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PDBsum entry 2hf5
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Metal binding protein
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PDB id
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2hf5
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References listed in PDB file
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Key reference
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Title
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Calcium-Induced folding of a fragment of calmodulin composed of ef-Hands 2 and 3.
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Authors
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T.M.Lakowski,
G.M.Lee,
M.Okon,
R.E.Reid,
L.P.Mcintosh.
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Ref.
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Protein Sci, 2007,
16,
1119-1132.
[DOI no: ]
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PubMed id
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Abstract
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Calmodulin (CaM) is an EF-hand protein composed of two calcium (Ca(2+))-binding
EF-hand motifs in its N-domain (EF-1 and EF-2) and two in its C-domain (EF-3 and
EF-4). In this study, we examined the structure, dynamics, and Ca(2+)-binding
properties of a fragment of CaM containing only EF-2 and EF-3 and the
intervening linker sequence (CaM2/3). Based on NMR spectroscopic analyses,
Ca(2+)-free CaM2/3 is predominantly unfolded, but upon binding Ca(2+), adopts a
monomeric structure composed of two EF-hand motifs bridged by a short
antiparallel beta-sheet. Despite having an "even-odd" pairing of
EF-hands, the tertiary structure of CaM2/3 is similar to both the
"odd-even" paired N- and C-domains of Ca(2+)-ligated CaM, with the
conformationally flexible linker sequence adopting the role of an inter-EF-hand
loop. However, unlike either CaM domain, CaM2/3 exhibits stepwise Ca(2+) binding
with a K (d1) = 30 +/- 5 microM to EF-3, and a K (d2) > 1000 microM to EF-2.
Binding of the first equivalent of Ca(2+) induces the cooperative folding of
CaM2/3. In the case of native CaM, stacking interactions between four conserved
aromatic residues help to hold the first and fourth helices of each EF-hand
domain together, while the loop between EF-hands covalently tethers the second
and third helices. In contrast, these aromatic residues lie along the second and
third helices of CaM2/3, and thus are positioned adjacent to the loop between
its "even-odd" paired EF-hands. This nonnative hydrophobic core
packing may contribute to the weak Ca(2+) affinity exhibited by EF-2 in the
context of CaM2/3.
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Figure 5.
Figure 5. CaM2/3 superimposed onto the domains of CaM. (A,B) The
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Figure 6.
Figure 6. Backbone
15
N relaxation data for Ca
2+
-saturated CaM2/3. (A) The longitudinal (T1) and (B) transverse (T2)
15
N relaxation
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The above figures are
reprinted
by permission from the Protein Society:
Protein Sci
(2007,
16,
1119-1132)
copyright 2007.
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