GST-GFP Purification Problem

immunechem immune at intergate.bc.ca
Sat Feb 13 20:12:15 EST 1999


GSH has chelation properties like diacetic acids. your GFP may be metal 
containing protein (I don't know). The major protein bindin force is 
hydrophobic, hydrogen-bonding n ionic exchange. The chelation is 
somewhat different from ionic or salt bridge. If it is true, you have to 
 add EDTA and EGTA to the elution buffer (free GSH). If it is 
hydrophobic binding more strong, then add detergent. If H-bonding, 
acid/base maybe needed in the elution buffer. 

If you don't need activity of the protein, try glycine buffer (pH 2.5) 
may help.




In article <7a4mmt$ona$1 at news.doit.wisc.edu>, 
klenchin at REMOVE_TO_REPLY.facstaff.wisc.edu says...
>
>In article <36C58FEE.1B965825 at blue.weeg.uiowa.edu>, 
>moyerowl at NOSPAM.blue.weeg.uiowa.edu wrote:
>>We are trying to purify a fusion protein consisting of GST with GFP
>>fused to its C-terminus.  The protein seems to be expressed fairly 
well
>>and is soluble.  The supernatant is green due to the high 
concentration
>>of GFP.  When sepharose-GSH beads are added, the supernatant loses its
>>green color and now the beads are green.  So far, so good.  Now the 
bad
>>part.  We can't seem to elute the fusion protein even with very high 
GSH
>>concentrations.  Other GST fusion proteins have been purified by us
>>using this same protocol.  Any advice/suggestions/wild guesses would 
be
>>much appreciated.
>>
>
>Gosh, whatever happened to a common sense? 
>
>If there is no affinity elution under standard conditions, then the 
>true affinity binding is too strong or there is another mode of binding
>involved. Then one wants to either weaken affinity interaction or 
disrupt
>additonal binding mode. In either case, there are essentially only two
>types of interactions involved: Ionic and hydrophobic. Naturally, 
trying 
>high salt or detergents would be the first thing to do. Simple, right?
>
>        - Dima




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