The Role of the Tyrosine-Based Sorting Signals of the ORF3a Protein of SARS-CoV-2 on Intracellular Trafficking, Autophagy, and Apoptosis.

Open reading frame 3a (ORF3a) encodes for the largest of the SARS-CoV-2 accessory proteins. While deletion of the ORF3a gene from SARS-CoV-2 results in a virus that replicates slightly less efficiently in cell culture, deletion also results in a virus that is less pathogenic in mouse models of SARS-CoV-2 infections. The ORF3a has been reported to be a viroporin, induces apoptosis and incomplete autophagy in cells. Thus, determining the domains involved in these functions will further our understanding of how this protein influences virus assembly and pathogenesis. Here, we investigated the role of the three potential tyrosine-based sorting signals in the cytoplasmic domain of the ORF3a on intracellular protein trafficking, apoptosis, and in the initiation of autophagy. Our results indicate that more than one YxxΦ motif is required for efficient transport of ORF3a, ORF3a expression resulted in minimal apoptosis, and cell surface expression was not required for autophagy.