A biocompatible surfactant, methyl ester sulphonate (MES), as a precipitating ligand for protein purification

- The use of MES as precipitating-ligand in surfactant precipitation is proposed.
- Precipitation level was a strong function of surfactant/protein molar ratio and pH.
- 54-56% and 83.3% activity recovery was obtained by solvent and TOMAC, respectively.
- Structural integrity of the lysozyme recovered was preserved.
- Better selectivity were exhibited compared to AOT.

A biocompatible surfactant, methyl ester sulphonate (MES), was evaluated in protein surfactant precipitation. The amount of lysozyme precipitated by MES was found to be a strong function of both the molar ratio of surfactant to protein (Rp), and pH. Precipitation increased proportionally with an increase in Rp up to an optimum of 16, where full precipitation was achieved, while with pH variations electrostatic interactions were found to be the main driver of precipitation. The precipitate was recoverable by solvent extraction (54-56% activity recovery by acetone, ethanol, 50% acetone/ethanol, and methanol), and counter-ionic surfactant, TOMAC (83.3% activity recovery at Rr = 1.5). Importantly, the structural integrity of the lysozyme recovered, either through solvent extraction or counter-ionic surfactant, was maintained, and this was confirmed by CD spectra and deconvolution. Precipitation with MES was compared to a conventional surfactant, AOT; in contrast with AOT, MES did not resolubilise the precipitate or cause structural transformations at higher Rps. MES exhibited better selectivity than AOT since it had minimal hydrophobic interactions in the absence of electrostatic interactions between the surfactant's anionic group, and the protein's positively charged groups (pH > pI). Hence, along with its economic benefits, and environmental features, this work has highlighted the potential of using MES in surfactant precipitation.