Table 1.

Intramolecular hydrogen^* bonding network^† observed at the helix–helix interior and at the turn region of the structure of HH21 (Fig. 3A)

Donor D	Acceptor A	Distance (Å) D–A	Distance (Å) H–A	Angle (°) D—H–A	Type
C2B	O17	3.441	2.39	163	SB/L/CHO
C5B	O14	3.507	2.52	152	SB/L/CHO
C5D2	O14	3.446	2.43	156	SB/L/CHO
C14B	O5	3.422	2.42	154	SB/L/CHO
C14D2	O5	3.473	2.47	153	SB/L/CHO
C17B	O2	3.535	2.57	147	SB/L/CHO
C17D2	O2	3.466	2.52	146	SB/L/CHO
C8B	O11	3.258	2.30	147	SB/T/CHO
N10	C14R‡	3.611	2.67	152	BS/T/NHπ
N11	O8	3.014	2.01	164	BB/T/NHO

SB/L/CHO: Side chain to backbone lateral (interhelix) hydrogen bond (C—H—O). BB/T/NHO: Backbone to backbone turn stabilizing hydrogen bond (N—H—O). SB/T/CHO: Side chain to backbone turn stabilizing hydrogen bond (C—H—O). BS/T/NHπ: Backbone to aromatic ring center of the side chain interaction (N—H—π) at the turn region. 

^*Normalized values (30, 31). 

^† Helix stabilizing 4 → 1(N—H—O) hydrogen bonds are not shown (see Table 3). 

^‡ C14R is the pseudo atom at the ring-center of the side chain of the residue ΔPhe14.