Backrub changes for Ser/Thr vs. Asn/Asp α-Helix N-caps.

Distances are after superposition into the same reference frame using 4 Cαs (N-cap i−1 and i+1 to i+3).Distances for BRDEE for atoms at or beyond Cα i±1 are not shown (marked as “—”) because, by construction, those atoms are not moved by BRDEE.The signs of the backrub rotation angles and Δτ values are in terms of Ser/Thr→Asn/Asp.For average crystal structures, average sidechains (based on average Cβ positions and χ dihedral angles) were added in KiNG. The τ value used for each Δτ is an average across the crystal structure ensemble; this was preferable to measuring τ values directly from the average structures because the average coordinates before the i−1 Cα were unreliable due to variability within the crystal structure ensemble.For input to BRDEE, ideal sidechains were added in KiNG to ideal helices. The τ value used for each Δτ is taken directly from the lowest-energy computed structure.S/T HB and N/D HB are Ser/Thr and Asn/Asp H-bond lengths from the i sidechain O to the i+3 mainchain H. For crystal structures, an average ± standard deviation across the set of examples in this data set is given. For BRDEE, the value is taken directly from the final model.