This recombinant HCoV-NL63 E protein is produced using a cell-free in vitro expression system in E. coli. In this system, protein synthesis occurs in vitro using extracts from whole cells compatible with translation. These extracts contain all the necessary molecules and enzymes for transcription, translation, and post-translational modifications of the recombinant protein. With the addition of supplemental cofactors, E protein synthesis can be achieved within a few hours. However, this system may not be suitable for large-scale protein production. The advantages of this system include the ability to synthesize proteins without cell culturing and the potential to express multiple proteins simultaneously.
The HCoV-NL63 E protein is a small, integral, structural membrane protein embedded within the lipid envelope of mature viral particles. It plays crucial roles in various stages of the viral life cycle, including assembly, budding, envelope formation, and pathogenesis. The absence or inactivation of E protein leads to attenuated viruses, likely due to alterations in virion morphology or tropism. While the E protein is abundantly expressed inside infected cells during replication, only a small fraction is integrated into the virion membrane. The majority of the E protein is found in intracellular trafficking sites, such as the ER, Golgi, and ERGIC, where it assists in HCoV-NL63 assembly and budding. The E protein also plays a significant role in viral production and maturation.