Figure 2: Structural characterization of the cpSRP43–A3CT complex.

(a) Crystal structure of cpSRP43 CD2CD3 (blue) with bound A3CT IV (salmon) as part of the fusion construct with thioredoxin (not shown). (b) The electrostatic surface potential of CD2CD3 is shown with positive charges in blue and negative charges in red (contoured at±5 kT). (c) ConSURF analysis showing the degree of conservation mapped on the surface of the CD2CD3 structure. Highly conserved residues are represented in dark red, partially conserved residues in magenta and less conserved residues in cyan. (d) Crystal structure of cpSRP43 CD3 in the open conformation with an unstructured ‘β2a’ strand. CD3 is stabilized by helix swapping between two CD3 molecules. (e) Solution structure of cpSRP43 CD3. A superposition of the 10 lowest energy structures is shown. (f) Close-up view of CD3 bound to A3CT IV highlighting the gap between strands β4 and β1′ induced by a helical turn (green) and forming the cage for substrate recognition. The increased β-sheet twist in the β-barrel, resulting in the loss of strand ‘β5’ is indicated (50°).