Figure 5. Repositioning of the HRDC domain.

(A) Molecular surface representation of BLM-HD^ΔWHD (left) and the liganded complex (right) highlighting the relative positions of the HRDC domain (cylindrical helices coloured in pink). The HRDC moves from a ‘parked’ position located on one side of the helicase core, to an ‘engaged’ position on the other side in order to interact with the bound ssDNA-15mer. The N-terminus of the first HRDC alpha-helix is extended at the by ~6 aa, relative to the ‘parked’ position (as indicated by an arrow). (B) Molecular secondary structure cartoon highlighting interactions made by the HRDC to the bound ssDNA-15mer oligonucleotide. Side chains for key amino acid residues are shown in stick representation, with carbon atoms coloured according to their respective domains (see associated key). The bound ssDNA-15mer oligonucleotide is involved in interactions with both the D1 domain (carbon atoms coloured green) and the HRDC (carbon atoms coloured pink). Bound oligonucleotide is shown in stick representation, with carbon atoms coloured cyan.