Da Yu Protein Sciences – Protein Solubility
Low protein solubility can be problematic. It can present a significant obstacle to protein formulation for parenteral drug administration. A selected mutagenesis approach may increase protein solubility but may alter other protein properties or lead to unwanted effects such as increased immunogenicity or altered bioavailability. Instead, an empirical approach, such as screening different environmental parameters for their influence on solubility, may be a more effective strategy.
PEG-Mediated Protein Precipitation - Polyethylene glycol (PEG) is an inert ccompound that quantifiably decreases a protein’s solubility. Increasing PEG concentrations cause protein solubility to decrease exponentially and the protein precipitates. Plotting the amount of protein remaining in solution versus the PEG concentration yields a sigmoidal protein solubility curve. The inflection point
of this curve is the PEG concentration that reduces the protein concentration by 50% and is known as the PEGmidpt. The PEGmidpt can be used to screen pH, buffers, or excipients to assess their effect on a protein’s solubility. An excipient screen can then be followed by producing protein solubility curves for individual excipients of interest. Excipients that increase a protein’s solubility will have their protein solubility curve shifted to the right and yield a higher PEGmidpt.
A logarithmic transformation of the linear portion of the protein solubility curve allows extrapolation to a theoretical maximum protein concentration in the absence of PEG. In this way, one can obtain an estimate of the increased solubility achieved by a given excipient, or other environmental parameter such as pH.
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