How to Increase Soluble Protein Expression

How to improve protein solubility

To answer this question, we should know what factors contribute the protein solubility. For a particular protein, the electrostatic charge plays an important role in its solubility. For different proteins, the protein production processes also affect the solubility of particular protein.

The isoelectric points has the effects on protein solubility. Proteins are comprised of amino acids which interact with solution, like water. There is a technology known as isoelectric focusing, which can separate the proteins of protein mixtures. A mixture is placed in a polyacrylamide gel that has a pH gradient. An anode (positive electrode) and a cathode (negative electrode) are positioned at the low and high ends of the pH gradient, respectively. If a protein is located in the high pH region, it will be negatively charged and will move toward the anode. As the protein moves to a lower pH region, its surface charge will become less negative, and a pH region will be reached at which the protein net charge is zero (the isoelectric point). The protein will stop moving and, because different proteins have different isoelectric points, separation can be achieved.

The protein production processes also affect the solubility of particular protein. Simultaneous addition of charged amino acids L-Arg and L-Glu at 50 mM to the buffer can dramatically increase the maximum achievable concentration of soluble protein (see to “A Simple Method for The growth medium Improving Protein Solubility and Long-Term Stability”).

From other researches, we can know the following factors also affects the protein solubility,

• Factors which affect the rate of protein synthesis, like growth temperature, promoter type, plasmid copy ability, inducer concentration.
• Growth medium.
• Co-expressed chaperones and/or foldases
• Cytoplasmic or periplasmic expression
• Specific host strains
• Fusion protein
• Expression System

Now, let's go to get soluble protein of interest.