastly tags can be removed by special proteinases if you have to get rid of them. But you should keep in mind that doing so will greatly diminish your yield. Hope that helps.