Structural studies of yellow fever virus helicase

Yellow fever virus (YFV) is a pathogen of the flavivirus family. NS3, one of seven viral replicase proteins, has a protease domain and a helicase domain. The helicase is thought to separate plus and minus strands following replication. Helicase from YFV and WNV (West Nile virus) have been produced in E. coli and purified. ATPase activity of these recombinant helicase constructs has been demonstrated. YFV helicase has been crystallized. Crystals of active, recombinant YFV helicase diffract to 1.8 A. The crystal structure was solved by MAD. YFV helicase is organized in three domains. The first two domains are used for ATP binding and hydrolysis, and contain the seven sequence motifs characteristic of 'superfamily 2' (DEAD/DEAH box) helicases. A third domain functions in RNA binding. Hepatitis C virus (HCV) helicase is the nearest relative of known structure. YFV and HCV helicases are very similar in their NTPase domains. The third domain of YFV helicase is substantially different than the HCV helicase third domain. A structure of YFV helicase complexed with ADP has been determined to 2.6A. The complex structure reveals a similar binding of nucleotide substrate as other helicases of superfamilies 1 and 2. The structure of YFV helicase is used to characterize an internal cleavage within the NS3 helicase region and relationship with its viral partners including the protease cofactor NS2B and the viral RNA-dependent RNA polymerase NS5.