Fig. 6: Structural rearrangements of Can1 upon cA4 binding in solution.
From: Structure and mechanism of a Type III CRISPR defence DNA nuclease activated by cyclic oligoadenylate
a Dimensionless Kratky plot of Can1 in the presence (blue) and absence (black) of cA4. Data were normalised with Rg and I(0) of 28.88 ± 0.13 Å and 1.090E-1 ± 1E-4 respectively for Can1 with cA4 and 30.26 ± 0.11 Å and 8.99E-2 ± 6.5E-05 respectively for apo Can1. Cross-hairs mark the Guinier-Krakty point or peak position for an ideal, globular particle. b Paired-distance, P(r), -distribution function performed as an indirect Fourier transform using the Moore method. P(r)-distributions were normalised to particle’s Porod volume using 121,421 Å3 and 132,291 Å3 for the Can1 with cA4 (blue) and apo Can1 (black), respectively. Widening of the distribution for apo Can1 suggests larger distances are more accessible. c Fit of apo Can1 SAXS data (black circles) using atomistic model from constrained torsion angle molecular dynamics. Best single-state model (red line), χ2 1.8, identifies a model that opens through translation of the nuclease domain. The best open model was achieved where the CARF dimer was maintained as a rigid body and the nuclease-like domain was allowed to vary ± 5 Å from its observed position. The nuclease domain was treated as a separate, rigid body tethered by an unconstrained loop (residues 423 to 428). Residuals of the fit are presented. The inset shows the fit of the Can1 crystal structure (cyan) to apo-state SAXS data (black). d Surface representation of Can1 as predicted by SAXS in the absence of cA4 (left) (cA4 is shown to illustrate the binding position and demonstrates the CARF domains are immobile) and the structure of Can1 in complex with cA4 solved by X-ray crystallography (right). Coloured as first CARF domain (magenta), nuclease-like domain (cyan), second CARF domain (green), nuclease domain (orange). Loops between the domains are not shown for clarity. A molecule of cA4 bound to Can1 is shown in yellow spheres. e The crystal structure of Can1 shown in cartoon form coloured by temperature factor from white (high temperature factor) to dark purple (low temperature factor). A molecule of cA4 bound to Can1 is shown in yellow spheres.
