Coronavirus nucleocapsid proteins assemble constitutively in high molecular oligomers

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

Using pull-down experiments and density glycerol gradients, our study provides additional evidence that CoV N proteins oligomerize. Several structural biology studies have indicated that SARS-CoV N protein dimerizes through the N2b/CTD domain 22, 24, 27, 32, 36 and it is generally accepted that the dimerization of N2b/CTD domain serves as the basic building block for CoV ribonucleoprotein virion core formation through multimerization 15, 46, 47 . We and others, however, have already pointed out that the N-terminal N1b/NTD and N3 regions could also interact with full length of MHV N protein 11, 19 . Our data extends and completes the information acquired by these investigations as we found that at least three areas of MHV N protein, i.e. N1a-N1b, N2a and N2b-N3, mediate its self-interaction. Importantly, those domains can bind reciprocally between themselves (Fig. 3 ) and our findings provide a possible model for MHV N protein oligomerization, i.e. a single N molecule appears to have several binding sites that allow the association of multiple N protein units to a single oligomer. However, we cannot exclude that binding promiscuousity and affinity of the various N protein domains, which we have investigated using truncated proteins, are more limited and different, respectively, in the context of the full-length protein.