Figure 2.

Prediction of Xaa-Pro peptide bond conformation from NMR chemical shifts by the program Promega. (A,B) Plot of the crystallographically observed ω angles, versus their probability score, P_cis, calculated by eq 5, (A) for residues that included ¹³C^γ chemical shift assignments, and (B) for all database residues with at least three out of four (¹³C’, ¹³C^α, ¹³C^β, ¹H^α) Pro assignments, and ignoring ¹³C^γ chemical shifts. Note that P_cis (eq 5) corresponds to a relative probability, i.e., P_cis = 0.5 refers to the case where the cis probability equals the average cis probability in the database (ca 5%). (C,D) Histograms of the normalized, true probability score $P_{\mathit{cis}}^{\mathit{norm}}$ , calculated by using eq 6 for Pro residues in the database in (C) the presence and (D) the absence of ¹³C^γ chemical shifts. The solid line in (D) corresponds to eq 6. Note that in the presence of ¹³C^γ chemical shifts the P_cis result is essentially binary, and the below unity value observed in the histogram for the highest P_cis bin largely reflects cases where solution and crystal structures differ.