Concentration and separation of proteins using polyion condensates*

When oppositely charged macromolecules are mixed in aqueous systems at the right conditions, i.e., ionic strength, mixing ratio, pH, etc., solutions phase separate in a condensed phase which is rich in macromolecules and a dilute phase. The so formed polyion condensate can be liquid-like or solid-like. In both cases proteins can be captured in the condensate phase. This protein partitioning strongly depends on the ratio between the oppositely charged macroions.
The cellular fluids contain liquid-like domains with similar properties to polyion condensates. This is not surprising since these cellular structures consist of intrinsically disordered proteins (IDPs) which are zwitterionic in nature, these readily phase separate in vitro, or contain RNA, which is negatively charged, and IDPs with high amount of basic residues. These cellular condensates are expected to selectively partition other biomacromolecules.
Cellular condensates are very complex multi-component systems, which can be mimicked using simple polyion condensates, consisting of synthetic oppositely charged polyelectrolytes. In this talk I will discuss two features of these polyion condensates which can be linked to the cellular condensates. First of all their ability to concentrate proteins and second that the partitioning of proteins can be very selective. This selectivity can be used to separate two types of proteins. Both these features are also important for extraction processes in chemical engineering. This talk will therefore conclude by discussing the possibility to use these condensates as tunable extraction media for biorefinery applications.