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PDBsum entry 1ytz
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Contractile protein
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PDB id
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1ytz
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Contents |
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90 a.a.
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141 a.a.
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159 a.a.
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References listed in PDB file
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Key reference
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Title
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Ca(2+)-Regulated structural changes in troponin.
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Authors
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M.V.Vinogradova,
D.B.Stone,
G.G.Malanina,
C.Karatzaferi,
R.Cooke,
R.A.Mendelson,
R.J.Fletterick.
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Ref.
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Proc Natl Acad Sci U S A, 2005,
102,
5038-5043.
[DOI no: ]
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PubMed id
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Abstract
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Troponin senses Ca2+ to regulate contraction in striated muscle. Structures of
skeletal muscle troponin composed of TnC (the sensor), TnI (the regulator), and
TnT (the link to the muscle thin filament) have been determined. The structure
of troponin in the Ca(2+)-activated state features a nearly twofold symmetrical
assembly of TnI and TnT subunits penetrated asymmetrically by the
dumbbell-shaped TnC subunit. Ca ions are thought to regulate contraction by
controlling the presentation to and withdrawal of the TnI inhibitory segment
from the thin filament. Here, we show that the rigid central helix of the sensor
binds the inhibitory segment of TnI in the Ca(2+)-activated state. Comparison of
crystal structures of troponin in the Ca(2+)-activated state at 3.0 angstroms
resolution and in the Ca(2+)-free state at 7.0 angstroms resolution shows that
the long framework helices of TnI and TnT, presumed to be a Ca(2+)-independent
structural domain of troponin are unchanged. Loss of Ca ions causes the rigid
central helix of the sensor to collapse and to release the inhibitory segment of
TnI. The inhibitory segment of TnI changes conformation from an extended loop in
the presence of Ca2+ to a short alpha-helix in its absence. We also show that
Anapoe, a detergent molecule, increases the contractile force of muscle fibers
and binds specifically, together with the TnI switch helix, in a hydrophobic
pocket of TnC upon activation by Ca ions.
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Figure 3.
Fig. 3. Superposition of the structures of chicken skeletal
muscle troponin and human cardiac troponin in the
Ca^2+-saturated state. The structure of cardiac troponin (28)
(PDB ID code 1J1D [PDB]
; chains A, B, and C) is shown in gray. Arrows indicate
deviations.
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Figure 5.
Fig. 5. Cartoon representation of the conformational
changes occurring in troponin during muscle contraction. For
color coding, see the legend to Fig. 1. Ca ions are shown as
black circles. The hydrophobic pocket opened in the N-terminal
lobe of TnC is colored in green. The switch segment and the
inhibitory segment of TnI are indicated.
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