Extended Data Fig. 1: Evaluation of peptide bond geometry.
From: Cryo-EM model validation recommendations based on outcomes of the 2019 EMDataResource challenge
All 63 Challenge models were evaluated using MolProbity. APOF and ADH each have one cis peptide bond per subunit before a proline residue. (a) Counts of peptide bonds with each of the following conformational properties: cisP: cis peptide before proline, twistP: non-planar peptide (>30°) before proline, cis-nonP: cis peptide before non-proline, twist-nonP: non-planar peptide bond before non-proline. Incorrect cis-nonP usually occurred where the model was misfit (see Extended Data Figs. 2 and 3), while incorrect cis or trans Pro usually produced poor geometry. Values inconsistent with reference models are highlighted. Statistically, 1 in 20 proline residues are genuinely cis; only 1 in 3000 non-proline residues are genuinely cis, and strongly non-planar peptide bonds (>30°) are almost never genuine28. Models are identified by the submitting group (Gp #, group id as defined in Table 1), model number (some groups submitted multiple models), and Target (T1-T3: APOF, T4: ADH). Optimized models are shaded blue. Only two groups (28, 31) had all peptides correct for all 4 targets. Models illustrated in panels b-d are indicated by labeled boxes. (b) Correct cis peptide geometry for Pro A62 in two ADH models. (c) Incorrect trans peptide geometry, with huge clashes up to 1.25 Å overlap (clusters of hot pink spikes), 2 CaBLAM outliers (magenta CO dihedral lines), and poor density fit. (d) Incorrect trans peptide geometry, with huge 1.9 Å Cβ deviation at Leu 61 (magenta ball) because of incorrect hand of Cα, and 2 CaBLAM outliers. Molecular graphics were generated using KiNG.
