'''Solution structure of actin-binding domain of troponin in Ca2+-free state'''
===Solution structure of actin-binding domain of troponin in Ca2+-free state===
==Overview==
<!--
Troponin and tropomyosin on actin filaments constitute a Ca2+-sensitive switch that regulates the contraction of vertebrate striated muscle through a series of conformational changes within the actin-based thin filament. Troponin consists of three subunits: an inhibitory subunit (TnI), a Ca2+-binding subunit (TnC), and a tropomyosin-binding subunit (TnT). Ca2+-binding to TnC is believed to weaken interactions between troponin and actin, and triggers a large conformational change of the troponin complex. However, the atomic details of the actin-binding sites of troponin have not been determined. Ternary troponin complexes have been reconstituted from recombinant chicken skeletal TnI, TnC, and TnT2 (the C-terminal region of TnT), among which only TnI was uniformly labelled with 15N and/or 13C. By applying NMR spectroscopy, the solution structures of a "mobile" actin-binding domain (approximately 6.1 kDa) in the troponin ternary complex (approximately 52 kDa) were determined. The mobile domain appears to tumble independently of the core domain of troponin. Ca2+-induced changes in the chemical shift and line shape suggested that its tumbling was more restricted at high Ca2+ concentrations. The atomic details of interactions between actin and the mobile domain of troponin were defined by docking the mobile domain into the cryo-electron microscopy (cryo-EM) density map of thin filament at low [Ca2+]. This allowed the determination of the 3D position of residue 133 of TnI, which has been an important landmark to incorporate the available information. This enabled unique docking of the entire globular head region of troponin into the thin filament cryo-EM map at a low Ca2+ concentration. The resultant atomic model suggests that troponin interacted electrostatically with actin and caused the shift of tropomyosin to achieve muscle relaxation. An important feature is that the coiled-coil region of troponin pushed tropomyosin at a low Ca2+ concentration. Moreover, the relationship between myosin and the mobile domain on actin filaments suggests that the latter works as a fail-safe latch.
The line below this paragraph, {{ABSTRACT_PUBMED_16061251}}, adds the Publication Abstract to the page
(as it appears on PubMed at http://www.pubmed.gov), where 16061251 is the PubMed ID number.
-->
{{ABSTRACT_PUBMED_16061251}}
==About this Structure==
==About this Structure==
1VDI is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Gallus_gallus Gallus gallus]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1VDI OCA].
1VDI is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Gallus_gallus Gallus gallus]. Full experimental information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1VDI OCA].
==Reference==
==Reference==
Line 31:
Line 35:
[[Category: Tropomyosin]]
[[Category: Tropomyosin]]
[[Category: Troponin]]
[[Category: Troponin]]
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 12:24:39 2008''
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 23:00:38 2008''
Revision as of 23:00, 28 July 2008
This article has been automatically seeded. Changes to this page should pertain to the PDB entry only and not to the protein or biomolecule in general.
