Figure 4.

Structure of the PARN RRM:cap complex and NMR dynamics studies for PARN RRM in the presence and absence of the m⁷GpppG cap analog. (A) Stereo view illustrating a trace of the backbone atoms for the ensemble of the 20 structures of the PARN RRM:cap complex (residues 436–512). Residues in β-strands, αA and αB and αC are colored green, orange and red, respectively. The aromatic side chain of W468 is also depicted in green. The cap analog is colored yellow and cyan for m⁷Gp and GDP (ppG), respectively. (B) Enlarged view of the interface between PARN RRM and the cap analog. Intra- and inter-molecular NOEs that were observed in NOESY spectra and used as restraints in the structure determination are displayed with cyan and magenta lines, respectively. The surface of the PARN RRM is shown using the same color-code as in Figure 2D. (C) Diagram of the interactions between the m⁷GpppG cap analog and PARN RRM. Dashed lines indicate hydrogen bonds. Wavy lines symbolize stacking interactions. (D) NMR dynamics studies for PARN RRM with and without the cap analog. ¹⁵N R₁ (top) and ¹⁵N R₂ (middle) relaxation rates, and steady-state ¹H–¹⁵N NOE values (bottom) are shown for free PARN RRM (blue) and the PARN:RRM complex (red). β-strands, helices, loops and turns are indicated schematically.