(11f) Exploring Interfacial Behavior of Viruses and Proteins in Osmolyte Solutions

Osmolytes are well-known for their ability to stabilize biomolecules. Common osmoprotectants are naturally occurring and biocompatible and are represented by amino acids and derivatives, amine oxides, and polyhydric alcohols. The mechanisms of biomolecule stabilization are not clear. It is possible that the water structure changes around the biomolecules, without direct interaction of the osmolyte and the biomolecule. Another possibility is that direct binding to the protein backbone may cause conformational changes and stability. Our studies explore the effect of osmolytes on virus and protein at different interfaces to understand the differential interaction behavior. Moreover, these studies indicate the efficiency of different class of osmolytes. The underlying hypothesis is that the viral particles are structurally more rigid than small proteins and therefore demonstrate different behavior in the presence of osmolyte.

Behavioral differences of many different viruses and proteins were studied to better understand the intraparticle, interparticle, and interfacial interactions using a variety of systems. One system we studied was the partitioning of viral particles in an aqueous two-phase system comprised of PEG and citrate. Virus partitioned to the PEG-rich phase and was rarely found in the citrate-rich phase. When osmolytes were added to the system, less PEG and citrate were needed to salt out the virus from the citrate-rich phase and pull the virus into the more hydrophobic PEG-rich phase. This likely occurred because the osmolyte, which remained in the salt-rich phase, was able to change the water structure in the salt-rich phase and cause salting out due to the increased osmotic strength, not the ionic strength. It was found that glycine was best at increasing virus in the PEG-rich phase, followed by betaine and TMAO. This demonstrated that the interfacial interactions of viruses changes in the presence of osmolytes. In a similar study, high osmolyte concentration in a single-phase system resulted in the flocculation of viral particles. Osmoprotectants glycine, betaine, and TMAO resulted in interparticle viral flocculation and an increased interfacial contact, again likely due to the change in water structure and a dehydration of the viral surface. The results showed increased interparticle interactions in the order: glycine > TMAO > betaine. These studies indicate different osmolyte classes have varying effects on the first virial coefficient, referring to the interfacial interaction between virus and dispersed phase in the biphasic system, and the second virial coefficient, referring to virus-virus interparticle interaction in the single-phase system. Moreover, these studies provide insights into how glycine, betaine and TMAO act as osmoprotectants.

Another study focused on the effect of similar osmolytes on the assembly of viral capsid proteins during the virus infection cycle to demonstrate the preferential interparticle and intraparticle interactions. The results demonstrated that osmolytes stabilized progeny viral capsid proteins in the host cell, thus inhibiting capsid assembly. The failure to synthesize the infectious progeny virions likely indicates that the intraparticle interactions in the capsid proteins were more prominent than interparticle interactions in presence of the osmolytes. Similar behavior was observed for the host cell proteins in the single and biphasic systems. The results indicated the potential of osmolytes as antiviral compounds by reducing intraparticle interactions to disrupt the viral infection cycle.

Overall, these studies give insights into the different actions of osmolytes on the interfacial behavior of viruses and proteins in various environments to develop viral-based biotherapeutic processing and biomedical technologies.