Troubleshooting Guide for Purification using NEBExpress^® Ni Resin

Low protein yield

or

No protein eluted

Low expression of target protein

• Check the expression level of the protein in the crude extract by running an SDS-PAGE protein gel.
• Load a larger quantity of crude extract onto the column.
• Concentrate the crude extract prior to loading on the column.

Target protein did not bind to the nickel resin

• If you’ve prepared your own lysis/binding buffer, ensure the pH is above 6.5 and the buffer does not contain imidazole.
• Perform a western blot to determine if a His-tag is present. If the blot is positive, it is possible that the tag is sterically blocked from binding to the resin; attempt purification under denaturing conditions, change location of His-tag (N vs C terminus) or add linker between His-tag and target protein in fusion construct.

Target protein is still bound to the resin

• Confirm that target protein is bound to the resin by taking an aliquot of the resin, stripping with SDS gel loading buffer and analyzing via SDS-PAGE.
• Ensure the Elution Buffer was correctly prepared to contain 500 mM Imidazole.
• Allow column resin to interact with elution buffer at 4°C for an extended period of time (30 minutes to 24 hours)

Target protein is degraded, or the his-tag is missing

• Include protease inhibitors in the Lysis/Binding Buffer.
• Perform a western blot to determine if a His-tag is present.
• Consider making a new construct or choosing a different E. Coli expression strain.

Protein eluate is not pure

Wash volume is not sufficient

• Increase the wash volume.

Concentration of imidazole is too low

• Increase the concentration of Imidazole in the wash buffer up to 15mM.