Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.09.30.320762v1?rss=1 Authors: Krichel, B., Bylapudi, G., Schmidt, C., Blanchet, C., Schubert, R., Brings, L., Koehler, M., Zenobi, R., Svergun, D., Lorenzen, K., Madhugiri, R., Ziebuhr, J., Uetrecht, C. Abstract: Coronaviruses infect many different species including humans. The last two decades have seen three zoonotic coronaviruses with SARS-CoV-2 causing a pandemic in 2020. Coronaviral non-structural proteins (nsp) built up the replication-transcription complex (RTC). Nsp7 and nsp8 interact with and regulate the RNA-dependent RNA-polymerase and other enzymes in the RTC. However, the structural plasticity of nsp7+8 complex has been under debate. Here, we present the framework of nsp7+8 complex stoichiometry and topology based on a native mass spectrometry and complementary biophysical techniques of nsp7+8 complexes from seven coronaviruses in the genera Alpha- and Betacoronavirus including SARS-CoV-2. Their complexes cluster into three groups, which systematically form either heterotrimers or heterotetramers or both, exhibiting distinct topologies. Moreover, even at high protein concentrations mainly heterotetramers are observed for SARS-CoV-2 nsp7+8. From these results, the different assembly paths can be pinpointed to specific residues and an assembly model is proposed. Copy rights belong to original authors. Visit the link for more info