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New insights into the replication-transcription complex of coronaviruses

Hamburg. In a study of the Heinrich Pette Institute, Leibniz Institute for Experimental Virology (HPI), the replication-transcription complex (RTC) of coronaviruses was characterized in more detail using a mass spectrometric approach. The studies focused on the regulatory proteins nsp7 and nsp8 and their different complex formation in different Alpha- and Betacoronaviruses. The study results have now been published in the renowned journal Science Advances.

The two non-structural coronavirus proteins nsp7 and nsp8 interact with and regulate RNA-dependent RNA polymerase and other enzymes in the replication-transcription complex. However, the structural plasticity of the nsp7+8 complex in different coronaviruses is still under debate.

Based on methods of native mass spectrometry and complementary biophysical techniques, in the current publication the research team led by HPI Junior Research Group head Dr. Charlotte Uetrecht now presents the specific features of nsp7+8 complex stoichiometry and topology. The team analyzed nsp7+8 complexes from a total of seven different coronaviruses of the Alpha- and Betacoronavirus genera, including SARS-CoV-2.

The results show that the nsp7+8 complexes of the different coronaviruses can be divided into three groups: "They form either heterotrimers, heterotetramers, or both and exhibit different topologies. Moreover, even at high protein concentrations, mainly heterotetramers are observed for SARS-CoV-2 nsp7+8," explains Dr. Charlotte Uetrecht.

By comparing the different structures, the research team was also able to identify the amino acids that determine the assignment to these three groups.

"In summary, our results show the characteristic distribution of nsp7+8 complexes in representative Alpha- and Betacoronaviruses. Using our data as well as the sequence and structural analyses, we can propose a model that explains the composition of the different nsp7+8 structures. These findings help us to better understand the exact function and role of nsp7 and nsp8 in the RTC of coronaviruses," adds first author Dr. Boris Krichel.

The study was carried out in cooperation with researchers from the Giessen University, the European XFEL, the EMBL Hamburg and the ETH Zurich.

The results are published in the journal Science Advances:

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 (2021). Hallmarks of Alpha- and Betacoronavirus non- structural protein 7+8 complexes. Sci Adv. 2021 Mar 3;7(10):eabf1004.

Contact:

Dr. Charlotte Uetrecht:

Charlotte.uetrecht(at)leibniz-hpi.de  

Heinrich Pette Institute, Leibniz Institute for Experimental Virology,
Hamburg

Dr. Boris Krichel

Boris.krichel(at)leibniz-hpi.de

Heinrich Pette Institute, Leibniz Institute for Experimental Virology,
Hamburg

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