Structure Biology Study Of Bunyavirus Ribonucleoprotein Complex

Bunyaviruses are the causative agents of serious human disease with high infection,worldwide distribution and high fatality. Lots of them are the most improtant pathogenof human, for example, Crimean-Congo hemorrhagic fever virus (CCHFV) and severefever with thrombocytopenia syndrome (SFTSV) both belonged to Bunyaviruses.The genomes of Bunyaviruses are featured by three segments negative-sense RNA,termed L (the large segment), M (the middle segment), and S (the small segment). TheL encodes for L protein, the RNA-dependent RNA polymerase (RdRp). The M encodestwo surface glycoproteins (Gn and Gc). The S encodes a nucleocapsid protein (NP). Invirus life cycle, The nucleocapsid protein (NP) of Bunyaviruses facilitate genomic RNAencapsidation and form RNP with RdRp responsible for virus transcription andreplication. In Bunyavirus family, nucleocapsid proteins significantly differ from eachother. For example, the molecular weight of CCHFV NP is52kDa, Hantavirus NP is42kDa, but Bunyamwera virus (BUNV) NP is25kDa. So, we want to explore thedifference of the structure and potential biology function of the smallest BUNV NP andthe largest CCHFV NP by X-ray crystallography and electron microscopy (EM).In this paper, we solved the three-dimensional crystal structure of BUNV NP-RNAcomplex tetramer. Based on the structure, the RNA-binding site crevice located at theinterface of the N lobe and C lobe with large positively charged. The additionalN-terminal and a C-terminal extension participate in oligomerization with adjacent twoprotomers. Combine with the EM data, it provides the structure basis of mechanism ofBUNV RNP formation.Based on our previous study, we have identified and separated CCHFV NPoligomer. We also reconstruct its three-dimensional architecture by EM and it defininghow head and stalk domain interact for NP multimerization. This structure alsosuggested that both head and stalk domains may participate in viral genomeencapsidation. This work gives insight into the mechanism of the formation of CCHFVRNP.