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Figure 1.
Figure 1. Structure of cyanobacterial SmtB. (a) Sequence
alignment of Synechococcus SmtB and S. aureus CzrA, pointing out
the location of the proposed ligands to the a3N (red boxes) and
a5 (blue boxes) metal-binding sites.[16.] (b) Ribbon
representation of the structure of homodimeric apo-SmtB solved
to 1.7 Å resolution, with the side-chains of the proposed
ligands of one of the a5 metal sites indicated (see (a)).
Secondary structural units (N-a1-a2-a3-aR(a4)-b1-b2-a5-C) are
indicated for the gold-shaded protomer. In the gold-shaded
subunit, C-terminal residues 119-121, including zinc ligand
Glu120, are not visible in the electron density maps, indicative
of significant disorder in the absence of zinc. (c)
Superposition of apo-SmtB (green and gold-colored protomers)
with Zn[2] a5-SmtB (blue and cyan-colored subunits), the latter
solved to 2.3 Å resolution. The polypeptide chain could
not be traced from residues 92-97 in the blue-colored Zn[2]
a5-SmtB subunit. The Figure was generated by performing a
superposition of the C^a atoms of the a5 helices of the green-
and blue-shaded subunits of apo- and Zn[2] a5-SmtB,
respectively. This illustrates the large movement of the HTH and
b-wings of one subunit relative to the other, represented by a
movement of the Ser74 C^a atoms positioned toward the N terminus
of the aR helix by 4.8 Å. (d) Superposition of the
metal-binding residues in the apo- and Zn[2] forms of SmtB
derived from the superposition shown in Figure 1(c). Figures
were created using SPOCK: http://mackerel.tamu.edu/spock
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