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Introduction

In molecular biology and biochemistry, protein purification is a crucial process for isolating a specific protein from a complex mixture. One of the most commonly used techniques for purifying recombinant proteins is Nickel-NTA affinity chromatography. This method takes advantage of a special tag, usually a His-tag (a series of histidine residues), which binds specifically to a nickel ion immobilized on a resin. In this article, we’ll discuss how Nickel-NTA affinity chromatography works, why it’s used, and which tags are involved in this technique.

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What is Nickel-NTA Affinity Chromatography?

Nickel-NTA (Nickel-Nitrilotriacetic acid) affinity chromatography is a technique used to purify proteins that are fused with a hexahistidine (His6) tag. The His-tag consists of six histidine residues, which have a high affinity for nickel ions. The chromatography resin used in this method contains nickel ions, which can specifically bind to the histidine residues in the tag. When a mixture containing the recombinant protein is passed through the column, only the proteins with the His-tag will bind to the resin, while other proteins are washed away. The His-tagged protein can then be eluted by adding imidazole, which competes with the histidine residues for binding to the nickel.

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The Role of the Hexahistidine (His6) Tag

The His6 tag is one of the most commonly used tags in recombinant protein purification. It is made up of six histidine residues, which are added to the protein of interest. The tag is usually added at either the N-terminus or C-terminus of the protein, depending on the experiment’s requirements. The histidine residues interact strongly with the nickel ions on the chromatography resin, allowing for efficient binding and purification of the protein.

Once the protein has been bound to the Nickel-NTA resin, it can be eluted by increasing the imidazole concentration or lowering the pH, causing the histidine residues to release the protein from the nickel.

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Why Choose Nickel-NTA Affinity Chromatography?

Nickel-NTA affinity chromatography is preferred for several reasons:

1. High specificity: The interaction between histidine residues and nickel ions is highly specific, minimizing the binding of non-target proteins.

2. Efficient purification: The His-tag can be used for high-affinity binding, allowing for high-purity protein recovery.

3. Versatility: This method can be used with a variety of proteins, as the His-tag is small and typically does not interfere with protein function or structure.

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Which Tag Is Used in Nickel-NTA Affinity Chromatography?

In Nickel-NTA affinity chromatography, the recombinant protein is typically tagged with a hexahistidine (His6) tag. The six histidine residues bind to the nickel ions on the resin, enabling the purification of the protein.

Correct Answer

Given the options in the question, the correct answer is:

(c) Hexa-histidine

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Other Tags in Protein Purification

While the hexahistidine tag is commonly used with Nickel-NTA affinity chromatography, other affinity tags like Flag, Glutathione-S-transferase (GST), and Maltose binding protein (MBP) can also be used for recombinant protein purification. However, these tags are typically associated with different types of affinity chromatography, such as:

• Flag tag: Often used with Flag affinity chromatography.

• GST tag: Used with Glutathione affinity chromatography.

• MBP tag: Used with Maltose-binding protein affinity chromatography.

These tags work through similar affinity-based interactions but use different resins and binding mechanisms.

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Conclusion

Nickel-NTA affinity chromatography is an effective and widely used technique for purifying recombinant proteins, and the His6 tag is the most common tag used for this purpose. By understanding the role of the His-tag and how it binds to nickel ions on the chromatography resin, researchers can efficiently purify proteins of interest. While other affinity tags exist for different purification methods, hexahistidine remains a popular choice for protein purification using Nickel-NTA affinity chromatography.

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Answer:

The correct answer is:
(c) Hexa-histidine