Crystal structure of glycoprotein C from Rift Valley fever virus

Rift Valley fever virus (RVFV), like many other Bunyaviridae family members, is an emerging human and animal pathogen. Bunyaviruses have an outer lipid envelope bearing two glycoproteins, GN and GC, required for cell entry. Bunyaviruses deliver their genome into the host-cell cytoplasm by fusing their envelope with an endosomal membrane. The molecular mechanismof this key entry step is unknown. The crystal structure of RVFV GC reveals a class II fusion protein architecture found previously in flaviviruses and alphaviruses. The structure identifies GC as the effector ofmembrane fusion and provides a direct view of the membrane anchor that initiates fusion. A structure of nonglycosylated GC reveals an extended conformation that may represent a fusion intermediate. Unanticipated similarities between GC and flavivirus envelope proteins reveal an evolutionary link between the two virus families and provide insights into the organization of GC in the outer shell of RVFV.