How to restore the activity of proteins frozen at -80°C?

In the laboratory, proteins are typically stored at extremely low temperatures (such as -80°C) to minimize degradation and maintain their activity. When these proteins are needed for use, the correct thawing steps are crucial for the recovery of their activity. Here are some steps and considerations to help ensure that proteins retain their original functional characteristics as much as possible after thawing.

 

I. Slow Thawing

1. Transfer the frozen protein samples from −80°Cthe -80°C storage to a 4°C refrigerator to thaw slowly, which usually takes several hours.

2. Avoid thawing directly at room temperature to reduce protein denaturation due to sudden temperature changes.

 

II. Use Suitable Buffer

1. Ensure that cryoprotectants (such as glycerol, trehalose, or DMSO) and appropriate buffer systems (such as pH-stable Tris or PBS) are used during protein freezing.

2. If the protein needs to be re-diluted or dialyzed, use a buffer system suitable for its activity recovery.

 

III. Avoid Repeated Freeze-Thaw Cycles

1. Thaw only the necessary amount each time to avoid protein aggregation or inactivation caused by multiple freeze-thaw cycles.

2. If possible, aliquot samples to reduce freeze-thaw cycles.

 

IV. Check and Adjust Environmental Conditions

1. pH and Ionic Strength: Protein activity is sensitive to pH and salt concentration; adjust to optimal conditions using dialysis or dilution after thawing.

2. Add Cofactors: Some enzymatic proteins may require metal ions or cofactors to restore activity.

 

V. Gentle Mixing

Gently invert or slowly vortex the samples to avoid mechanical shear force damage to the protein.

 

VI. Test Activity

1. Perform activity tests immediately after thawing to confirm whether the protein function is intact.

2. If activity is found to decline, try adding stabilizers (such as BSA) or adjusting sample concentration to improve stability.

 

VII. If Aggregation or Inactivation Issues Arise

Use the following strategies:

1. Dialysis: Remove cryoprotectants that may affect protein activity during freezing.

2. Ultrasonication or Centrifugation: Remove aggregated protein fragments.

3. Refolding Methods: Use denaturation-renaturation buffers (such as urea or guanidine salts) for refolding.

 

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