Coronavirus nucleocapsid proteins assemble constitutively in high molecular oligomers

Cong, Yingying; Kriegenburg, Franziska; de Haan, Cornelis A. M.; Reggiori, Fulvio

Our attempts to narrow down the specific binding area within the various regions have been unsuccessful since it appears that the amino acids crucial for the N protein self-interaction are discontinuously distributed (Fig. 3) . The results obtained with the N2a truncation indirectly support this notion as a short domain will possess less key binding amino acids and consequently it will interact less pronouncedly compared to longer parts such as the N1 and N2b-N3 domains. Previous efforts to localize the residues essential to mediate SARS-CoV N2b-N3 (including the CTD) multimerization identified three different regions within this domain 22, 31, 34 , further underscoring the notion that discontinues binding regions, distributed over the entire N molecule, are responsible for the self-association. During the preparation of this manuscript, a cryo-EM analysis of ribonucleoprotein complexes isolated MHV virions was published and the model emerging from this work is consistent with our findings 48 . This study suggested that the N protein form octamers mainly via its CTD domain, which then further assembles into larger oligomeric structures that can acquire either a loose or a more compact intertwined filament shape 48 . In the proposed model, multiple surfaces of the N protein participate in the multimerization of the N protein octamer and this is coherent with our conclusion that several domains in the N protein mediate self-interaction.