Fig. 2: Conformational changes from the inactive, open-spiral to the active, closed-ring structures of the ssDNA-bound gp41 helicase.

Side views of (a) the open spiral and (b) the closed-ring structure. The domains are colored as in Fig. 1a. Subunits A–D are shown as gray surfaces. The NTDs and LHs of subunits E and F are in cartoon form and their CTD are shown in colored surfaces. Illustrations depict the scissor-like motion of the gp41 helical hairpins in (c) the inactive, open spiral and (d) the active, closed-ring structures. In contrast, illustrations depict the aperture-like swivel motion of the N-terminal helical hairpins of the E. coli DnaB helicase in (e) the inactive, open spiral and (f) the active, closed ring (PDB entries 6QEL and 6QEM). The red curves in (d) and (f) represent the lagging-strand DNA. Top surface views of (g) the gp41 helicase showing the bound ssDNA and ATPγS molecules (this study) and (h) the DnaB helicase showing the bound ssDNA and nucleotides (PDB entry 6QEM). The dashed triangles indicate the interdimeric and intradimeric location of the seam in (g) the T4 helicase and (h) the DnaB helicase, respectively. Created with BioRender.com.