High-resolution Crystal Structure of Dimeric VP40 From Sudan ebolavirus

Ebolaviruses cause severe hemorrhagic fever. Central to the Ebola life cycle is the matrix protein VP40, whicholigomerizes and drives viral budding. Here we present the crystal structure of the Sudan virus (SUDV) matrixprotein.Thisstructureishigherresolution(1.6A)thanpreviouslyachievable.Despitedifferencesintheproteinpurification, we find that it still forms a stable dimer in solution, as was noted forother Ebola VP40s. Althoughthe N-terminal domain interface by which VP40 dimerizes is conserved between Ebola virus and SUDV, the C-terminal domain interface by which VP40 dimers may further assemble is significantly smaller in this SUDVassembly.Keywords. Ebola virus; Sudan ebolavirus; VP40; matrix protein; virus budding.Ebolavirusescausehemorrhagicfeverinhumanswithupto 90% case fatality [1].There are 5 species in the genusof Ebolavirus,includingZaire ebolavirus (Ebola virus;EBOV) and Sudan ebolavirus (Sudan virus; SUDV).EBOV is the causative agent of the largest and ongoingoutbreak of Ebola hemorrhagic fever, in West Africa in2014 and 2015. SUDV shares approximately 70% aminoacid sequence identitywithEBOVand has caused5 out-breaks, including the second largest, which infected 425individuals in Uganda between 2000 and 2001 [2].Ebola virions are filamentous in shape and contain asingle strand of negative-sense RNA. The viral matrixproteinVP40isresponsibleforbindingtothehostmembrane and budding new virions from infectedcells [3,4].Indeed, VP40 alone is capable of assemblingand budding filamentous virus-like particles from cells,intheabsenceofanyotherviralmachinery[5–7].Inad-dition, VP40 has been shown to regulate viral replica-tion and transcription [8].VP40 exists in multiple structural states, including adimer, an RNA-binding octameric ring, and a rear-ranged hexamer [9, 10]. Rearrangement of VP40 intoone structure or the other is thought to confer multi-functionality, because each structure may drive a sepa-rate and essential biological function [9–11]. Of thesestructures, the VP40 dimer could be the precursor forbothotherstructures:theRNA-boundringandthema-trix forming filamentous assemblies [10].Better under-standing of the dimer structure could lead to improvedtemplates for drug design, against the dimer itself, oragainst sites in it that are required for the structural re-arrangement. A previous structure of the SUDV dimeris available at 1.83 A resolution [10], but in that struc-ture, several regions of the C-terminal domain (CTD)are disordered. Here we report a higher-resolution(1.6 A) crystal structure of the SUDV VP40 dimer inwhich additional regions of VP40 are now visualized.METHODS