Figure 1.
Figure 1. The X-ray crystal structure of D. rerio secretagogin.
A: Secretagogin monomer consists of six EF-hand motifs arranged
in pairs to form three globular domains (rendered consecutively
in red, yellow, and cyan). Linkers L1 and L2, highlighted in
green, connect the individual domains. The apposed metal binding
loops form antiparallel -sheet
on the outer surface of the V-shaped molecule. The helices of
the individual EF-hand motifs are labeled for clarity. B: A
stereo view of C -trace
of the superposed domains I, II, and III (red, yellow, and cyan,
respectively) of secretagogin. The topologically equivalent
motifs EF1, EF3, and EF5 overlap well, except for the
Ca^2+-binding loop which adopts the open, Ca^2+-ready
conformation
in EF5-hand (cyan arrow) and closed, Ca^2+-free
conformation
in EF1 and EF3 motifs. The EF2 hand differs from all the
remaining EF-hands due to a break at Met63 in the helix E2 (red
arrow). C: A stereo image of the calcium-binding loop in
EF5-hand motif of D. rerio secretagogin. A final 2mF[o]-DF[c]
electron density map (blue mesh) is contoured at 1.2 level.
The refined protein model is shown in sticks. Residues of the
calcium-binding motif at positions 1 (Asp206), 3 (Ser208), 5
(Thr210), 7 (Ala212), and 12 (Glu217) are labeled for clarity. A
symmetry molecule of secretagogin from the crystalline lattice
contributes Lys138 (cyan sticks), which mimics the positively
charged calcium ion and stabilizes the loop in Ca^2+-ready
-like
conformation.
-sheet
on the outer surface of the V-shaped molecule. The helices of
the individual EF-hand motifs are labeled for clarity. B: A
stereo view of C 
-trace
of the superposed domains I, II, and III (red, yellow, and cyan,
respectively) of secretagogin. The topologically equivalent
motifs EF1, EF3, and EF5 overlap well, except for the
Ca^2+-binding loop which adopts the open, 
Ca^2+-ready
conformation
in EF5-hand (cyan arrow) and closed, 
level.
The refined protein model is shown in sticks. Residues of the
calcium-binding motif at positions 1 (Asp206), 3 (Ser208), 5
(Thr210), 7 (Ala212), and 12 (Glu217) are labeled for clarity. A
symmetry molecule of secretagogin from the crystalline lattice
contributes Lys138 (cyan sticks), which mimics the positively
charged calcium ion and stabilizes the loop in