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PDBsum entry 1clm
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Calcium-binding protein
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PDB id
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1clm
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References listed in PDB file
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Key reference
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Title
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Structure of paramecium tetraurelia calmodulin at 1.8 a resolution.
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Authors
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S.T.Rao,
S.Wu,
K.A.Satyshur,
K.Y.Ling,
C.Kung,
M.Sundaralingam.
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Ref.
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Protein Sci, 1993,
2,
436-447.
[DOI no: ]
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PubMed id
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Abstract
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The crystal structure of calmodulin (CaM; M(r) 16,700, 148 residues) from the
ciliated protozoan Paramecium tetraurelia (PCaM) has been determined and refined
using 1.8 A resolution area detector data. The crystals are triclinic, space
group P1, a = 29.66, b = 53.79, c = 25.49 A, alpha = 92.84, beta = 97.02, and
gamma = 88.54 degrees with one molecule in the unit cell. Crystals of the
mammalian CaM (MCaM; Babu et al., 1988) and Drosophila CaM (DCaM; Taylor et al.,
1991) also belong to the same space group with very similar cell dimensions. All
three CaMs have 148 residues, but there are 17 sequence changes between PCaM and
MCaM and 16 changes between PCaM and DCaM. The initial difference in the
molecular orientation between the PCaM and MCaM crystals was approximately 7
degrees as determined by the rotation function. The reoriented Paramecium model
was extensively refitted using omit maps and refined using XPLOR. The R-value
for 11,458 reflections with F > 3 sigma is 0.21, and the model consists of
protein atoms for residues 4-147, 4 calcium ions, and 71 solvent molecules. The
root mean square (rms) deviations in the bond lengths and bond angles in the
model from ideal values are 0.016 A and 3 degrees, respectively. The molecular
orientation of the final PCaM model differs from MCaM by only 1.7 degrees. The
overall Paramecium CaM structure is very similar to the other calmodulin
structures with a seven-turn long central helix connecting the two terminal
domains, each containing two Ca-binding EF-hand motifs. The rms deviation in the
backbone N, Ca, C, and O atoms between PCaM and MCaM is 0.52 A and between PCaM
and DCaM is 0.85 A. The long central helix regions differ, where the B-factors
are also high, particularly in PCaM and MCaM. Unlike the MCaM structure, with
one kink at D80 in the middle of the linker region, and the DCaM structure, with
two kinks at K75 and I85, in our PCaM structure there are no kinks in the helix;
the distortion appears to be more gradually distributed over the entire helical
region, which is bent with an apparent radius of curvature of 74.5(2) A. The
different distortions in the central helical region probably arise from its
inherent mobility.
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Figure 1.
Fig. 1. Theprimarysequnce of mammalianCaM (top line)iscompared
withParameciumCaM(middleline)and rosophila CaM (bottomline).
Residuesthatare common withmammalianCaMareindicated by -.
Thehelicaland calcium-binding sites aremarkedandthe loo residues
involved n calcium bindingaremarkedwith *,
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Figure 2.
Fig. 2. Ribbondiagram (Priestle, 1988) of PCaM. The helicalregions
A through H remarked, as ell as thetermini.
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The above figures are
reprinted
from an Open Access publication published by the Protein Society:
Protein Sci
(1993,
2,
436-447)
copyright 1993.
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