Figure 2.

Examples of MERA-derived ϕ/ψ distributions for well-ordered residues K4 (A,C) and K31 (B,D), using experimental input data (A,B), and ideal simulated input data (C,D), with the corresponding reference backbone torsion angles (PDB entry 2OED) (Ulmer et al. 2003) marked “×”. The surface area of each circle is proportional to its voxel population, and the color of each circle reflects its fractional deviation from that seen in the coil database. The bottom panels show plots of χ² as a function of S, obtained for values of θ of (from left to right) 0, 0.1, 0.2, 0.4, 0.8, 1.6, 3, 6, 10, 20, and 40. The horizontal error bars in the lower panels reflect the lack of convergence of the simulated annealing protocol, seen for very low,θ values. The value θ = 0.4 is used for deriving the populations in the upper panels. For all analyses, the diffusion anisotropy parameter, k, was set to zero and σ(q) values recommended for folded proteins in Table 1 were used. χ² values when using the database distributions (S=0) are 7.2 (K4) and 10.8 (K31). Green boxes mark secondary structure regions: β, PPII, α_L, type I β-turn (β−I) and α_R (see green labels in A). Experimental input data for K4 and K31 include all six types of J couplings (³J_HNHα, ³J_C′C′, ³J_C′Hα, ¹J_CαHα, ²J_NCα and ¹J_NCα), three types of chemical shifts (¹⁵N, ¹³C^α, and ¹³C′), and three types of short-range ¹H-¹H NOEs.