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Isoelectric Point

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Creative Biolabs has established a series of platforms to characterize the therapeutic protein candidates. The isoelectric point (pI) of a protein is one of many important parameters to predict protein correct folding condition during the manufacturing process. The pI is the pH at which the protein has zero net electrical charge and highly depends on the amount and type of amino acid residues in the protein, their solvent accessibility and spatial arrangement. The isoelectric point is predicted from the amino acid sequence with the assumption of its denatured form. It is well known that the predicted isoelectric point differs from the measured one, and a relationship between these two values can be calculated.

Isoelectric Point

If a protein solution is at a pH equal to this protein’s pI, the repulsive electrostatic forces between charges on the nearby protein molecules are minimized, resulting in the risk increase of the hydrophobic surface patches. These sites easily become aggregation hot spots. In most cases, antibodies have a pI above pH8.0 to fit our standard purification process. Antibodies with lower isoelectric points can affect the second step of purification process, with utilization of anion exchange chromatography and possibly increase the scope of the purification process. Successful samples with shifting the formulation pH away from the pI of a protein has shown to improve the protein’s stability. pI of an antibody can be modulated by protein engineering.

Normally the isoelectric point of a protein is calculated from its amount of charged residues in the primary amino acid sequence, utilizing EMBOSS pKa values. Since all the residue charges are taken into account, this calculation method reflects the denatured form of protein more than correctly folded form. Creative Biolabs guarantees that the predicted values are accurate to within 1 pH unit.




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