Figure 2. NMR structure of CNBD bound to TRIP8b_nano.

(A) (Top) comparison of secondary structure elements of cAMP-free CNBD (Saponaro et al., 2014), cAMP-bound CNBD (Zagotta et al., 2003) and cAMP-free CNBD bound to TRIP8b_nano (this study). Secondary structure elements are indicated by arrows (β-strands) and cylinders (α-helices) and labeled. The loop between β₆ and β₇ constitutes the Phosphate Binding Cassette (PBC). The elements that fold upon binding of cAMP and TRIP8b_nano are shown in red. (Bottom) Chemical Shift Index (CSI, calculated using TALOS+) plotted as a function of the residue number of CNBD bound to TRIP8b_nano. Positive values represent helical propensity, while negative values represent strands. (B) Ribbon representation of the 10 lowest energy conformers of CNBD bound to TRIP8b_nano used for in silico modeling of CNBD - TRIP8b_nano complex. Secondary structure elements are coloured in light gray and labeled. Loop regions are colored in dark gray. The distal region of the C-helix (residues 657–662), which is unfolded in the free form of the CNBD (Saponaro et al., 2014) and folds upon TRIP8b_nano binding, is coloured in red. The unfolded regions at the N- and C-termini of the construct (residues 521–532 and 663–672 respectively) are omitted for clarity.