Novel insights into cryo-EM structure of African Swine Fever Virus

African swine fever virus(ASFV)is a giant and complex DNA virus that causes a highly contagious and lethal swine disease for which there is no vaccine available.Here we describe the cryo—electron microscopy(cryo-EM)structure of ASFV,the first virus(to our knowledge)that has been found to use two lipid membrane layers and two protein shells to encapsidate and protect its genome.Using an optimized image reconstruction strategy,we solved the AFSV capsid structure up to 4.1-angstroms,which is built from 17,280 proteins,including one major(MCP)and four minor capsid proteins(M1249 L,p17,p49 and H240 R),and organized into pentasymmetrons and trisymmetrons.The atomic structure of the MCP informs putative conformational epitopes,which determine the specific differences between the virus types,being valuable for epitope-focused immunogen design against ASFV infection.The minor capsid proteins form a complicated network below the outer capsid shell,stabilizing the capsid by holding adjacent capsomers together.Acting as core organizers,100-nm-length M1249 L proteins,running along each edge of the trisymmetrons and bridging two neighboring pentasymmtrons,form extensive intermolecular networks with other capsid proteins to guide the formation of capsid framework.These structural details unveil the basis of capsid stability and assembly,opening up new avenues for ASF vaccine development.