 |
PDBsum entry 2pq3
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Metal binding protein
|
PDB id
|
|
|
|
2pq3
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
A 1.3-A structure of zinc-Bound n-Terminal domain of calmodulin elucidates potential early ion-Binding step.
|
|
|
Authors
|
|
J.T.Warren,
Q.Guo,
W.J.Tang.
|
|
|
Ref.
|
|
J Mol Biol, 2007,
374,
517-527.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
|
|
|
Abstract
|
|
|
Calmodulin (CaM) is a 16.8-kDa calcium-binding protein involved in
calcium-signal transduction. It is the canonical member of the EF-hand family of
proteins, which are characterized by a helix-loop-helix calcium-binding motif.
CaM is composed of N- and C-terminal globular domains (N-CaM and C-CaM), and
within each domain there are two EF-hand motifs. Upon binding calcium, CaM
undergoes a significant, global conformational change involving reorientation of
the four helix bundles in each of its two domains. This conformational change
upon ion binding is a key component of the signal transduction and regulatory
roles of CaM, yet the precise nature of this transition is still unclear. Here,
we present a 1.3-A structure of zinc-bound N-terminal calmodulin (N-CaM) solved
by single-wavelength anomalous diffraction phasing of a selenomethionyl N-CaM.
Our zinc-bound N-CaM structure differs from previously reported CaM structures
and resembles calcium-free apo-calmodulin (apo-CaM), despite the zinc binding to
both EF-hand motifs. Structural comparison with calcium-free apo-CaM,
calcium-loaded CaM, and a cross-linked calcium-loaded CaM suggests that our
zinc-bound N-CaM reveals an intermediate step in the initiation of metal ion
binding at the first EF-hand motif. Our data also suggest that metal ion
coordination by two key residues in the first metal-binding site represents an
initial step in the conformational transition induced by metal binding. This is
followed by reordering of the N-terminal region of the helix exiting from this
first binding loop. This conformational switch should be incorporated into
models of either stepwise conformational transition or flexible, dynamic
energetic state sampling-based transition.
|
|
|
|
|
|
|
|
Figure 3.
Fig. 3. Structure alignment of N-CaM with N-terminal domain
of the NMR structure of apo-CaM (left, 1CFD) and the X-ray
structure of Ca^2+-CaM (right, 1CLL). The residues involved in
ion coordination are shown as sticks and labeled. These global
alignments were performed using helices A and D, and show that
our structure is predominantly in the closed conformation. 1CFD
and 1CLL are presented as transparent. The two
helix–loop–helix EF-hand Zn^2+-binding sites are shown in
different colors: EF-hand I (helices A and B), rose red; EF-hand
II (helices C and D), lime green. The spheres show the two Zn^2+
ions present in these binding sites. The zinc ion in site 2 has
double occupancy. There is also a cacodylate molecule present
from the crystal growth buffer with arsenic shown in purple.
|
|
Figure 4.
Fig. 4. The effect of zinc ion on the activation of two
bacterial adenylyl cyclase toxins, EF and CyaA, by CaM. Assays
were performed at 30 °C for 10 min in the presence of 1 nM
EF or CyaA with the indicated concentration of CaM either with
10 mM ZnCl[2] or 1 μM free calcium ion buffered by EGTA; data
are a representative of two experiments.
|
|
|
|
|
|
The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2007,
374,
517-527)
copyright 2007.
|
|
|
|
|
|
|
