In what form is GFP most commonly expressed for purification?

Green Fluorescent Protein (GFP) is most commonly expressed as a fusion protein with a tag to facilitate purification. This approach utilizes the fusion partner, which often includes an affinity tag like His-tag or GST, to simplify the isolation and purification of GFP from a complex mixture of proteins. The affinity tag allows for selective binding to a specific column during chromatography, making it easier to separate the target protein from other cellular components.

By using this method, researchers can achieve higher purity levels and greater yields of GFP, as the tag provides a highly specific interaction that can significantly enhance the purification efficiency. While GFP can exist as a standalone protein, the use of a fusion protein with a tag is considered standard practice in molecular biology for its advantages in purification processes, helping to streamline the procedure and improve overall results.

Additionally, expressing GFP as a soluble protein is valuable, but it does not specifically address the purification aspect, and dealing with insoluble protein aggregates often complicates purification due to their sedimentation and less favorable extraction conditions. Therefore, utilizing a fusion tag is the most effective and efficient strategy for GFP purification.