The mechanism of SARS-CoV-2 nucleocapsid protein recognition by the human 14-3-3 proteins

The coronavirus nucleocapsid protein (N) controls viral genome packaging and contains numerous phosphorylation sites located within unstructured regions. Phosphorylated SARS-CoV N was shown to bind to the host 14-3-3 protein in the cytoplasm. Proteomic data indicate that seven human 14-3-3 proteins are highly abundant in human tissues vulnerable to SARS-CoV-2 infection, collectively reaching ~1.8% of all proteins in the lungs, ~1.4% in the gastrointestinal system, ~2.3% in the nervous system. Although the association between 14-3-3 and SARS-CoV-2 N proteins can represent one of the key host-pathogen interactions, its mechanism and the specific critical phosphosites were unknown. Here, we show that phosphorylated SARS-CoV-2 N protein (pN) dimers, reconstituted via bacterial co-expression with protein kinase A, directly associate, in a phosphorylation-dependent manner, with the dimeric 14-3-3 protein hub, but not with its monomeric mutant. We demonstrate that pN is recognized by all seven human 14-3-3 isoforms with various efficiencies and determine the apparent KD to selected isoforms in a low micromolar range. Serial truncations pinpointed a critical phosphorylation site to Ser197, located within the SR-rich region of N. The tight 14-3-3/pN association suggests it could regulate nucleocytoplasmic shuttling of N, while hijacking cellular pathways by 14-3-3 sequestration. As such, the assembly may represent a valuable target for therapeutic intervention.