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Figure 4.
(a) Structural superpositions. DHHN with Ca^2+ (slate) and
without (magenta), and ShhN with Ca^2+ (orange) and without
(yellow; PDB 1VHH^24) are shown as coils. Zn^2+ and Ca^2+ ions
are depicted as spheres. The close-up highlights loop
Lys88–Gly94. Glu90 and Glu91 (stick representation) change
conformation upon Ca^2+ binding. (b) The ShhN solvent-accessible
surface colored by residue conservation (Supplementary Fig. 5).
Hh binding loops of HHIP are shown in cyan. (c) Comparison of
ShhN–HHIP and DHHN–HHIP complexes. The ShhN surface is
colored orange. The Shh loop Lys88–Gly94, which is ordered
only in the Ca^2+-bound ShhN–HHIP, is highlighted in red. Hh
binding loops of HHIP are shown as coils (ShhN–eHHIP  N
with Ca^2+ in green; ShhN–eHHIP N
without Ca^2+ in blue; DHHN–eHHIP N
without Ca^2+: molecule 1 in yellow and molecule 2 in cyan). A
third ligand binding loop of HHIP (BL3) is observed in only one
copy of the DHHN–eHHIP N
asymmetric unit (dotted ellipse; see also Supplementary Fig. 9).
(d) Effects of Ca^2+ binding. ShhN–eHHIP N
complexes are shown as coils (with Ca^2+, in orange and green,
and without Ca^2+, in violet and blue). Spheres highlight
HHIP-Glu381 and Shh-Glu90. Shh loop Lys88–Gly94 is depicted as
a dotted line. (e) Comparison of the Shh–HHIP and Shh-CDON
(PDB 3D1M^26) complexes. Shh ligands are superimposed (HHIP,
green; CDON, blue; HHIP-complexed ShhN, orange; CDON-complexed
ShhN, red). Metal ions are depicted as spheres.
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