Viruses can be divided into enveloped viruses (e.g., rabies virus) and non-enveloped viruses. Non-enveloped viruses only consist of the capsid protein and the viral genomic nucleic acids. They are generally homogenous in structure and easy to separate and purify. The enveloped viruses on the other hand, haves complicated structure and heterogeneity.
Enveloped viruses generally have a linear DNA or RNA in the inner core of the viral particles. The inner core is surrounded by a capsid, which is comprised of multiple nucleoprotein subunits. Together, the inner core and the capsid form a tightly-packed nucleocapsid particle. The nucleocapsid particle is wrapped by a lipid envelop on which one or more than one outer membrane protein is located. Each outer membrane protein has multiple copies on the surface and is densely distributed on the surface of the virus. The one or more outer membrane proteins are generally glycosylated to certain degree.
Current methods of purifying enveloped virus (e.g., rabies virus) are mainly based upon the different molecular sizes between the virus particle and impurities, for example, by using density gradient ultracentrifugation and/or gel filtration chromatography. However, impurities having a similar size as the viral particles cannot be separated by these methods. Therefore, there is a need for new methods of purifying enveloped viruses (e.g., rabies virus).
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