An aqueous anonic/nonionic surfactant two-phase system in the presence of salt. 2. Partitioning of ice structuring proteins

Abstract

Three ice structuring proteins (ISPs) with different molecular weights and net charges at pH 7.4 were partitioned in an aqueous anionic/nonionic surfactant two-phase system of SDS and Trition X-114 in the presence of 100 mM sodium chloride. The effects of temperature and SDS concentration on the protein partition coefficients were investigated. It is found that the protein partition coefficients increase with the increase of temperature and SDS concentration. Compared to the reported net dependence of protein partitioning in aqueous mixed surfactant two-phase systems, the observed protein partitioning behavior is driven primarily by excluded volume interactions between the proteins and the surfactant aggregates, rather than electrostatic interactions. Specifically, the ISPs partition preferentially to the micelle-poor phase, where they experience less excluded-volume interactions with the surfactant aggregates. The improvements in protein partitioning to the micelle-poor phase upon the SDS addition appear to result from the growth of the surfactant aggregates by forming mixed micelles, which enhances the excluded-volume interactions between the proteins and the surfactant aggregates.