(515w) A Colloid-Inspired Approach to Virus Processing Based on Protein-Protein Interaction

The interactions between protein molecules and other solutes determine the thermodynamics of a protein solution (Curtis and Lue, 2006), which in turn is the key factor in designing and optimizing a bioprocess relying on the correct reaction pathways of the protein molecules to form active complexes. Knowledge of the precise nature of these interactions, and how they are affected by physico-chemical conditions such as pH, temperature and ionic strength is therefore crucial. Use of the osmotic second virial coefficient (SVC) to probe protein-protein interactions has been proven successful to model and predict the likelihood of protein crystallization (George et al., 1997), protein aggregation during refolding (Ho et al., 2003) and protein formulation (Chi et al., 2003). In this work, we researched a similar approach to understand fundamentally the formation of virus-like particles (VLPs). VLPs are functional architectures formed from the self-assembly of viral structural proteins that have been proven to be safe and highly immunogenic. Recently, VLPs have been developed as a vaccine against cervical cancer by Merck (West Point, PA, USA), and have also been shown in animal studies to provide protection against both seasonal and avian influenza following intranasal administration (Novavax, Rockville, MD, USA). To better understand the mechanism underpinning the self-assembly of VLPs, the interactions between the assembling viral structural proteins were inferred from measurement of the SVC using static-light scattering, which provided information on the magnitude and direction of the interactions involved. We observed that the onset of self-assembly triggered by the addition of calcium ions and lowering of solution pH was accompanied by a significant increase in attractive force between the structural proteins. This was indicated by a substantial and negative shift of the SVC. This is the first time that the self-assembly of VLPs has been related to measurement of the SVC. The osmotic second virial coefficient is a thermodynamic parameter that reflects changes in electrostatics, van der Waals interactions, hydration forces, and hydrophobic effects. Understanding of how the SVC of the structural proteins is influenced by the solution conditions provides important clues for the design and optimization of VLP processing in a cell-free reactor.

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