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PDBsum entry 1uow
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Crystallographic identification of ca2+ and sr2+ coordination sites in synaptotagmin i c2b domain.
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Authors
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Y.Cheng,
S.M.Sequeira,
L.Malinina,
V.Tereshko,
T.H.Söllner,
D.J.Patel.
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Ref.
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Protein Sci, 2004,
13,
2665-2672.
[DOI no: ]
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PubMed id
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Abstract
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Synaptotagmin I has two tandem Ca(2+)-binding C(2) domains, which are essential
for fast synchronous synaptic transmission in the central nervous system. We
have solved four crystal structures of the C(2)B domain, one of them in the
cation-free form at 1.50 A resolution, two in the Ca(2+)-bound form at 1.04 A
(two bound Ca(2+) ions) and 1.65 A (three bound Ca(2+) ions) resolution and one
in the Sr(2+)-bound form at 1.18 A (one bound Sr(2+) ion) resolution. The side
chains of four highly conserved aspartic acids (D303, D309, D363, and D365) and
two main chain oxygens (M302:O and Y364:O), together with water molecules, are
in direct contact with two bound Ca(2+) ions (sites 1 and 2). At higher Ca(2+)
concentrations, the side chain of N333 rotates and cooperates with D309 to
generate a third Ca(2+) coordination site (site 3). Divalent cation binding
sites 1 and 2 in the C(2)B domain were previously identified from NMR NOE
patterns and titration studies, supplemented by site-directed mutation analysis.
One difference between the crystal and NMR studies involves D371, which is not
involved in coordination with any of the identified Ca(2+) sites in the crystal
structures, while it is coordinated to Ca(2+) in site 2 in the NMR structure. In
the presence of Sr(2+), which is also capable of triggering exocytosis, but with
lower efficiency, only one cation binding site (site 1) was occupied in the
crystallographic structure.
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Figure 1.
Figure 1. Structure of C[2]B-B. (A) Front and side view of
ribbon diagrams of the structure of C[2]B-B with 2 Ca^2+ ions.
 -Strands are
labeled from 1 to 8, while helices are labeled H1 and H2. Ca^2+
ions are labeled Ca1 and Ca2. (B) Front and back view of
electrostatic potential surface of C[2]B-B. The acidic and basic
residues are colored green and orange, respectively.
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Figure 3.
Figure 3. Cation-binding sites in (A) superpositioned
C[2]B-NMR structures and (B) C[2]B-B, (C) C[2]B-C, and (D)
C[2]B-D crystal structures. The Ca^2+ and Sr2+ ions are colored
orange. The oxygen atoms that coordinate the cations are colored
red. Water molecules are represented as small red spheres.
Dashed lines indicate pentagonal bipyramidyl coordination to
Ca^2+ sites (B,C) and tetragonal bipyramidyl coordination to
Sr2+ site (D) in the crystal structures.
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The above figures are
reprinted
by permission from the Protein Society:
Protein Sci
(2004,
13,
2665-2672)
copyright 2004.
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