Hongliang Tian; Xiaoyun Ji; Xiaoyun Yang; Wei Xie; Kailin Yang; Cheng Chen; Chen Wu; Heng Chi; Zhongyu Mu; Zefang Wang; Haitao Yang

“ Based on structural homology, these residues of ZIKV helicase are likely to play similar roles in NTP hydrolysis. For instance, the side chain of K200 could be responsible for interacting with the γ-phosphate of the nucleotide during transition state stabilization; the strictly conserved D285 and E286 residues could participate in coordinating the divalent cation. In the overlaid structures, the base and ribose groups of AMPPNP bulge out from the binding pocket, implying that ZIKV helicase would lack nucleotide specificity for its NTPase activity. ”

“ The tunnel is lined with positively charged residues and remains wide enough to accommodate a single strand (ss) nucleic acid in an extended conformation running through Domain II to Domain I. The positively charged residues, most of which were contributed by Domain I and Domain II, presumably stabilize the sugar-phosphate backbone of the nucleic acid. Superposition of ZIKV helicase to DENV-4 helicase bound with a 12-mer ssRNA (PDB ID 2JLV) (Luo et al., [13] ) generated a model to analyze the potential pattern for nucleic acid binding. ”

“ Distinct from the DENV-2 helicase, whose two crystal forms both contain two molecules per asymmetric unit (Xu et al., [10] ) , ZIKV helicase has a solo protein molecule in an asymmetric unit in the crystals. No stable oligomer through crystallographic packing was identified in the crystals, consistent with the observation of a monomeric form of the ZIKV helicase in solution by size exclusion chromatography (Fig. 1A) . This observation suggests that ZIKV helicase is able to function as a monomer. The refined model is complete and includes the residues 175–617 from ZIKV NS3. ”

“ Haitao Yang and Hongliang Tian conceived and designed the experiments. Hongliang Tian, Xiaoyun Yang, Wei Xie, Heng Chi and Zhongyu Mu performed the experiments. Haitao Yang, Xiaoyun Ji, Cheng Chen, Chen Wu and Zefang Wang analyzed the data. Haitao Yang, Hongliang Tian, Xiaoyun Ji and Kailin Yang wrote the paper. Hongliang Tian, Xiaoyun Ji, Xiaoyun Yang, Wei Xie, Kailin Yang, Cheng Chen, Chen Wu, Heng Chi, Zhongyu Mu, Zefang Wang, and Haitao Yang declare that they have no conflict of interest. ”