Fig. 4. Normalized histograms of N–H⋯O HB (left) and O–H⋯O HB (right) angles (in °) for Ser–Asn (top) and Tyr–Asn (bottom) residue pairs from X-ray crystal structures. All histograms have 10° bin widths. The structure insets depict the HB angle on representative protein structure sidechains with the corresponding Cα of the residues represented as a green sphere and the remaining atoms shown as sticks with carbon in gray, hydrogen in white, nitrogen in blue, and oxygen in red.